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Assignment 2A For students with first names starting with the letters A to G. This assignm, Exams of Nursing

Utah Valley University (UVU)Nursing

Prof. Weslie E. Sheldon

Cell Division Eukaryotes Mitosis serves to divide the replicated DNA equally and precisely Meiosis produces daughter nuclei where they have only half the chromosome as the parental nuclei, and may be in different combination – may function as gametes/spores Cell cycle – period of growth, nuclear division and cytokinesis Chromosomes – nuclear units of genetic information that are divided and distributed by mitotic cell division Diploid 2n – two copies of each type of chromosome in nuclei – most eukaryotes

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BIOL 204 Exam Notes - Final.

•

• Cell Division

• Eukaryotes

• Mitosis serves to divide the replicated DNA equally and precisely

• Meiosis produces daughter nuclei where they have only half the

chromosome as the parental nuclei, and may be in different

combination – may function as gametes/spores

• Cell cycle – period of growth, nuclear division and cytokinesis

• Chromosomes – nuclear units of genetic information that are divided and

distributed by mitotic cell division

• Diploid 2n – two copies of each type of chromosome in nuclei

– most eukaryotes

• Haploid n – one copy of each type of chromosome –

microorganisms

• Ploidy - # of chromosome sets

• Replication of DNA of each chromosome creates 2 sister chromatids,

held together until separated by mitosis

• Mitosis

• Interphase – 1st and longest phase, begins when daughter cell

from previous cycle enters cytoplasmic growth – cell grows and

replicates DNA in preparation for mitosis and cytokinesis

• G1 phase – cell replications of cellular molecules

excluding nuclear DNA

• If stop dividing – G0 phase

• When cell is going to divide, DNA replication begins,

initiating S phase – DNA synthesis, duplicate

chromosomal proteins and DNA

• G2 phase – cell continues to synthesize RNAs and

proteins and grow – end of G2 marks end of interphase,

mitosis begins

• Prophase – chromosomes condense, nucleolus disappears,

shutting down all types of RNA synthesis

• Mitotic spindle form between centrosomes as they

move towards spindle poles

• In the end, nuclear envelop breaks down

• Prometaphase – spindle microtubules grown from centrosomes at

opposing spindle poles toward the centre of cell

• Two sister chromatids held together by centromeres,

kinetochore formed on each chromatid at centromere and

bind to the microtubules – determine the outcome of

mitosis

• Microtubules not attached overlap those at opposite end

Partial preview of the text

Download Assignment 2A For students with first names starting with the letters A to G. This assignm and more Exams Nursing in PDF only on Docsity!

BIOL 204 Exam Notes - Final.

Cell Division
- Eukaryotes
  - Mitosis serves to divide the replicated DNA equally and precisely
  - Meiosis produces daughter nuclei where they have only half the chromosome as the parental nuclei, and may be in different combination – may function as gametes/spores
  - Cell cycle – period of growth, nuclear division and cytokinesis
  - Chromosomes – nuclear units of genetic information that are divided and distributed by mitotic cell division - Diploid 2n – two copies of each type of chromosome in nuclei - most eukaryotes - Haploid n – one copy of each type of chromosome – microorganisms - Ploidy - # of chromosome sets
  - Replication of DNA of each chromosome creates 2 sister chromatids, held together until separated by mitosis
  - Mitosis
    - Interphase – 1st^ and longest phase, begins when daughter cell from previous cycle enters cytoplasmic growth – cell grows and replicates DNA in preparation for mitosis and cytokinesis - G 1 phase – cell replications of cellular molecules excluding nuclear DNA - If stop dividing – G 0 phase - When cell is going to divide, DNA replication begins, initiating S phase – DNA synthesis, duplicate chromosomal proteins and DNA - G 2 phase – cell continues to synthesize RNAs and proteins and grow – end of G 2 marks end of interphase, mitosis begins
    - Prophase – chromosomes condense, nucleolus disappears, shutting down all types of RNA synthesis - Mitotic spindle form between centrosomes as they move towards spindle poles - In the end, nuclear envelop breaks down
    - Prometaphase – spindle microtubules grown from centrosomes at opposing spindle poles toward the centre of cell - Two sister chromatids held together by centromeres, kinetochore formed on each chromatid at centromere and bind to the microtubules – determine the outcome of mitosis - Microtubules not attached overlap those at opposite end

Metaphase – spindle reaches its final form, moves chromosomes into alignment at metaphase plate - Chromosomes complete condensation in this stage, assume the shape determined by the location of centromere and length/thickness of chromatid arms - The complete collection of chromosomes arranged according to size and shape forms karyotype of species
Anaphase – sister chromatids separate and move to opposite spindle poles - Movement continues until chromatids/daughter chromosomes reached two poles – chromosome segregation completed
Telophase – spindle dissembles, chromosomes decondense, nucleolus reappears, RNA transcription resumes, new nuclear envelope forms around chromosomes at each pole, producing two daughter nuclei - Nuclear division complete
Cytokinesis – division of cytoplasm, begins during telophase or late anaphase - Animals – furrow, girdles the cell and gradually deepens until cytoplasm cut in two - Plants – cell plate forms between daughter nuclei
Cell cycle regulation – Cell cycle has built-in checkpoints
Cyclin-dependent kinase – CDK – enzymes adding phosphate groups to target protein, switched on when combined with cyclin protein
Different cyclin – CDK combinations regulate cell cycle transitions at different checkpoints
Indirect control by alter the activity of cyclin:CDK complex at each key checkpoint – blocking until one phase is complete before the next starts
External controls – modify internal controls speed/slow/stop cell division by inhibiting/stimulating cyclin:CDK
Cell-surface receptors recognize contact with other cells or molecules, trigger internal reaction pathways, inhibit division by arresting cell cycle – contact inhibition
Stabilize cell growth when no longer needed
Shunt from G 1 to G 0
Cellular senescence – loss of dividing ability of cell – may be caused by DNA damage or telomere shortening
Prokaryotes – binary fission – splitting/dividing into two pairs
Single circular DNA – bacterial chromosome, DNA replication take place majority of the time between cytoplasmic division – once replication complete, cytoplasm divide to complete cell cycle
Origin of replication (ori) – where enzymes of DNA replication

As DNA polymerases can add nucleotides only to the 3’ end of existing strand, to begin a new strand, primer was used - Primer, made of RNA assembled by primase, laid down as the first series of nucleotides in new DNA strand – later removed and replaced by DNA
Direction is 5’3’, antiparallel to template strand
DNA polymerase assemble new DNA strand on a template strand in 5’ to 3’ direction, only one of the template strands runs in a direction that allows DNA polymerase to make a 5’ to 3’ complimentary copy in the direction of unwinding
New DNA strand is synthesized continuously in the direction of unwinding of double helix, the other template strand runs in opposite direction – DNA polymerase has to copy in the opposite direction of unwinding
Polymerases make this strand in short lengths/Okazaki fragments synthesized in the direction opposite to that of DNA unwinding – discontinuous replication covalently linked to continuous polynucleotide chain
Leading strand – new strand assembled in direction of unwinding, 5’3’
Lagging strand – strand assembled discontinuously in the opposite direction – 3’5’
Nucleotides enter to newly synthesized chain according to A-T, G-C
Helicase, primase and DNA polymerase coordinate activities with additional enzymes to replicate DNA
Helicase unwinds template DNA to produce a replication fork
Primase lay down short RNA primers behind the site of unwinding, which primers assembled in 5’3’ direction on both template chains – in & opposite direction
DNA polymerase adds DNA nucleotides to RNA primers
Helicase continues to unwind DNA, leading strand synthesis continues in direction of unwinding; primase creating new RNA primer on lagging strand, where DNA polymerase adds DNA nucleotides to the new primer
When second fragment reaches the primer of the first fragment, DNA polymerase leaves and a different types of DNA polymerase binds, removing RNA primer on the first fragment and replace with DNA nucleotide
Two newly synthesized fragments are not covalently joined – nick in between
DNA ligase close the nick, joining two fragments
Replication enzymes operate only at the replication fork, new

DNA chains are fully continuous and wound with their template strands into complete DNA double helices behind the fork – each consists of one old, one new

Telomerases solve specialized replication problem
- Telomeres – nonprotein coded sequences located at the ends of each eukaryotic chromosome as protective buffer of genes - Gap is produced at the 5’ end of new strand made starting at the other end of the chromosome – new chromosome will be shorter
- With each replication, a fraction of the telomere repeats is lost, but the genes are unaffected – buffering fails only when the entire telomere is lost, cell dies after fixed amount of mitotic divisions
- Telomerase can maintain the buffer by adding telomere repeats to the chromosome ends - Telomerase – present in all eukaryotes – adds telomere repeats to the end of template strand before DNA replication begins - Primer of leading strand is laid down using the telomeres as templates - DNA polymerase then extend new DNA strand as usual, primer is removed, leaves unfilled gap at the beginning of leading chain – far from coding regions
Replication begins at replication origins, recognized by proteins bind to the DNA and stimulate helicases to start the unwinding, followed by primer synthesis and DNA replication
Generally, replication proceeds from both sides of a replication origin, producing two replication forks that move in opposite directions – forks eventually meet along the chromosomes to produce fully replicated DNA molecules
Replication origin activated only once during S phase of eukaryotic cell cycle, no portion of DNA is replicated more than once
Replication mistake correction
Base-pair mismatches are corrected by proofreading mechanism during replication or by DNA repair mechanism after replication
Proofreading mechanism – depends on the ability of DNA polymerases to back up and remove mispaired nucleotides from DNA strand – only when the most recently added base is correctly paired with its complementary base template strand can the DNA polymerases continue to add nucleotides to growing chain
If mismatched, DNA polymerase reverse with built-in

All proteins associated with DNA that are not histones
Affect gene accessibility by modifying histones to change how the histones associate with DNA in chromatin, by loosening or tightening the association
Others include regulatory proteins – activate or repress the expression of gene; and components of enzyme – protein complexes needed for expression of any gene
Chromatin – complex of DNA and associated proteins, structural building block of chromosome
Prokaryotes – DNA more simply organized with fewer associated proteins, but still associate with 2 classes of proteins – one organizes DNA structurally, one regulates gene activity
Primary DNA molecule of most prokaryotic cells is circular, only one copy per cell – bacterial chromosome
Replication begins from a single origin in DNA circle, forming two forks that travel around the circle in both directions, meet at the opposite side from the origin to complete replication
DNA circle is packed into nucleoid, suspended directly in the cytoplasm with no membrane
Many prokaryotes also contain other DNA molecules – plasmids – in addition to main chromosome of nucleoid
Plasmids have replication origins, duplicated and distributed to daughter cells together with bacterial chromosome during division – replicate independently
In conjugation, DNA replicated by “rolling circle” replication – one strand of plasmid cut and travels into recipient as a linear molecule with other strand remains circular in donor, DNA replicationrestores both strands to double-strandedness, linear molecule recircularize - Leading and lagging strand synthesis occur in separate cells rather than at one replication fork
There are proteins combine with bacterial DNA, some help organize DNA into loops, others are genetic regulatory proteins with similar functions in those of nonhistones of eukaryotes
Prokaryotes – DNA is circular, topoisomerases remove the overtwisting as it forms during replication
Genes to protein – pathway from gene to polypeptide – transcription & translation
Similar in prokaryotes & eukaryotes
Key difference – prokaryotes can transcribe and translate simultaneously, eukaryotes transcribe and process mRNA in nucleus before exporting it to the cytoplasm for translation
One gene-one polypeptide hypothesis – direct relationship of genes & enzymes
Many proteins are not enzymes, many consist of more than one subunit

polypeptide
One gene is needed to encode one protein/polypeptide
RNA – A-U, G-C – 4 RNA bases – adenine, uracil, guanine, cytosine
Genetic code – nucleotide information that specifies amino acid sequence of a polypeptide, at least 3 bases in mRNA have to be used to provide the capacity to code 20 amino acids
Codon – 3-letter genetic code, each three-letter word – triplet
3-letter codon in DNA are first transcribed into complementary 3-letter RNA codons, always reading in 3’ to 5’
mRNAs can bind to ribosomes and cause a transfer RNA, with linked amino acid, to bind to ribosome – each single-codon mRNA would link to the tRNA carrying the amino acid corresponding to the codon
The first codon translated in any mRNA – start/initiator codon
Three codons that don’t specify amino acids – stop codons, or nonsense/termination codons
When a ribosome reaches stop codon, polypeptide synthesis stops and new polypeptide chain released from ribosome
Only 2 amino acids – methionine and tryptophan, are specified by a single codon, rest is represented by 2-
Degeneracy/redundancy
Commaless – words of nucleic acid code are sequential with no indicators to mark the end of one codon ad the beginning of the next – can be read correctly only by starting at the right place – the start codon – there is only one correct reading frame for each mRNA
Universal – with few exceptions, same codons specify same amino acids in all living organisms and viruses
Transcription – information encoded in DNA made into complementary RNA copy, information in one nucleic acid type is transferred to another nucleic acid type
Enzyme RNA polymerase creates RNA sequence that is complementary to the DNA sequence of a given gene
DNA strand is the template strand read by RNA polymerase, RNA transcribed from gene encode a polypeptide – messenger RNA
In general
In a given gene, only one DNA strand acts as template
Only the sequence encoding a single gene serves as template
RNA polymerases catalyze assembly of nucleotides into RNA
Work like DNA polymerases but require no primer
Transcription begins as RNA polymerase binds to DNA and unwinds it near the beginning of gene, 5’3’ using 3’5’ DNA strand as template
RNA polymerases released when finished
Prokaryotes – same RNA polymerase can transcribe all
Eukaryotes – different polyperases for transcribing

small ribonucleoprotein particles – removes introns from pre- mRNA and joins exons together

Ribozyme – RNA molecule that catalyzes a reaction like a protein enzyme
Not a single base of intron is retained in the finished mRNA, nor is a single base removed from exons
Introns contribute to protein variability – introns increase the coding capacity of existing genes through alternative splicing and in generate new proteins by exon shuffling
Alternative splicing – removal of introns from gene is not absolute, in certain locations/conditions, exons may be joined indifferent combinations to produce different mRNAs from a single DNA gene sequence
Greatly increases the number and variety of proteins encoded in the cell nucleus without increasing the size of genome – proteins direct an organism’s functions
Exo shuffling – intron-exon junctions often fall at points dividing major functional regions in encoded proteins, which may allow new proteins to evolve by exon shuffling where existing protein regions/domains already selected for functions are mixed into novel combinations to create new protein
Translation – use of information encoded in RNA to assemble amino acids into polypeptide, information in nucleic acid, in form of nucleotides, is converted into amino acids
mRNA associates with a ribosome, where amino acids linked into polypeptide chains
Ribosomes – ribonucleoprotein particles that carry out protein synthesis by translating mRNA into chains of amino acids
As ribosome moves along mRNA, amino acids specified by mRNA are joined to form polypeptide chain
Similar in structure and function in prokaryotes and eukaryotes
Different molecular structure give distinct properties
Has special binding sites active in bringing together mRNA with aminoacyl-tRNAs
A site – aminoacyl site – incoming aminoacyl-tRNA , carrying next amino acid to be added to the polypeptide chain, binds to mRNA
P site – peptidyl site – tRNA carrying the growing polypeptide chain is bound
E site – exit site – where existing tRNA binds as it leaves ribosome
Prokaryotes – translation takes place throughout the cell, similar process with eukaryotes
mRNA produced in transcription not confined in nucleus,

therefore available immediately for translation

Ribosomes carry assembly functions throughout cell
Stages in translation
- Initiation – assembly of all translation components on the start codon of mRNA - rRNA of ribosomal subunit finds region with start codon directly by base pairing with a specific ribosome binding site on the mRNA - Large ribosomal subunit then binds to the small one to complete the ribosome - After the initiator tRNA pairs with AUG initiator codon, subsequent stages of translation simply read the nucleotide bases three at a time on mRNA, establish the correct reading frame
- Elongation – reading the string of codons in mRNA while assembling the specified amino acids into a polypeptide – faster than eukaryotes
- Termination – completes the translation process when last amino acid has been added to the polypeptide
Eukaryotes – translation occur mostly in cytoplasm, with few exceptions take place in mitochondria and chloroplast
mRNA produced by splicing of pre-mRNA first exists the nucleus before translated in cytoplasm
mRNA associates with a ribosome and tRNAs brings amino acids to the complex to be joined into polypeptide chain, which sequence is determined by the sequence of codons in mRNA
tRNAs can base pair with themselves to wind into four double- helical segments
At one tip – anticodon, the three-nucleotide segment that pairs with a codon in mRNAs
At the other end, a double-helical segment that links to the amino acid corresponding to the anticodon
Wobble hypothesis – complete set of codons can be read by fewer tRNAs because of the particular pairing properties of bases in anticodons
Pairing of anticodon of first two nucleotides of codon is always precise, with more flexibility in pairing with the third nucleotide of the codon
Same tRNA’s anticodon can read codons with either U/C, A/G
Aminoacylation/charging – adding amino acid to tRNA
tRNA linked to correct amino acid – aminoacl-tRNA
aminoacyl-tRNA synthetases – enzymes catalyzing aminoacylation
Energy eventually drives formation of the peptide bond

tRNA in P site and form a peptide bond with amino acid on tRNA in A,catalyzed by peptidyl transferase in rRNA

Polypeptide chain attached to tRNA in A site, empty tRNA remains at P site
1. Ribosome moves/translocates along mRNA to the next codon, GTP as energy
Two tRNAs remains bound to respective codons, position peptidyl-tRNA in P and generates a vacant A; empty tRNA in P moves to E
With A empty and peptidyl-tRNA in P, ribosome repeats elongation cycle
With turns of cycle, growing polypeptide on tRNA in P is transferred to the amino acid on A tRNA, growing polypeptide chain extends from ribosome through exit tunnel as elongation continues
Termination – completes the translation process when last amino acid has been added to the polypeptide
1. Elongation switched to termination when A of a ribosome arrives at one of the stop codons – UAA/UAG/UGA – on the mRNA
1. When a stop codon appears at A, a protein release factor/termination factor binds to A instead of aminoacyl-tRNA
1. Polypeptide chain is released from tRNA at P site as usual
1. With no amino acid present in A, freed polypeptide chain is released from ribosome while ribosomal subunits separate and detach from the mRNA, empty tRNA and release factor are also released
Same in prokaryotes and eukaryotes
Once first ribosome has begun translating, another one can assemble with an initiator tRNA as soon as there is room on mRNA
Ribosomes continue to attach as translation continues and becomes spaced along the mRNA – polysome
Multiple ribosomes greatly increase the overall rate of polypeptide synthesis from a single mRNA
Eukaryotes – most proteins are in inactive unfinished form with released from ribosomes, which then fold into final shapes as processing reaction take place
Chaperones/chaperonins assist the folding process by combining with folding protein, promoting correct structure and inhibit incorrect ones

At times, same initial polypeptide may be processed by alternative pathway that produce different mature polypeptides by removing different amino acids from interior of polypeptide chain - Alternative processing increase number the proteins encoded by a single gene
Other proteins are later activated by removing a covering segment of the amino acid chain – prevent from degraded by enzyme
Proteins remained in cytoplasmic solution have no signals – made of free ribosomes, suspended in cytosol
Other proteins have sorting signals formed with amino acid sequences, directing them to their cellular locations or out
Signals coded in DNA, transcribed into mRNA, printed in proteins as they are made; recognized and bound by receptors in locations where the proteins are addressed
Signal peptide/signal sequence – first part of polypeptide chain – when emerge from ribosome, signal recognition particle SRP binds to it and temporarily blocks further translation - Then binds with SRP receptor on ER membrane, protein pushed into ER for synthesis
Nuclear proteins include a signal bound by receptors in pore complexes of nuclear envelope, retain signals as they need to move in and out
Prokaryotes – signals similar to eukaryotes, direct proteins in or out of plasma membrane – those with no signals remain in cytoplasm
Absence of nuclear envelope allows transcription and translation to be tightly coupled, regulate production of proteins very quickly in response to changing environmental conditions
Base-pair mutations can affect protein structure and function
Mutations – changes in the sequence of bases in the genetic material
Base-pair substitution mutations – change of one particular base to another in genetic material, changing base in a codon
Missense mutation – wrong amino acid in protein
Whether polypeptide’s function is altered depends on which amino acid is changed and what it is changed to
Nonsense mutation – mutation changes a sense – amino acid-coding – codon to a nonsense – termination – codon in the mRNA
Premature termination with abnormally short polypeptide that’s partially functional at best
Silent mutation – did not alter the amino acid specified by the gene as the changed codon specifies the same amino acid as in the normal polypeptide
Frameshift mutation – if single base pair is deleted or inserted in the coding region of a gene, resulting mRNA is altered
Ribosome reads different codons than for the normal mRNA, producing completely different amino acid sequence that’s

functional differences in protein or RNA product encoded by the gene

detected as distinct phenotypes in offspring of a cross
New findings
Incomplete dominance – effects of recessive alleles can be detected in heterozygotes – 1:2:
Dominance of alleles is complete or incomplete often depends on level which the effects of alleles are examined
Codominance – two alleles have approximately equal effects
Multiple alleles – more than two different alleles of a gene, may present if all individuals of a population are taken into account
Although any one individual have only two alleles of the gene, there are more than two alleles in the population as a whole
Multiple alleles of a gene each contain differences at one or more points in their DNA sequences, causing detectable alteration sin structure and function of gene products
Eg human ABO blood group
A have antigen A, B have antigen B, AB have both, O have neither
Antibodies – AB, BA, OA&B, AB have none
Epistasis – genes interact with 1+ alleles of a gene at one locus inhibiting/masking the effects of 1+ alleles of a gene at different locus
Some expected phenotypes do not appear among offspring
Polygenic inheritance – several to many different genes contribute to the same character – quantitative traits
Often modified by environment, detectable by defining classes of a variation – plot into a graph, quantitative if bell-shaped
Pleiotropy – single genes affect more than one character
Control of gene expression
Prokaryotic regulation of gene expression
Typically rapid and reversible alterations in biochemical pathways allow them to adapt quickly to changes in their environment
Operon – a cluster of prokaryotic genes and DNA sequences involved in gene regulation
Promoter – a region where RNA polymerase begins transcription
Each operon contains several genes and is transcribed as a unit form the promoter into mRNA – transcription unit
Ribosome translates mRNA from one end to the other, making each protein encoded in the mRNA
Operator – short segment where regulatory protein binds
Repressor – when active, prevents the genes of operon from being expressed
Activator – when active, stimulates the expression of genes
Negative regulatory system

Inducible Operons – Eg lac operon for lactose metabolism is transcribed when inducer inactivates a repressor - Lac operon was controlled by lac repressor, which is synthesized in active form - Lac repressor binds to the operator, blocks RNA polymerase from binding to the promoter – transcription can’t occur - When lactose added, lac operon is turned on , all enzymes are synthesized rapidly - Some lactose is converted to allolactose when entered – inducer for lac operon, turns all enzymes on by binding to the lac repressor and alter its shape to inactivate it - Repressor no longer binds to the operator - RNA polymerase then able to bind to the promoter to transcribe genes - Lac operon therefore an inducible operon – operon whose expression increased by inducer
Repressible Operons – Eg trp operon gene transcription repressed when tryptophan activates a repressor - Trp repressor synthesized in an inactive form where it cannot bind to the operator - For trp operon, presence of tryptophan represses the expression of tryptophan biosynthesis genes – repressible operon - Tryptophan acts as corepressor – regulatory molecule that combines with a repressor to activate it, shutting off the operon
Lac vs trp
- Lac – repressor synthesized in active form
  - When inducer is present, it binds to the prepressor and inactivates it – operon transcribed
- Trp – repressor synthesized in inactive form
  - When corepressor is present, it binds to the repressor and activates it – block transcription of operon
Positive regulatory system – Eg lac operon
Lacoperon transcribed if lactose is provided as energy source, but not if glucose is also present
Lactose is metabolized to the inducer that binds and inactivates lac repressor, RNA polymerase then recruited to the promoter by active CAP at the CAP site – activator, stimulates gene expression, synthesized in inactive form and is activated when cAMP binds to it
cAMP is abundant in the absence of glucose – active CAP
If lactose and glucose are present, lac operon is not transcribed

DNA to loop around itself

Interactions between coactivator, proteins at promoter, and RNA polymerase stimulate transcription to maximal rate
Repressors oppose the effect of activators and block/reduce the rate of transcription
Some bind to same regulatory sequence as activator, preventing activators from binding
Some bind to their own specific site in DNA where repressor interact with the activator so that it cannot interact with coactivator
Some recruit histone decetylation enzymes that modify histones – chromatin compaction and making a gene’s promoter inaccessible to the transcription machinery
Combinatorial gene regulation – combine few regulatory proteins in a particular ways, transcription of array of genes can be controlled, large number of cell types can be specified
Characteristics of genes is the number/types of promoter proximal elements
All genes that are coordinately regulated have the same associated regulatory sequences
Transcription of all genes can be controlled simultaneously
All genes regulated by a specific steroid hormone have same DNA sequence to which the hormone receptor complex binds – steroid hormone response element
Hormone – produced by one tissue and transported via bloodstream to another specific tissue to alter its physiological activity
Steroid – type of lipid derived from cholesterol
DNA methylation – a methyl group is added enzymatically to C base of DNA, inhibits transcription
silencing
May silence large blocks of genes or chromosomes
Include chromotain modification
Genomic imprinting – methylation permanently silences transcription of either the inherited maternal/paternal allel of a gene
Occurs during gametogenesis in a parent – inherited methylated allele is silenced – imprinted allele – expression of gene depends on expression of nonimprinted allele inherited from the other parent

Methylation of parental allele is maintained as DNA is replicated – remains inactive in progeny cells
Posttranscriptional regulation – pre-mRNA processing and movement of finished mRNAs to cytoplasm
Pre-mRNAs processing can regulate which proteins are made in cells
Alternative splicing produces different mRNAs by removing different combinations of exons along with introns – noncoding spacers; resulting mRNAs translated to produce a family of related proteins with various combinations of amino acid sequences derived from exons
Masking proteins bind to mRNAs, make them unavailable for protein synthesis
Rate of mRNAs breakdown can be directly/indirectly controlled by regulatory molecule
RNA interference RNAi – caused by micro- RNA or small interfering RNA siRNA binding to mRNA with complementary sequence, silencing genes
Protein in complex cleave mRNA where miRNA is bound
Double-stranded segment formed between miRNA and mRNA blocks ribosomes from translating mRNA
Targets of miRNA are often mRNAs regulating the development of the organism
Translational regulation – controls rate of protein synthesis
Adjusting length of poly(A) tail of mRNA by enzymes
Shortening – decrease translation
Lengthening – increase translation
Posttranslational regulation – controls availability of functional proteins – 3 ways
Viruses
Chemical modification – add/remove chemical groups, reversibly alters

Assignment 2A For students with first names starting with the letters A to G. This assignm, Exams of Nursing

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Download Assignment 2A For students with first names starting with the letters A to G. This assignm and more Exams Nursing in PDF only on Docsity!

BIOL 204 Exam Notes - Final.