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DNA-RNA-PROTEIN
1) Basics of Transcription and Translation
Generally: DNA →Transcription → RNA → Translation → Protein RNA ➢ Only one polynucleotide strand ➢ Only ribose sugar in RNA ➢ Adenine, Guanine, Cytosine, Uracil ➢ mRNA: messenger RNA carries a copy of a gene sequence in DNA to the site of protein synthesis at the ribosome ➢ tRNA: transfer RNA Carries amino acids to the ribosome for the assembly into polypeptides ➢ rRNA: ribosomal RNA catalyzes peptide bond formation and provides a structural framework for the ribosome ➢ Proteins are synthesized in the cytoplasm ➢ Promoter is a special sequence of DNA to which the RNA polymerase binds tightly ➢ Elongation is a process that unwinds the DNA and allows RNA to collect its nutrients ➢ Polyribosome is a group of ribosomes that create polypeptides ➢ After translation proteins are carried through the cytoplasm into a specific place of work, or they get out of the cell ➢ Proteolysis is a process when the polypeptide chain is broken down into important pieces
➢ Glycosylation means the addition of sugars into the polypeptide chain to construct Glycoproteins
2) What is a Mutation?
Mutations are inherited changes in genes Somatic mutations are those that occur in somatic (body) cells. These mutations are passed on to the daughter cells during mitosis, and to the offspring of those cells in turn, but are not passed on to sexually produced offspring (Individual that can be harmed) Germ line mutations are those that occur in the cells of the germ line — the specialized cells that give rise to gametes. A gamete with the mutation passes it on to a new organism at fertilization (Generation that can be harmed)
3) What kind of different Mutations are there?
A point mutation results from the gain, loss, or substitution of a single nucleotide. After DNA replication, the altered nucleotide becomes a mutant base pair. If a point mutation occurs within a gene then one allele of that gene (usually dominant) becomes another allele (usually recessive) (involves one gene) Chromosomal mutations are more extensive than point mutations. They may change the position or orientation of a DNA segment without actually removing any genetic information, or they may cause a segment of DNA to be duplicated or irretrievably lost (involves more genes) In either case, the mutations may or may not have phenotypic effects
Nonsense Mutations ● Involves a base substitution that causes a stop codon (for translation) to form somewhere in the mRNA ● Results in a shortened protein, since translation does not proceed beyond ● Shortened proteins are usually not functional Frame-Shift Mutations ● Single or double bases may be inserted into or deleted from DNA ● Interfere with the translation of the genetic message by throwing it out of register ● Shift the “reading frame” of the message ● Almost always lead to the production of nonfunctional proteins Loss of Function Mutations ● Codes for nonfunctional proteins that no longer work as structural proteins or enzymes ● Gain of function mutation leads to a protein with an altered function
Conditional Mutations ● Mutations in regards to conditions faced(temperature rises, then the phenotype would change under certain conditions) ● Not detectable under other permissive conditions ● Chromosome mutations happen when a chromosome has a mutation (non- disjunction), it does not mean that the genes have been mutated as well ● Deletions result from the removal of part of the genetic material ● Duplications are the breaking down of homologous chromosomes at different positions and rejoining them with the wrong partners ● Inversions break down the same chromosome and reinsert it into the same location in the chromosome, but in reversed order ● Translocations happen when non-homologous chromosomes break and join other chromosomes (Down syndrome)
5) What triggers Mutations?
● Errors in DNA replication that are not corrected during proofreading ● Environmental mutagens which cause mutations such as radiation / certain chemicals ● Spontaneous mutations are permanent changes in the genetic material that occur without any outside influence: ● Different structures of the 4 nucleotide bases ● DEAMINATION changes bases in DNA ● Errors in replication ● Meiosis is not perfect
Multicellular Cells ➔ Tissue for repair and growth ➔ Eukaryotic cells ➔ DNA replication and division ➔ Many chromosomes ➔ Mitoses or meiosis ➔ Environmental conditions that can influence the cell divisions ➔ Asexual & sexual reproduction ➔ Cytoskeleton moves with DNA along, either actively or passively (rail-road- track) ➔ One chromosome, 99 % formed in a circle
Four main events in cell division:
→ Reproductive signal in or outside cell starts the process → Two cells are formed from one, DNA starts to replicate so that the two new cells will have identical genes and cell functions → Segregation: Cell is distributing the replicated DNA to the two cells → New stuff is added to cells by Cytokinesis ● Cytoskinesis: division of the cytoplasm of a dividing cell ● Two regions of the prokaryotic chromosome play functional roles in cell reproduction: → Ori = the site where replication of the circular chromosome starts (the origin of replication)
→ Ter = the site where replication ends (the terminus of replication ● Cyclins: proteins that help initiate mitosis ● Cyclins: dependent kinase: protein that depends on process above
2) What are Mitosis and Meiosis?
● Mitosis → Division of nucleus forming two daughter nuclei with each identical chromosomes to the original nucleus → Chromatins become more condensed into compact structures → A sexual → offspring are clones
- Meiosis → Sexual reproduction which leads to genetic diversity → Division of nucleus through two nuclear divisions so that four haploid daughter are created Mitosis Meiosis 1 Meiosis 2 Parent cell 2n 2n 2 X 2n Prophase No pairing of homologous chromosomes, kinetochores Pairing of homologous chromosomes(syna psis) Chromosomes condense again
4) How does the cell cycle work?
➔ Cell cycle = period between cell division, two phases mitosis and interphase ➔ A protein called RB, or retinoblastoma protein, is the key to progressing past the restriction point ● Eukaryotic cell division → Mitosis or meiosis followed by cytokinesis → Signal = Cells do not constantly divide but only when needed (Signals are related to the needs of entire organism) → Replication = chromosomes are replicated → Segregation = replicated chromosomes are closely associated to each other (sister chromatids) → mitosis segregates them → Cytokinesis Interphase ➔ Cell nucleus is visible and cell function take place including DNA replication: ➔ G1 - Period between the end of cytokinesis and the onset of S phase
- A cell is preparing for S phase, so at this stage each chromosome is a single, un-replicated structure
- In many cases these cells enter a resting phase called G ➔ Restriction point R (G1 – to - S transition): - commitment is made to DNA replication and subsequent cell division
➔ S
- Replication of cell’s DNA
- Two sister chromatids joined together and awaiting segregation into two new cells ➔ G
- Separates the end of S phase and the beginning of mitosis
- Cell gets bigger ➔ M phase
- Mitosis and cytokinesis Protein kinase is an enzyme that catalyzes the transfer of a phosphate group from ATP to a target protein
Cyclin-Dependent Kinases (Cdks)
➢ Need to be activated by binding to a second type of protein, called cyclin ➢ Protein on which the progress through the cell cycle depends ➢ Act at cell cycle checkpoints, points at which a cell cycle’s progress is regulated ● For DNA damage, there are three checkpoints: → During G1, before the cell enters S phase (restriction point) → During S phase → After S phase, during G
Yeast ➔ When the protein doesn’t work, it switches off the function of the mutated gene, then cell division doesn’t occur ➔ If you have a mutation in the gene - loss of function of the protein ➔ Normal yeast added to yeast mutants, put something of a normal yeast into a mutant yeast → can act normally again Cancer Cells ➔ With cancer you lose control over cell division (don't respond to growth factors) ➔ Cells divide continuously → form tumors ➔ Growth factors (oncogene proteins) are more sensitive, negative ➔ Regulators / inhibitors (tumor suppressors) are inactivated ➔ Can migrate to other locations in body (Metastasize) ➔ Cure by surgery or inhibiting cell cycle
What Is A Gene?
1) What are the Different Mendel Theories
Vocabulary:
- Character: an observable physical feature, such as flower color
- Trait: a particular form of a character, such as purple flowers or white flowers.
- Heritable trait: one that is passed from parent to offspring
- P: parental generation
- F1:first filial generation
- F2: second filial generation (plants were allowed to self-pollinate)
- Diploid: the two copies of each heritable unit in an organism
- Haploid: single set of heritable units
- Genome: The totality of all the genes of an organism
- Gene: Mendel’s unit of inheritance
- A sequence of DNA, resides at a particular site on a chromosome (locus / loci)
- Expressed in the phenotype mostly as proteins with particular functions, such as enzymes
- Dominant gene: can be thought of as a region of DNA that is expressed as a functional protein
- Recessive gene: typically expresses a nonfunctional protein, or a protein whose function is overshadowed by the dominant form
→ Dihybrid cross (cross of individuals that are identical double heterozygotes) → The alleles could maintain the associations they had in the parental generation (that is, they could be linked) → The segregation of S from s could be independent of the segregation of Y from y (that is, the two genes could be unlinked)
- Ratio:9:3:3:
- Recombinant phenotypes are new combinations
- Law Of Dominance → Some alleles are dominant while others are recessive; an organism with at least one dominant allele will display the effect of the dominant allele
2) Explain the ABO system
Three alleles for this gene ➔ O can only receive O ➔ AB can receive everything, can’t give any away ➔ A can receive A and O ➔ B can receive B and O ➔ Most important blood type system in human blood transfusion ➔ The associated anti-A and anti-B antibodies are usually IgM antibodies, which are produced in the first years of life by sensitization to environmental substances, such as food, bacteria, and viruses ➔ Blood groups are inherited from both parents
➔ Controlled by a single gene (the ABO gene) with three types of alleles inferred from classical genetics: i I A I B ➔ The gene encodes a glycosyl transferase (enzyme that modifies the carbohydrate content of the red blood cell antigens) ➔ The gene is located on the long arm of the ninth chromosome (9q34). ➔ The I A allele gives type A ➔ I B gives type B ➔ i gives type O ➔ As both IA^ and IB^ are dominant over i, only ii people have type O blood ➔ Individuals with IA^ IA^ or IA^ i have type A blood ➔ Individuals with I B I B or I B i have type B ➔ I A I B people have both phenotypes, because A and B express a special dominance relationship: codominance, which means that type A and B parents can have an AB child ➔ A couple with type A and type B can also have a type O child if they are both heterozygous (IB^ i, IA^ i) ➔ The cis-AB phenotype has a single enzyme that creates both A and B antigens ➔ The resulting red blood cells do not usually express A or B antigen at the same level that would be expected on common group A1 or B red blood cells, which can help solve the problem of an apparently genetically impossible blood group
➢ Only a problem when the mother is RH – and child is RH + and second child is RH+ again ➢ The mother's body may make antibodies to the Rh antigens in the baby’s blood ➢ The mother has become sensitized and her antibodies may cross the placenta and attack the baby’s blood ( attack breaks down the fetus’s red blood cells, creating anemia (a low number of red blood cells) ➢ Leads to hemolytic disease or hemolytic anemia.
4) What is the HLA Gene System?
● The human leukocyte antigen (HLA) system is the locus of genes that encode for proteins on the surface of cells, responsible for regulation of immune system ● Resides on chromosome 6 ● Encodes cell-surface antigen- presenting proteins and has many other functions ● The HLA genes are the major histo compatibility complex (MHC) genes of humans ● Histology is thestudy of tissues ● Will produce antibodies against antigens ● HLAs corresponding to MHC class I (A, B, and C) present peptides from inside the cell. For example, if the cell is infected by a virus, the HLA system brings fragments of the virus to the surface of the cell so that the cell can be destroyed by the immune system. These peptides are produced from digested proteins that are broken down in the proteasomes
● These particular antigens stimulate the multiplication of T- helper cells, which in turn stimulate antibody- producing B-cells to produce antibodies to that specific antigen
5) What is the Difference between the Classical & 21
st
Century Model?
➢ 21 st^ century model- description and knowledge of DNA ➢ Mendel was not aware of DNA and chromosomes
