Understanding Nucleic Acids: From Structure to Function, Exercises of Genetics

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Chapter 21

Nucleic Acids

Nucleic Acids Part 1: Introduction and Nucleotides (The Basic Building Blocks)

DNA:

RNA:

Function of DNA

RNA

Supporting Cast: Ribosomes

Red Blood Cells RBCs are produced from stem cells in the bone marrow. When RBCs mature, they discard their DNA to make room for more hemoglobin. Thus, they have no nucleus, no DNA, and do not divide. They produce energy through glycolysis, so RBCs do not have mitochondira.

What is glycolysis?

What important biochemical reactions occur in mitochondria?

N N

N N H

N N

N N

N

N

N N

N N

N N

N N

N N

N N

N N

N N

N N

N N

The Nitrogen Base

Derivatives of purine and pyrimidine

DNA Bases

RNA Bases

The Phosphate Group

Point an arrow to the bond that links the ribose to the phosphate group.

What type of bond links the phosphate group to the sugar?

Other important nucleotides

Construct AMP from its 3 basic parts: phosphate, adenine, & deoxyribose.

N N

N N

H (^) NH

deoxyribose

N N

O

O

H deoxyribose

N N

N N

O

N H H

H

deoxyribose

N N

N

O

H H

deoxyribose

DNA

DNA consists of two nucleic acid molecules twisted around each other to form a double helix.

Hydrophilic Backbone:

Hydrophobic Base Pairs:

Chromosomes: Higher Order DNA Structure

DNA is packaged into chromosomes found in the nucleus of cells

Chromosomes: highly compact structures containing DNA & proteins

Histones: proteins found in DNA

Nucleosomes: DNA wrapped around histones

Chromatin fiber: nucleosomes coiled upon themselves

Label the diagram below

DNA Replication Every person starts life as a fertilized egg (zygote) which contains the entire human genome. This single cell grows and divides to become a human being with one trillion cells – each with same genome as the zygote from which it originated.

DNA replication is an anabolic biochemical process.

1. Unravel super-coiled DNA to expose double helix

2. Each of the two strands is copied

Nucleic Acids Part 3: RNA and Protein Synthesis The genes in DNA hold the instructions for how to synthesize proteins.

The actual synthesis of the proteins requires RNA and ribosomes.

RNA – 3 Major Forms for 3 different jobs

rRNA

mRNA

tRNA

RNA is a single-stranded nucleic acid.

Ribosomes are the protein-making factories of the cell.

Transcription: Instructions from a section of DNA are copied to mRNA

Translation: tRNA delivers amino acids to the ribosome for protein synthesis

Translation: mRNA, tRNA & Protein Synthesis

Ribosomes are the cellular structures were the nucleotide sequence of the mRNA is read and a polypeptide is built by linking amino acids.

Codon: every group of three nucleotides on an mRNA molecule is known as a codon because it codes for one of the 20 amino acids.

Since there are 64 possible codons and only 20 amino acids, each amino acid has more than one codon.

Genetic Code: the key for the codons and their amino acids

tRNA – a closer look tRNA matches the codon on an mRNA with the corresponding amino acid

the cloverleaf shaped tRNA has two important regions

1. anticodon loop

2. 3’ end covalently bonded to the amino acid corresponding to the anticodon

Use the genetic code table to identify the amino acid attached to this tRNA.

Nucleic Acids Part 4: Genetic Mutations Any permanent chemical change at one or more nucleotides in the DNA sequence that affects the primary structure of a protein Substitution: a mutation caused by the substitution of a nucleotide Frameshift: a mutation caused by the deletion of a nucleotide Compare the altered genetic codes to the Normal Gene below and classify them as Substitution or Frame Shift.

Effects of DNA mutations are minimized by the fact that there is more than one codon for most amino acids.

DNA mutations can create defective enzymes. Some we can live with.

Some we can not.

Mutations are caused by a variety of factors: genetics, certain chemicals, high energy light (UV, X rays & gamma rays)

a)

Normal Gene

b)