ENVS 10

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ENVS 10

• Lecture 5
• DNA and Genetics

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Your genetic code

• DNA Deoxyribonucleic acid
• Genotype vs. phenotype
• DNA replication genotype
• Protein synthesis phenotype
• DNA is the genetic language
• Is encoded

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DNA and RNA Polymers of Nucleotides

• DNA and RNA are nucleic acids

• They consist of chemical units called nucleotides
• The nucleotides are joined by a sugar-phosphate
  backbone
• The order of the nucleotides is the genetic code

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Structure of DNA/RNA (cont)

• Nucleotides are found along strands of DNA or RNA
• Sugar-phosphate bonds (stable)
• Hydrogen bonds (weak)
• DNA is double-stranded
• RNA is single stranded

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Phosphate group
Nitrogenous base
Sugar
Nitrogenous base (A,G,C, or T)
Nucleotide
Thymine (T)
Phosphategroup
Sugar (deoxyribose)
DNA nucleotide
Polynucleotide
Sugar-phosphate backbone
Figure 10.2
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• The four nucleotides found in DNA

• Differ in their nitrogenous bases
• Are thymine (T), cytosine (C), adenine (A), and
  guanine (G)
• RNA has uracil (U) in place of thymine

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• The model of DNA is like a rope ladder twisted
  into a spiral

Twist
Figure 10.4
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• Detailed representations of DNA

• Notice that the bases pair in a complementary
  fashion

Hydrogen bond
Figure 10.5
(c)
(a)
(b)
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DNA Replication

• When a cell or organism reproduces, a complete
  set of genetic instructions must pass from one
  generation to the next
• Complementary bases can use both strands to make
  exact copies of original DNA information (same
  information but mirror images)

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• Watson and Cricks model for DNA suggested that
  DNA replicated by a template mechanism

Parental (old) DNA molecule
Daughter (new) strand
Daughter DNA molecule (double helices)
Figure 10.6
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DNA replication

• DNA makes an identical copy of itself
• Occurs in nucleus
• Prior to cell division (mitosis) or gamete
  production (meiosis)
• Uncoil, unzip, and copy
• Match complementary base pairs
• Need enzymes (DNA polymerase and others)

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Origin of replication
Origin of replication

• DNA replication

• Begins at specific sites on a double helix
• Proceeds in both directions

Origin of replication
Parental strand
Daughter strand
Bubble
Two daughter DNA molecules
Figure 10.8
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Protein Synthesis

• Expression of DNA
• Decodes the language of DNA (nucleotides) into
  the language of proteins (amino acids)
• Converts genotype to phenotype

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Basic processes in DNA expression

• DNA is transcribed into RNA
• RNA translated into proteins
• Proteins have functions
• Structure
• Carrier
• Enzymatic/hormonal

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Nucleus
DNA

• DNA specifies the synthesis of proteins in two
  stages

Transcription
RNA

• Transcription
• Translation

Translation
Protein
Cytoplasm
Figure 10.9
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• What is the language of nucleic acids?

DNA molecule
Gene 1
Gene 2
Gene 3

• In DNA, it is the linear sequence of nucleotide
  bases

DNA strand
Transcription
RNA
Codon
Translation
Polypeptide
Amino acid
Figure 10.10
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The Genetic Code

• The genetic code is the set of rules relating
  nucleotide sequence to amino acid sequence

Figure 10.11
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RNA polymerase
DNA of gene
Promoter DNA

• Transcription of an entire gene

Terminator DNA
Initiation
RNA
Area shown in part (a)
Elongation
Termination
Growing RNA
Completed RNA
RNA polymerase
Figure 10.13b
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Review

• DNA ? RNA ? Protein
• Step 1 transcription (DNA ? RNA)
• Step 2 translation (RNA ? Protein)

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Mutations

• Changes in DNA sequence
• Point mutation single DNA nucleotide
• Missense
• Nonsense
• Frameshift
• Deletion
• Duplication
• Insertion

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Mutations

• A mutation

• Is any change in the nucleotide sequence of DNA

Normal hemoglobin DNA
Mutant hemoglobin DNA
mRNA
mRNA
Sickle-cell hemoglobin
Normal hemoglobin
Glu
Val
Figure 10.21
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• Although mutations are often harmful

• They are the source of the rich diversity of
  genes in the living world
• They contribute to the process of evolution by
  natural selection

Figure 10.23