chapter 2 an introduction to genes and genomes. introduction to molecular biology
TRANSCRIPT
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Chapter 2Chapter 2
An Introduction to Genes and Genomes
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Introduction to Molecular Biology
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Prokaryotic Cell Structure
Prokaryotic Cell Eukaryotic Cell
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Eukaryotic Cell StructureEukaryotic Cell Structure
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Eukaryotic Cell StructureEukaryotic Cell Structure
Animal Cell Plant Cell
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Let’s in on a cell!
DNA Zoom Interactive
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DNA Discovery DNA Discovery (visit DNAi.org)(visit DNAi.org)
Miescher – identified a nuclear substance he called nuclein Griffith – performed the first transformation Avery, McCarty, and Macleod – identified Griffith’s
transforming factor as DNA Chargaff – proved that the percentage of the DNA bases
adenine always equaled thymine and guanine always equaled cytosine
Wilkins, Franklin, Watson & Crick – demonstrated the structure of DNA
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Structure of DNAStructure of DNA
• Deoxyribose Sugar
• Phosphate• Nitrogen Base
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Purines – double ring
Pyrimidines – single ring
Structure of DNAStructure of DNA
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Structure of DNA
Nucleic Acid Overview
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Structure of DNA
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DNA ReplicationDNA Replication
When DNA makes an exact copy of itself
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DNA ReplicationDNA Replication
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The first step in DNA
DNA ReplicationDNA Replication
replication is for the enzyme, helicase, to unzip the double stranded DNA molucule.
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DNA ReplicationDNA Replication
Proteins hold the two strands apart.An RNA primer lays down on each
strand of DNA.
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DNA polymerase extends the primer by adding complementary nucleotides.
DNA polymerase can only extend in the 5’ → 3’ direction
DNA ReplicationDNA Replication
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DNA ReplicationDNA Replication
Leading strand follows helicase. Lagging strand must wait for replication fork to
open and therefore forms discontinous Okazaki fragments.
Ligase seals the nicks in the DNA backbone between the Okazaki fragments. helicase
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Let’s put it all togetherLet’s put it all together
Click on the animation below.Select the button for the “whole
picture”.
DNA Replication Animation
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TranscriptionTranscription
Making an RNA copy from a DNA template
RNA polymerase
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RNA StructureRNA Structure
Uracil instead of thymine
Ribose sugar instead of deoxyribose sugar
Single strandedCan leave the nucleus
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RNA StructureRNA StructuremRNA – RNA copy of DNA that carries
genetic information from the nucleus to the ribosomes
rRNA – makes up the ribosomestRNA – carries amino acids to ribosomes
for protein synthesis
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Transcription
RNA polymerase binds to a promoter region on double stranded DNA and unzips the double helix.
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Transcription
Free RNA nucleotides pair with the complementary DNA of the template strand
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Transcription
RNA is processed Introns are spliced out 7 methyl guanosine cap Poly-A tail
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Transcription
mRNA leaves the nucleus and travels to the ribosomes in the cytoplasm
ribosome
nucleus
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Let’s put it all together
Transcription Animation
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Practice
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Central Dogma of Molecular Biology
Click to see Video
Animation
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Translation
Making protein from mRNA
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Translation
Important Definitions A codon is composed of
3 RNA nucleotides Each codon codes for
one amino acid Protein does the work in
a cell
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Translation
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Translation
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First Base Second Base
U C A G
U
U
C
A
G
phenylalanine
serine
tyrosine
cysteine
phenylalanine
serine
tyrosine
cysteine
Leucine
serine
(stop)
(stop)
Leucine
serine
(stop)
tryptophan
C
U
C
A
G
leucine
proline
histidine
arginine
leucine
proline
histidine
arginine
leucine
proline
glutamine
arginine
leucine
proline
glutamine
arginine
A
U
C
A
G
isoleucine
threonine
asparagine
serine
isoleucine
threonine
asparagine
serine
isoleucine
threonine
lysine
arginine
met (start)
threonine
lysine
arginine
G
U
C
A
G
valine
alanine
apartic acid
glycine
valine
alanine
apartic acid
glycine
valine
alanine
glutamic acid
glycine
valine
alanine
glutamic acid
glycine
Third Base
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Translation
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Translation
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Translation
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Translation
• Asparagine, Serine, Methionine
• Tryptophan, Glycine, Lysine
• Proline, Leucine, Serine• Aspartic acid, Histidine, Threonine
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Translation
Always begins at a start codon and ends at a stop codon.
The region between the start and stop codons is called the open reading frame (ORF)
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Practice
Click on the animation to transcribe and translate a gene.
Click to see animation
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Translation Initiation
mRNA attaches to the small subunit of a ribosome
tRNA anticodon pairs with mRNA start codon
Large ribosomal subunit binds and translation is initiated
tRNA anticodon
amino acid
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Translation Elongation
Anticodon of tRNA carrying next amino acid binds to codon on mRNA
A peptide bond joins the amino acids and the first tRNA is released.
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Translation Termination
Amino acid chain continues until a stop codon is read. The amino acid chain is released and all of the translation machinery is recycled to translate another protein.
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Let’s put it all together
Click on the animation below
Translation Video
Translation Animation
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Let’s put it all together
5’-GATCTGAATCGCTATGGC-3’
3’-CTAGACTTAGCGATACCG-5’
mRNA 5’-GAUCUGAAUCGCUAUGGC-3’
CUAGACUUAGCGAUACCG Asp, Leu, Asn, Arg, Tyr, Gly
Coding:
Template:
mRNA:
tRNA:
amino acid:
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Control of Gene Expression
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Control of Gene Expression
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Control of Gene Expression
Prokaryotes cluster genes into operons that are transcribed together to give a single mRNA molecule.
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Lac Operon Promoter region allows RNA polymerase to
attach and begin transcription. Operator region is in the middle of the
promoter.
Control of Gene Expression
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If a repressor protein is bound to the operator, RNA polymerase cannot pass to transcribe the genes.
Control of Gene Expression
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When the inducer (lactose) binds to the repressor protein, it changes shape and falls off of the operator region.
Now RNA polymerase can pass and transcribe the genes into mRNA.
Control of Gene Expression
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Let’s put it all together
Click on the animation below.
Video of lac operon
Animation of lac operon
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Mutations
Mutations are changes in the DNA sequence.
Mutations can be inherited or acquired.
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Mutations
Mutagens are agents that interact with DNA to cause mutations.
Examples are chemicals and radiation.
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Mutations
Point mutation changes a single base Point mutations can be silent, meaning they code
for the same amino acid.
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Mutations
Point mutations can also code for a structurally similar amino acid.
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Mutations
Point mutations are not always harmless. If the mutation occurs on a critical amino acid in the active
site of the protein, it can be detrimental, as in the case of sickle cell anemia.
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Mutations
Frameshift mutations cause a shift in the reading frame by adding or deleting nucleotides.
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Mutations
An example of a deletion causing a premature stop codon.
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Mutations