● Base pairing of codon & anticodon at the ribosome results in
specific amino acids brought to the site of protein synthesis
● mRNA is read in 5’ => 3’ direction
● Translation ends when the
ribosome reaches a stop
codon on mRNA
1. 1st tRNA at the P site
2. 2nd codon of mRNA pairs w/
tRNA carrying 2nd amino acid
at A site
3. Ribosome moves along mRNA
until 2nd tRNA is at P site. (1st
tRNA is now at E site & later
DNA replication
released)
● A-T; C-G
4. Reaches stop codon & tRNA is
● Replicate bidirectionally
released & ribosome comes apart
1. 1 strand serves as template for 2nd second
5. Released polypeptide forms new protein
2. Topoisomerase & gyrase relax the strands
● In bacteria, translation can begin before transcription is complete
3. Helicase separates the strands & creates replication fork
Extrons & Introns
4. DNA polymerase adds complementary nucleotides to the 2 new
● Exons = regions of DNA that code for proteins
DNA strand
● Introns = regions of DNA that DO NOT code for protein
● New double-stranded DNA molecule contains 1 original & 1
● Small nuclear ribonucleoproteins (snRNPs) = remove introns &
new strand = semiconservative
splice exons together
● DNA is synthesized in one direction designated 5’ => 3’
● After modification, mature mRNA travels to cytoplasm where it
5. Leading strand = synthesized continuously
directs protein synthesis
6. Lagging strand discontinuous (Okazaki fragments)
Pre-Transcriptional Control
7. DNA polymerase = removes RNA primers; proofreads new DNA &
● Repression = inhibits gene expression & decreases enzyme
removes mismatched bases before DNA synthesis
synthesis; mediated by repressors (proteins that block
8. Okazaki fragments are joined by ligase
transcription); default is ON
Translations
● In repressible operons = structural genes are transcribed UNTIl they
● Translation = info in the nucleotide base sequence of mRNA is used
are turned off
for amino acid sequence of a protein
ex) corepressor tryptophan binds to repressor protein, activated
● Three-base codons of mRNA specify amino acids
, p y
repressor binds to operator & prevents transcription
● Specific amino acids are attached to molecules of tRNA. Another ● Induction = turn on gene expression; initiated by inducer; default is
portion of the tRNA has a base triplet called an anticodon
OFF
, ● In inducible operon = structural genes are not transcribed UNLESS ● When F factor becomes integrated into chromosome of F+ cell =>
inducer is present high frequency of recombination (Hfr) cell
ex) Lactose (inducer) binds to repressor; repressor cannot bind to
operator & transcription occurs
Transduction in Bacteria
● DNA is passed from 1 bacterium to another via bacteriophage;
incorporated into recipient’s DNA
● Generalized transduction = any bacterial genes can be transferred
● Specialized transduction = specific bacterial genes are transferred
Operon Model of Gene Expression
● Promoter = segment of DNA where RNA polymerase initiates
transcription of structural genes
● Operator = segment of DNA that controls transcription of structural
genes; gene expression
● Operon = set of operator & promoter sites & structural genes they
control
Conjugation
● plasmids transferred from 1 bacterium to another
● requires cell-to-cell contact
● When F factor (plasmid) is transferred from F+ to F-; F- cells are
converted to F+ cell
specific amino acids brought to the site of protein synthesis
● mRNA is read in 5’ => 3’ direction
● Translation ends when the
ribosome reaches a stop
codon on mRNA
1. 1st tRNA at the P site
2. 2nd codon of mRNA pairs w/
tRNA carrying 2nd amino acid
at A site
3. Ribosome moves along mRNA
until 2nd tRNA is at P site. (1st
tRNA is now at E site & later
DNA replication
released)
● A-T; C-G
4. Reaches stop codon & tRNA is
● Replicate bidirectionally
released & ribosome comes apart
1. 1 strand serves as template for 2nd second
5. Released polypeptide forms new protein
2. Topoisomerase & gyrase relax the strands
● In bacteria, translation can begin before transcription is complete
3. Helicase separates the strands & creates replication fork
Extrons & Introns
4. DNA polymerase adds complementary nucleotides to the 2 new
● Exons = regions of DNA that code for proteins
DNA strand
● Introns = regions of DNA that DO NOT code for protein
● New double-stranded DNA molecule contains 1 original & 1
● Small nuclear ribonucleoproteins (snRNPs) = remove introns &
new strand = semiconservative
splice exons together
● DNA is synthesized in one direction designated 5’ => 3’
● After modification, mature mRNA travels to cytoplasm where it
5. Leading strand = synthesized continuously
directs protein synthesis
6. Lagging strand discontinuous (Okazaki fragments)
Pre-Transcriptional Control
7. DNA polymerase = removes RNA primers; proofreads new DNA &
● Repression = inhibits gene expression & decreases enzyme
removes mismatched bases before DNA synthesis
synthesis; mediated by repressors (proteins that block
8. Okazaki fragments are joined by ligase
transcription); default is ON
Translations
● In repressible operons = structural genes are transcribed UNTIl they
● Translation = info in the nucleotide base sequence of mRNA is used
are turned off
for amino acid sequence of a protein
ex) corepressor tryptophan binds to repressor protein, activated
● Three-base codons of mRNA specify amino acids
, p y
repressor binds to operator & prevents transcription
● Specific amino acids are attached to molecules of tRNA. Another ● Induction = turn on gene expression; initiated by inducer; default is
portion of the tRNA has a base triplet called an anticodon
OFF
, ● In inducible operon = structural genes are not transcribed UNLESS ● When F factor becomes integrated into chromosome of F+ cell =>
inducer is present high frequency of recombination (Hfr) cell
ex) Lactose (inducer) binds to repressor; repressor cannot bind to
operator & transcription occurs
Transduction in Bacteria
● DNA is passed from 1 bacterium to another via bacteriophage;
incorporated into recipient’s DNA
● Generalized transduction = any bacterial genes can be transferred
● Specialized transduction = specific bacterial genes are transferred
Operon Model of Gene Expression
● Promoter = segment of DNA where RNA polymerase initiates
transcription of structural genes
● Operator = segment of DNA that controls transcription of structural
genes; gene expression
● Operon = set of operator & promoter sites & structural genes they
control
Conjugation
● plasmids transferred from 1 bacterium to another
● requires cell-to-cell contact
● When F factor (plasmid) is transferred from F+ to F-; F- cells are
converted to F+ cell
