Post on 11-Jan-2016
transcript
Chapter 10 – Gene Expression & Regulation
• What is gene expression?
• How do mutations in DNA affect proteins?
• How is gene expression regulated?
What is gene expression?
• The process of making proteins from the DNA nucleotide message of genes
• Also called protein synthesis
Gene expression (protein synthesis) is a two-step process
•
Transcription – making a portable RNA copy of a gene
messenger
RNA vs. DNA
Transcription copies the template strand of a gene
• DNA: TACGCCACTAAT
• AUGCGGUGAUUAAUGCGGUGAUUA
ATGCGGTGA TTAATGCGGTGA TTA
mRNA:mRNA:Replication:Replication:
Transcription: RNA polymerase copies a gene’s nucleotide sequence into an mRNA sequence
promoter sequence (example: TATAAT)promoter sequence (example: TATAAT)Transcription animation back-up link
Transcription: RNA polymerase stops transcribing at the end of a gene
Termination sequenceTermination sequence
Gene expression (protein synthesis) is a two-step process
Translation – synthesizes a polypeptide (protein) according to the nucleotide sequence information of a mRNA molecule
Codons – triplets of mRNA nucleotides, each Codons – triplets of mRNA nucleotides, each specifying a particular amino acidspecifying a particular amino acid
CFTR gene sequence
Translation utilizes specific codon sequences to begin and end protein synthesis
Template strandStart and stop Start and stop
codonscodons
CFTR gene sequence
Translation is accomplished by ribosomes
Translation utilizes transfer RNA molecules to carry specific amino acids to the ribosomes
• tRNA anticodon – complementary to an mRNA codon
Translation uses complementary base pairing between mRNA codons and tRNA anti-codons
RibosomeRibosome
mRNAmRNA
tRNAstRNAs
The process in which the DNA sequence of a gene is copied into mRNA is called
1)DNA replication
2)mRNA replication
3)RNA polymerase
4)Translation
5)Transcription
1. The location on RNA where RNA polymerase binds and initiates transcription.
2. It is a component of each type of RNA.
3. The location where ribosomes bind to the DNA.
4. The location on the DNA template strand where RNA polymerase binds and initiates transcription.
5. The location where ribosomes bind to the mRNA.
What is the promoter region of a gene?
Transcription of the DNA sequence ATCGATA would be
1)TAGCTAT
2)AUCGAUA
3)TUGCTUT
4)UUGCUUU
5)UAGCUAU
1. ATG
2. AUG
3. UAC
4. TAC
5. TUG
Imagine that the template strand of a gene has the sequence TAC. What sequence of the anticodon would
decode this?
Ribosomes
1)Translate mRNA molecules in the nucleus of the cell
2)Bind to the promoter sequence of a mRNA to initiate translation
3)Contain anti-codons which match specific mRNA codons
4)All of these5)None of these
How do mutations in DNA affect proteins?
• Nucleotide substitutions
• Nucleotide deletions
• Nucleotide insertions
A
T
A
tryptophan
A
How do mutations in DNA affect proteins?
A single amino acid substitution at position 269
CAA changed to CCA
Glutamine to proline
How do mutations is DNA affect protein?
• MP and the 5alpha-reductase-2 (SRD5A2) gene
How do mutations in DNA affect protein?
• FIG. 1. Mutations of the SRD5A2 gene. A, A heterozygous C78G transversion at exon 1, resulting in Tyr26Stop (Y26X) in case 1. B, A heterozygous G100C transversion at exon 1, leading to Gly34Arg (G34R) in case 2. C, A homozygous G680A transition at exon 4, causing
Arg227Gln (R227Q) in case 3. Link
How do mutations in DNA affect proteins?
• Nucleotide insertions and deletions shift the “reading frame” (how mRNA codons are translated)
Also called frameshift mutationsAlso called frameshift mutations
Insertions, deletions and frame shifts
• The fat cat ate the rat…
• Hef atc ata tet her at…
• ExampleTAC GCG GAT CGA…TAC GCG GAT CGA…
TAC GCG ATC GAn…TAC GCG ATC GAn…AUG CGC AUG CGC UAGUAGTranscribe:Transcribe:
• Werner’s syndrome
• Cystic fibrosis
Mutations and genetic disease
Myostatin gene mutation
• 11 bp deletion
How is gene expression regulated?
• Control can happen at several points in the process
• Control to turn on/turn off protein production
• Control amount of protein production
How is gene expression regulated?
• Transcriptional regulation involves regulatory “repressor” and/or “activator” molecules
• Transcription factors – molecules required to promote binding of RNA polymerase to a gene promoter
How is gene expression regulated?
• mRNA is “silenced” by RNA interference (RNAi)
• siRNA molecules (small interfering RNAs) are double stranded RNA molecules that when activated, degrade (cut up) specific mRNA molecules, silencing gene expression
A frameshift mutation
1. Occurs when an incorrect nucleotide is substituted for the correct one somewhere in the DNA sequence of a gene
2. Occurs whenever nucleotides are inserted or deleted from a DNA sequence of a gene
3. Occurs when any change is made in the nucleotide sequence of a gene
A transcription factor
1. Promotes gene expression by facilitating the binding of RNA polymerase to mRNA
2. Inhibits gene expression by preventing RNA polymerase from binding to mRNA
3. Silences mRNA by cutting it up
4. Prevents mRNA from being transcribed into a protein
Which of the following regulate gene expression post-transcriptionally?
1.Transcription factors
2.Repressor proteins
3.RNA interference
4.All of these