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