19.01.04 gene structure

Question 1

Define gene

Answer 1

region of DNA used as template to synthesise functional complementary RNA molecule

Question 2

Two types of gene are:

Answer 2

• Coding - decoded to generate corresponding polypeptide sequence i.e. messenger RNA (mRNA)
• Non-coding - do not serve as templates for making polypeptides; help regulate expression of other genes

Question 3

Pseudogenes

Answer 3

non-functional inheritable genetic elements. - unable to produce functional proteins. - ~10,000 in mammalian genome (~20% are transcribed into RNAs).

Question 4

Number of pseudogenes in mammalian genome

Answer 4

~10,000

Question 5

Open reading frame (ORF)

Answer 5

sequence of successive nucleotide triplets read as codons specifying amino acids; begin with initiation (start) codon i.e. AUG (coding for methionine) and end with stop codon (i.e. UAA, UAG or UGA)

Question 6

Regulatory factors

Answer 6

required by RNA polymerase to initiate transcription of genes; divided into cis-acting (located on same DNA molecule as genes they regulate) and trans-acting (produced by remote genes - migrate to site of action)

Question 7

Cis-acting regulators

Answer 7

Promoter, enhancer, silencer, insulator

Question 8

Promoter

Answer 8

regulator region close to 5′ end of gene to which RNA polymerase binds in order to initiate transcription of gene; consists of core promoter and proximal and distal promoter elements

Question 9

enhancer

Answer 9

regulatory sequence; modulates rate of transcription of associated gene in response to binding of specific proteins (activators); located at variable distances from the TSS; DNA between promoter and enhancer loops out, bringing 2 sequences together

Question 10

silencer

Answer 10

sequence bound by repressors, inhibiting activators and reducing transcription; prevent gene expression during differentiation and progression through cell cycle

Question 11

insulator

Answer 11

sequence element that protects genes from inappropriate signals emanating from their surrounding environment either by blocking action of enhancer on promoter (if situated between them) or by acting as “barriers” that prevent advance of nearby condensed chromatin

Question 12

Trans-acting regulators

Answer 12

Transcription factors = proteins that control rate of transcription of DNA to mRNA, by binding to specific DNA sequences

Question 13

Post-transcriptional processing

Answer 13

RNA (primary) transcript of most eukaryotic genes (complementary to entire length of gene) undergoes series of processing reactions to make mature mRNA/non-coding RNA

Question 14

RNA splicing

Answer 14

series of reactions whereby intronic RNA segments (non-coding) are removed and discarded while remaining exonic RNA segments (coding) are joined end-to-end. Only central segment of mature mRNA molecule is translated to make polypeptide.

Question 15

5’ UTR

Answer 15

spans region from TSS to nucleotide before mRNA start site; binds ribosome (RNA-protein complex; provides structural framework for polypeptide synthesis. 10-18% of genes have alternative 5’UTRs. e.g. BRCA1

Question 16

3’ UTR

Answer 16

immediately follows translation termination (stop) codon; contains:

• terminator sequence (marks endpoint for transcription and releases RNA polymerase)
• regulatory regions - post-transcriptionally influence mRNA polyadenylation, translation efficiency, localization, and stability, and ultimately gene expression

Question 17

Mitochondrial genome transmitted exclusively through

Answer 17

the female germ line

Question 18

human mitochondrial DNA (mtDNA) structure

Answer 18

double-stranded, circular molecule of 16569 bp and contains 37 genes coding for two ribosomal rNAs (rRNAs), 22 transfer RNAs (tRNAs) and 13 polypeptides

Question 19

mitochondrial heavy- (G rich) and light chain (C rich) transcribed from

Answer 19

different promoter regions, in opposite directions

Question 20

Mitochondrial genes are

Answer 20

closely clustered and contain no introns