Lecture 18 - Introduction to control of gene expression

Question 1

Genome (4)

Answer 1

Human genome contains 50000 genes.
Only 10000 genes are expressed.
Genome is identical in every cell.
Must be differentially interpreted in diff cells at diff times.

Question 2

Genotype (1)

Answer 2

Human cells all contain the same genetic blueprint.

Question 3

Differential gene expression is tightly regulated in…. (3)

Answer 3

Time
Development , embryo/adults
In response to hormones, infections

Space
Diff tissues/cell types express diff genes (brain vs muscles)

Question 4

Failure to regulate gene expression tightly may lead to… (4)
DNA –> RNA –> Proteins

Answer 4

Metabolism –> Metabolic disease (e.g. diabetes).
Cell shape/motility –> Metastasis.
Cell differentiation –> Congenital disorders (e.g. drosophila).
Cell proliferation –> Cancer.

Question 5

Drosophila homeotic mutants (5)

Answer 5

BX-C (Bithorax complex- type of homeotic gene) controls the differentiation of abdominal/posterior thoracic segments.
Located on chromosome III.
Genes mutate and the third thoracic segment creates a ‘second thorax’ –> 2nd pair of wings/stomach.

Antennapedia (Antp) is a HOM-C gene - controls the formation of legs during development.
Loss of function mutations OR gain-of-function mutations convert antennae into ectopic legs.

Question 6

Differentiation from a single cell (2)

Answer 6

• Totipotent cells – only found in the zygote, can differentiate into any cell.
• Pluripotent- can form any tissues in body except placenta tissue.

Question 7

The big goal (2)

Answer 7

Isolate adult stem cells from all developmental compartments.
These cells develop in vivo or in vitro in a controlled manner so we can regenerate tissues.

Question 8

B-thalassaemia (3)

Answer 8

Insufficent expression of B globin gene..
The B globin gene is structurally normal, mutations in actual bases. Single base changes.
ATAAA –> ACAAA (T–> C)
CACaGCTCCT –> CACgGCTCCT ( A–> G)

Question 9

Examples of translational control (3)

Answer 9

Early embryogenesis - during first 4-8 cell divisions no gene expression. End of blastocyst formaton, first genes expresssed are from MATERNALLY-DERIVED PRE-FORMED mRNA.

Environmental stress - Exposure to heat shock/pathogens cause change in translation.

E.G. Ferritin (shows how much iron the body stores).

Question 10

Anatomy of Eukaryotic mRNA (4)

Answer 10

Frame is set by first codon - always AUG.
5’ UTR part of exon.
Kozak consensus sequence - major role in initiation of translation.
Sequence on mRNA molecule (recognised by ribosome) initiates translation.

Question 11

5’/3’ UTRs and control of gene expression (6)

Answer 11

5’ UTR - How efficiently the ribosome initiates translation.
Globin - Effectively translated.
Ferritin - Uneffectively translated.

3’ UTR - Stability on mRNAs.
Globin - Very stable.
Immune stress hormones - Very unstable.

Question 12

Ferritin (3)

Answer 12

Intracellular Iron levels are translationally controlled
Ferritin - binds Iron and retains in the cytoplasm as a store for excess.
Only need Ferritin at times of Iron excess.

Question 13

miRNAs (5)

Answer 13

500 small non-coding RNAs - micro RNAs.
Transcribed by RNA Polymerase II.
Control post-transcriptional regulation of about 1/3 of all human genes.
Regulates several target genes.
Targets a complementary mRNA molecule for destruction.

Question 14

Process of how miRNAs work (8)

Answer 14

precursor miRNA transcript –>
A double stranded intermediate –>
mature, single-stranded miRNA –>
assembles with a set of proteins into a complex - RISC –>
Searches for mRNAs that have a nucleotide sequence complementary (to its bound miRNA) –>
Depending on how extensive the region of complementarity is (more/less extensive match)
1) Rapidly degraded by a nuclease within the RISC.
2) Transferred to an area of the cytoplasm where other cellular nucleases destroy it.