introduction to molecular regulation and signalling

Question 1

what is a placode?

Answer 1

a local thickening in the embryonic ectoderm that develops into a sensory organ or ganglion

Question 2

how is embryonic development directed?

Answer 2

by genomes containing all info needed to make an individual

info encoded in DNA in sequences called genes coding for proteins

proteins regulate expression of genes and act as signal molecules

Question 3

how many genes are there in the human genome?

Answer 3

23000 approx

Question 4

at what levels can gene expression be regulated?

Answer 4

different genes may be transcribed

DNA transcribed from a gene may be selectively processed to regulate which RNAs reach the cytoplasm to become mRNAs

mRNAs may be selectively translated

proteins made from mRNA may be differentially modified

Question 5

what is a nucleosome composed of?

Answer 5

octamer of histone proteins

140 base pairs DNA

Question 6

how are nucleosomes joined?

Answer 6

into clusters by binding of DNA existing between histones (linker DNA) with other histone proteins (H1 histones)

Question 7

what is the function of nucleosomes?

Answer 7

to keep the DNA tightly coiled, so it can’t be translated

Question 8

regions of genes on DNA strand

Answer 8

exons - regions which can be translated into proteins

introns - regions which can’t be translated into proteins

Question 9

what does a typical gene include?

Answer 9

exons and introns

promoter region

transcription initiation site

translation initiation site

translation termination codon

3’ untranslated region

Question 10

what does the promoter region do?

Answer 10

binds RNA polymerase for the initiation of transcription

Question 11

what does the translation initiation site do?

Answer 11

designates first amino acid in protein

Question 12

what does the 3’ untranslated region contain/do?

Answer 12

poly A addition site assists with stabilising mRNA, allows it to exit the nucleus and translates it into a protein

Question 13

TATA box

Answer 13

sequence TATA

to bind to this, the RNA polymerase needs additional factors called transcription factors

Question 14

what are transcription factors and what do they do?

Answer 14

proteins with a specific DNA binding domain and a transactivating domain which activates/inhibits transcription of the gene whose promotor/enhancer it’s bound to.

with other proteins they activate gene expression by unwinding DNA nucleosome complex - releases polymerise to transcribe DNA template and prevents new nucleosomes from forming

Question 15

what are enhancers?

Answer 15

regulatory elements of DNA that activate utilisation of promoters to control their efficiency and rate of transcription from promoter

bind transcription factors

regulate timing of expression and cell-specific location

Question 16

where can enhancers be located?

Answer 16

anywhere along strand

don’t have to be close to a promoter

Question 17

example of a transcription factor

Answer 17

PAX6

pancreas, eye and neural tube development

contains 3 separate enhancers, each regulating gene’s expression in appropriate tissue

Question 18

how do enhancers act?

Answer 18

altering chromatin to expose the promoter or by facilitating binding of RNA polymerase

Question 19

what are silencers?

Answer 19

enhancers inhibiting transcription

allows a transcription factor to activating one gene and silence another by binding to different enhancers

Question 20

what is a mechanism that silences genes?

Answer 20

methylation of cytosine bases in the promotor regions of genes represses their transcription

Question 21

X chromosome inactivation

Answer 21

one chromosome in each xx pair is inactivated due to the methylation of cytosine bases

Question 22

how does this affect the differentiation of cells?

Answer 22

genes in different types of cells are repressed by methylation

Question 23

genomic imprinting

Answer 23

due to DNA methylation - only a gene from the mother/father is expressed, and the other is silent

40-60 human genes imprinted

Question 24

how does methylation silence DNA

Answer 24

inhibits binding of transcription factors

altering of histone binding -> stabilisation of nucleosomes, tightly coiled DNA that can’t be transcribed

Question 25

what is the original transcript of a gene called?

Answer 25

nuclear RNA or premessenger RNA

longer than mRNA because it contains introns that are spliced as it moves from nucleus to cytoplasm (different proteins from a single gene)

Question 26

what does splicing allow?

Answer 26

different proteins to be produced from a single gene - exons spliced in different patterns (alternative splicing)

carried out by spliceosomes - complexes of small nuclear RNAs (snRNAs) and proteins that recognise specific splice sites at 5’ or 3’ ends of nRNA.

Question 27

what are spliceosomes?

Answer 27

carry out splicing

complexes of snRNAs and proteins that recognise specific splice sites at 5’ or 3’ ends of nRNA.