Topic 2B - Part 2

Question 1

how does gene regulation in multicellular eukaryotes lead to cell specialization?

Answer 1

different types of cells express different genes

Question 2

what is the first level of control in gene regulation?

Answer 2

the chromosome (before transcription takes place)

Question 3

how does the chromosome level of control regulate gene expression?

Answer 3

the manner in which DNA is packaged can determine whether proteins necessary for transcription can gain physical access to the genes they transcribe

Question 4

chromatin

Answer 4

a complex of DNA, RNA, and proteins that gives chromosomes their structure; chromatin fibres are either 30nm in diameter or, in a relaxed state, 10 nm

Question 5

chromatin remodelling

Answer 5

the process in which the nucleosomes are repositioned to expose different stretches of DNA to the nuclear environment

Question 6

can transcription proteins access DNA when chromatin is in its coiled state?

Answer 6

no

Question 7

how is chromatin remodelled?

Answer 7

by chemical modification of the histones around which DNA is wound (usually histone tails)

Question 8

histone tail

Answer 8

a string of amino acids that protrudes from a histone protein in the nucleosome

Question 9

histone code

Answer 9

the pattern of modifications of the histone tails that affects the chromatin structure and gene transcription

Question 10

what are the typical modifications of the amino acid lysine in the histone tail during histone modification?

Answer 10

additional of a methyl group (methylation) or acetylation (COCH3)

Question 11

what is a common chemical modification to bases in DNA to regulate gene expression?

Answer 11

addition of a methyl group to cytosine

Question 12

DNA methylation (ex. modification to base) recruits proteins that affects changes in:

Answer 12

chromatin structure, histone modification, and nucleosome positioning that restrict access of transcription factors to gene promoters

Question 13

CpG Island

Answer 13

a cluster of CpG sites on a DNA strand where cytosine (C) is adjacent to guanosine (G) the ‘p’ represents the phosphate in the backbone; where cytosine methylation often occurs

Question 14

heavy cytosine methylation is associated with:

Answer 14

transcriptional repression of the gene near the CpG island

Question 15

undermethylated CpG islands allow:

Answer 15

transcription

Question 16

heavy methylated CpG islands result in:

Answer 16

inhibition of transcription

Question 17

epigenetic

Answer 17

describes effects on gene expression due to differences in DNA packaging; such as modifications in histones or chromatin structure

Question 18

epigenetic mechanisms typically do not involve changes to:

Answer 18

DNA sequence itself, rather to the manner in which DNA is packaged

Question 19

can epigenetic modifications be inherited?

Answer 19

yes, but they are often reversible and responsive to changes in the environment

Question 20

imprinting

Answer 20

the sex-specific silencing of gene expression

Question 21

for most genes, there is a direct relationship between:

Answer 21

the number of copies of the gene (gene dosage) and the level of expression of the gene

Question 22

each copy of the gene is regulated ________ of other genes

Answer 22

independently

Question 23

dosage compensation

Answer 23

the differential regulation of X-chromosomal genes in females and in males (regulation of genes in the X chromosome is different in females and males)

Question 24

X-inactivation

Answer 24

the process in mammals in which dosage compensation occurs through the inactivation of one X chromosome in each cell in females

Question 25

how does X-inactivation work?

Answer 25

a X chromosome contains the X-chromosome inactivation centre (XIC) which contains a gene Xist (X-inactivation specific transcript), Xist increases when X chromosome about to become inactive. transcript undergoes RNA splicing, Xist RNA coats the XIC region, coating spreads until entire chromosome is coated with Xist RNA which recruits factors that are associated with transcriptional repression

Question 26

Xist RNA is an example of a:

Answer 26

noncoding RNA

Question 27

if Xist gene is inserted into another chromosome…

Answer 27

that chromosome becomes inactivated

Question 28

transcriptional regulation

Answer 28

the mechanisms that collectively regulate whether or not transcription occurs

Question 29

what is the first point in transcription which regulates gene expression?

Answer 29

the recruitment of general transcription factors and components of the RNA polymerase complex (through the regulatory transcription factors)

Question 30

regulatory transcription factor

Answer 30

a protein that recruits the components of the transcription complex to the gene

Question 31

if the regulatory transcription factors do not recruit the components of the transcription complex to the gene,

Answer 31

transcription does not occur

Question 32

silencers

Answer 32

DNA sequences that bind with regulatory transcription factors and repress transcription

Question 33

if regulatory transcription factors bind with enhancers…

Answer 33

they stimulate transcription

Question 34

if regulatory transcription factors bind with silencers…

Answer 34

they repress transcription

Question 35

combinatorial control

Answer 35

regulation of gene transcription by means of multiple transcription factors acting together; a particular combination is needed of silencers/enhancers etc. to initiate transcription

Question 36

what is an opportunity for regulating gene expression in RNA processing?

Answer 36

RNA splicing-alternative splicing allows primary transcript to yield different proteins

Question 37

If exon 11 is missing in mRNA (ex. skeletal muscles):

Answer 37

cells form receptors with high insulin affinity

Question 38

If exon 11 is present in mRNA (ex. liver cells):

Answer 38

cells form receptors with low insulin affinity

Question 39

RNA editing

Answer 39

the process in which some RNA molecules become a substrate for enzymes that modify particular bases in the RNA, thereby changing it sequence and sometimes what it codes for

Question 40

what happens if the amino group is removed and converted to inosine in adenosine?

Answer 40

the base functions like guanosine

Question 41

what happens if the amino group is removed from cytosine?

Answer 41

it is converted to uracil

Question 42

what is the result of RNA editing?

Answer 42

transcripts from the same gene can product multiple types of proteins even in a single cell

Question 43

transcripts from the same gene may undergo different editing in different:

Answer 43

cell types (tissue specific)

Question 44

small regulatory RNA

Answer 44

a short RNA molecule that can block transcription, cleave or destabilize RNAA, or inhibit mrNA translation; two types: siRNA and miRNA

Question 45

small interfering RNA (siRNA)

Answer 45

a type of small double-stranded regulatory RNA that becomes part of a complex able to cleave and destroy single-stranded RNA with a complementary sequence

Question 46

microRNA (miRNA)

Answer 46

small, regulatory RNA micromolecules that can cleave or destabilize RNA or inhibit its translation

Question 47

siRNA and miRNA have different functions but similar:

Answer 47

forms of production; both are transcribed from DNA and form hairpin structures that are stabilized by base pairing

Question 48

RISC (RNA-induced silencing complex)

Answer 48

a protein complex that is targeted to specific mRNA molecules by base pairing with short regions on the target mRNA, inhibiting translation or degrading the RNA

Question 49

once small regulatory RNA is incorporated into RISC, depending on the type of small regulatory RNA, RNA sequence in RISC, and type of RISC, the small regulatory RNA may result in:

Answer 49

chromatin remodelling, degradation of RNA transcripts, or inhibition of mRNA translation

Question 50

regulation by small RNAs in eukaryotes is thought to have originated as:

Answer 50

a defence against viruses and transposable elements

Question 51

translation of mRNA into protein provides another level of:

Answer 51

control of gene expression

Question 52

almost all mRNA molecules contain:

Answer 52

a 5’ cap, a 5’ untranslated region, an open reading frame (containing codons that determine the amino acid sequence of the protein), a 3’ untranslated region, and a poly(A) tail

Question 53

the 5’ UTR and 3’ UTR (untranslated region) may contain:

Answer 53

regions that bind with proteins that help control mRNA translation and degradation, can also bind with small regulatory RNAs

Question 54

how do proteins specify the certain places in a cell where mRNA can be translated?

Answer 54

by transporting the mRNA to particular regions of the cell (through RNA-binding proteins on UTR regions) or through repressing translation of mRNAs in specific locations

Question 55

translation initiation is enhanced by:

Answer 55

poly(A) tail binding protein that brings the tail into contact with the initiation machinery on the 5’ cap-improves efficiency of translation initiation

Question 56

what is one of the main recognition signals for translation initiation?

Answer 56

the 5’ cap structure where the translation machinery assembles

Question 57

posttranslational modification

Answer 57

the modification, after translation, of proteins in ways that regulate their structure and function

Question 58

what are protein chaperones?

Answer 58

act as folding facilitators for proteins once they come off the ribosome-important for acquiring stability

Question 59

if folding is incorrect, protein may form:

Answer 59

aggregates that are destructive to cell function (ex. Alzheimer’s disease, Huntingdon’s disease)

Question 60

the effect of an intervention-genetic or environmental- at any given level can affect:

Answer 60

regulatory processes at both higher and lower levels because expression of any gene is regulated at multiple levels