Lecture 7 - Genes & Their Expression

Question 1

gene expression:

Answer 1

“the information encoded by a gene is used in a functional manner”

Question 2

what percentage of genes are coding in the human genome?

Answer 2

only 1%

Question 3

what is the most common RNA found in our cells?

Answer 3

tRNA and rRNA (ribosomal)

Question 4

gene:

Answer 4

“DNA sequence that is the template that encodes information for a functional product made of RNA or protein”

Question 5

gene products contain:

Answer 5

both RNA and protein - but not all RNA becomes protein

Question 6

RNA is critical player in gene expression:

Answer 6

being a key information molecule, an important regulator of gene expression, and being critical for the synthesis of protein

Question 7

first step gene expression can be controlled:

Answer 7

transcription

Question 8

what controls initial gene expression specifically?

Answer 8

segments of DNA around a gene control its expression by regulating the activity of RNA polymerase II, which is responsible for generating the RNA molecule

Question 9

structure of a bacterial gene:

Answer 9

relatively simple structure:
- promoter region
- transcriptional terminator site
- transcriptional start site

(terminator and start site is NOT the same as stop and start codons)

Question 10

promoters:

Answer 10

the promoter is a sequence of the DNA where RNA polymerase binds to the DNA to synthesise the RNA transcript

comes before the gene itself, important in directing RNA polymerase to which strand of DNA they should bind and transcribe

Question 11

what can help the promoter region and where is it found?

Answer 11

sometimes, there is an UP element further upstream of the gene that is rich in thymine that helps to strengthen the promoter region

Question 12

what can deviations in the ‘UP Element’ cause?

Answer 12

deviations from these sequences impairs the binding of RNA polymerase to the promoter and affects gene expression

Question 13

operators:

Answer 13

• structural feature specific to prokaryotes
• either within the promoter or between the promoter and the target gene
• they are a binding sequence in which a repressor protein can bind which can physically stop RNA polymerase binding

Question 14

termimation sequence:

Answer 14

• signal that tells RNA polymerase to stop transcribing
• these are a sequence which creates a hairpin that matches which causes the stalling of the RNA polymerase

Question 15

do genes overlap in prokaryotes/bacteria?

Answer 15

genes rarely overlap in bacterium

Question 16

Most of the time, there is ___ _____ between the promoter and termination site

Answer 16

one gene

Question 17

monocistronic gene:

Answer 17

gene between the promoter and termination site - producing one mRNA transcript that makes one protein

Question 18

polycistronic genes:

Answer 18

where there are multiple genes between one promoter and a termination site - still making only one mRNA transcript, but one that can produce multiple proteins

Question 19

what do polycistronic genes allow for in bacteria?

Answer 19

polycistronic genes allows for a coordinated expression of multiple genes in the same pathway and often occurs with enzymatic pathways

Question 20

how is the structure in bacterial gene expression?

Answer 20

genes in bacteria have a simple but effective structure to control gene expression

Question 21

Both the promoter and terminator sites have _________ _________which are common and are important for the initiation and termination of transcription

Answer 21

consensus sequences

Question 22

how are eukaryotic genes similar to bacterial genes but also different?

Answer 22

they both have things such as promoter regions but there are greater levels of complexity in eukaryotic genes which adds additional levels of regulation

Question 23

how do we transcribe type II genes?

Answer 23

using RNA polymerase II

Question 24

function of the TATA Box:

Answer 24

involved in positioning the RNA polymerase correctly at the promoter and is similar to pribnow boxes in bacteria

Question 25

what actually is a TAT Box?

Answer 25

a sequence about 25 upstream of the transcription start site that has the sequence TATAAAA

Question 26

what can be found in the space beyond the TATA box?

Answer 26

there are a range of upstream control elements with common sequences:
–CAAT box with the sequence GGCCAATCT
–GC box with GGGCGG

Most eukaryotic genes have one of these and act as sites in which general transcription factors can bind

Question 27

general transcription factors:

Answer 27

general transcription factors are proteins that help with the recruitment and positioning of RNA polymerase II

Question 28

two effects regulators can have on gene expression:

Answer 28

–Enhancers can promote gene expression
–Silencers can inhibit gene expression

•Both of these play crucial roles in regulating gene expression and ensuring the right genes are expressed when needed in the right cells

•Sometimes, there are enhancers and silencers sequences occupying the same space that compete with each other to regulated gene expression

Question 29

what is meant when regulators are referred to as being ‘trans-acting’?

Answer 29

their regulatory sequences operate hundreds to thousands of nucleotides away from the gene itself

Question 30

why are bacterial regulators referred to as being ‘cis-acting’?

Answer 30

in bacteria they are cis-acting as they are right next to the promoter

Question 31

the upstream control elements binds general transcription factors which:

Answer 31

recruits the mediator complex which can then interact with the proteins binding to the regulators significantly further upstream along the DNA

Question 32

how can specialised proteins increase the association of a gene with a regulator?

Answer 32

specialized proteins can also hold eukaryotic chromosomal DNA in loops, which increases the association of a gene with a regulator like an enhancer or repressor

Question 33

why are there very little genes found in the telomeres and centromeres, where lists of chromatin is found?

Answer 33

there are very little genes because it is not efficient to keep unwinding to allow for gene expression, and could compromise chromosome integrity

Question 34

insulators:

Answer 34

Insulators are cis-acting elements that essentially act as ensuring that genes that other genes and/or chromosomal structure do not interfere with gene expression

•Insulators can block enhancers from working from neighbouring genes from interacting with promoters

•They can also act as a barrier against heterochromatin from encroaching into the euchromatin and repressing gene expression.

Question 35

eukaryotic genes have two non-coding regions in their coding regions:

Answer 35

– Exons are the part of the gene that code for the amino acid sequence for proteins

– Intros are the part of the gene that do not code for proteins and are between introns, but can play important regulatory roles

Question 36

bacteria + introns & exons?

Answer 36

Bacteria do not have introns and exons – the coding region of bacterial genes are generally uninterrupted

Question 37

Genes often controlled by many regulators – ensure genes are expressed:

Answer 37

–at the right level
–in the right cell
–in response to the right conditions
–at the right time.