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Biology > 7.2 > Flashcards

7.2 Flashcards

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1
Q

Where is the promoter located

A

at the 5’ end adjacent to the coding region

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2
Q

What are the three stages of transcription

A

initiation, elongation and termination

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3
Q

what happens during initiation

A

initiation starts when RNA polymerase binds to the DNA at the promoter region and the double helix unwinds

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4
Q

what happens during elongation

A

when mRNA becomes longer as nucleotides are added to the 3’OH group

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5
Q

what happens during termination

A

the mRNA synthesis is complete and the complex of DNA, RNA polymerase and mRNA disassembles

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6
Q

what happens when RNA polymerase has attached to the promoter

A

DAN separates at one end while it synthesizes a complementary RNA copy from the antisense DNA strand

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7
Q

what is the DNA template strand

A

the antisense strand

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8
Q

what lines up to the antisense strand

A

ribonucleoside triphosphate line up opposite to their exposed counterpart according to complementary base paring rules

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9
Q

what happens after ribonucloside triphosphates have lines up to their exposed counterparts

A

RNA polymerase forms covalent bonds between the growing mRNA molecule and the ribonucleotides.

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10
Q

where does the energy needed to drive the reaction come from

A

when the bond with the two additional phosphate groups are broken

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11
Q

when does transcription end

A

when the RNA polymerase reaches a termination region of DNA, it just stops and then detaches from the DNA

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12
Q

what is the DNA strand that is not transcribed called

A

the sense strand

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13
Q

how is the mRNA different in prokaryotes to eukaryotes

A

there s no nucleus so it begins transcription immediately

however, in eukaryotes, the mRNA needs to be prepared for translation. this process is called post transcriptional modification of mRNA

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14
Q

what is post transcriptional modification of mRNA

A

when it is prepared for translation after transcription

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15
Q

why does post-transcriptional modification take place

A

because of the introns and exons in the eukaryotic genes. Introns are DNA sequences in eukaryotic genes that contain no coding information. Sometimes, they contain controlling sequences that regulate the transcription of the gene. Exons are the DNA sequences that code for a polypeptide

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16
Q

brief steps of modifying RNA for translation

A

transcription (synthesis of pre mRNA), addition of a 5’ cap and a poly A tail (which protects the mRNA molecule from degradation) and finally splicing, which involves removing (excising) the introns and joining (ligating) the exons to form mature mRNA

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17
Q

what is a spliceosome

A

a large ribunucleoprotein (RNP) complex made up of five small nuclear ribonucleoproteins (snRNPS) and several proteins. It acts as an enzyme in the splicing process to remove introns and bind exons together.

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18
Q

what does the splicing of introns involve

A

spliceosome

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19
Q

steps of how spliceosome removes introns and joins exons to form mature mRNA

A
  1. snRNP forms base pairs with the ends of introns

spliceosome and looped intron form

intron is excised

exons are ligated, spliceosome disassembles

mature mRNA

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20
Q

what does splicing allow for

A

several proteins to be synthesized from the same gene

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21
Q

what genes have more exons

A

tropomyosin has 11 exons

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22
Q

how many forms of the protein scan b made from genes due to alternative splicing

A

at least five forms of protein

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23
Q

where does post transcriptional regulation not take place

A

in prokaryotes

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24
Q

Gene expression might be altered at the level of post-transcriptional processing in eukaryotes and not in prokaryotes because?

A

eukaryotic exons may be spliced in alternative patters

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25
Q

What is removed from pre-RNA to form mature eukaryotic mRNA?

A

introns

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26
Q

What is removed from pre-RNA to form mature eukaryotic mRNA?

A

introns

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27
Q

what direction does transcription occur

A

5 prime to 3 pime

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28
Q

what does the promoter do

A

it directly affects transcription by controlling whether or not RNA polymerase can access the gene

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29
Q

what is an operon

A

an operon is a set of genes all linked to a single promoter.

30
Q

what is an operator

A

a sequence of DNA in prokaryotes that allows a cell to regulate whether a gene is transcribed or not. this stops the binding of RNA polymerase with the promoter

31
Q

what is a lac operon

A

a group of genes/ operon with a single promoter

32
Q

regulatory proteins

A

these can increase the rate of transcription or decrease it

positive transcription factor or negative transcription factor

33
Q

where are operon usually found

A

usually in prokaryotes but can occur in eukaryotic

34
Q

RNA polymerase

A

starts transcription, needs a promoter

35
Q

what does RNA polymerase need to start transcription

A

a promoter

36
Q

what is an operator

A

a part of the DNA, a repressor can bind to it

37
Q

what happens if a repressor binds to the operator

A

it stops RNA polymerase from moving forward and making mRNA.

38
Q

name an example of regulating transcription

A

a lac operon
three genes involved with lac operon, enzymes

bacteria want lactose

lacI codes for the repressor
lacI is also bound to a promoter

39
Q

what happens if lactose is not present with the lac operon

A

if lactose is not present, the repressor binds to the operator, blocking mRNA polymerase, proteins cannot be created

40
Q

what happens if lactose is present with the lac operon

A

if lactose is present, it binds to the repressor, changing the conformation of the repressor and can no longer bind to the operator, polymerase can then carry on and make mRNA. the mRNA then can make enzymes to break down the lactose sugar and the cycle continues

41
Q

what does transcriptional regulation ensure

A

that certain genes are transcribed and other remain silent meaning that they are not transcibred

42
Q

what do activator proteins bind to

A

enhancers

43
Q

what do repressor proteins bind to

A

silencers

44
Q

what are enhancers and silencers examples of

A

non-coding regions of DNA with specific functions

45
Q

In response to the presence of certain food sources, prokaryotes can do which of the following?

A

alter the level of transcription of certain genes

46
Q

transcription regulation

A

allows the cell to produce proteins only needed at the time

is highly efficient at completely preventing transcription

can be controlled by repressor proteins

47
Q

what is not a DNA sequence to which proteins can bind in order to regulate gene expression

A

a repressor

48
Q

what are two additional ways of regulating transcription

A

involve small chemical changes to both histones and DNA

histones can be acetylated or methylated

49
Q

what chemical change can take place to DNA

A

it can be methylated

50
Q

what chemical changes can take place on histones

A

can be acetylated and methylated

51
Q

why do histones influence transcription

A

when they bind to DNA they Blick access to RNA polymerase

52
Q

what happens when histone proteins are activated

A

an acetyl group is added to the tails of histones proteins which prevents the bindings between nucleosomes. This partially unwinds the DNA allowing for enzymes involved in transcription to access it. As s result activation of histones generally keeps the genes active while deacetylation, removal of the acetyl group silences the gene

53
Q

what affect does acetylation of histones have

A

keeps the genes active

54
Q

what affect does deacetylation have on histones

A

silences the gene

55
Q

what happens when a histone is methylated

A

a methyl group is added, it can have a positive or negative effect on transaction depending on where the histones are located on the genome

56
Q

What is DNA methylation

A

when a methyl group is added to a cytosine found within a DNA molecule

57
Q

what plays a ole as a methyl donor

A

SAM

58
Q

what DNA base is methylated

A

cytosine

59
Q

what does cytosine become when it methylated

A

methylcytosine

60
Q

what generally happens when DNA is methylated

A

the DNA is usually not expressed as the nucleotides are shut down

61
Q

how long does mythelaticn last for

A

a long time

62
Q

what does methylation cause

A

the inactivation of the second X chromosomes in females for the duration of the life oft aha cell

63
Q

what is the level f DNA methylation of the genome associated with

A

diet, environmental conditions, age

64
Q

what is the study of epigenetic

A

the study of heritable changes in organisms that are brought abotu by changes in gene expression rather than by modification of the genetic code

65
Q

what happens if epigenetic change

A

the DNA sequence itself is not altered but some of the bases are altered

66
Q

epigenesis in mice; influence of a methylated food source on coat color

A

mice coats can be dark or yellow depending on the methylation of the gene for this trait.

when methylated, the coat color is brown, when not methylated, the gene I active and the coat is yellow

exposing mice during pregnancy t a diet high in folic acid (contains methyl) increased the proportion of dark mice in their litters.

indirect evidence that increased methylation of genes in the fetus can influence the inheritance of a trait

67
Q

what happens to methylation during DNA replication

A

it does not change

68
Q

what is produced during transcription

A

all types of RNA

69
Q

where does transcription take place in eukaryotes

A

in the cell nucleus

70
Q

What is the name of the non-coding section of DNA to which the RNA polymerase binds to initiate transcription

A

promoter

Biology (51 decks)

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