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IB Biology > 7.2 Transcription and gene expression > Flashcards

7.2 Transcription and gene expression Flashcards

1
Q

What is a gene?

A

A sequence of DNA which is transcribed into RNA

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2
Q

What are the three parts of a gene?

A

Promoter
Coding sequence
Terminator

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3
Q

What is the promoter?

A

The non coding sequence responsible for the initiation of transcription

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4
Q

Where is the promoter typically located?

A

Immediately upstream of the genes coding sequence

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5
Q

What does the promoter function as?

A

A binding site for RNA polymerase

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6
Q

What controls and mediates the binding of RNA polymerase to the promoter?

A

An array of transcription factors in eukaryotes

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7
Q

What do the transcription factors bind to?

A

Proximal or distal control elements

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8
Q

What is the coding sequence?

A

The region of DNA that is transcribed by RNA polymerase

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9
Q

What happens after RNA polymerase has bound to the promoter?

A

It causes the DNA strands to unwind and separate

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10
Q

What does the mechanism for transcriptional termination differ between?

A

Prokaryotes and eukaryotes

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11
Q

What stops RNA polymerase transcribing the DNA?

A

The terminator (sequence)

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12
Q

How many strands does a gene have?

A

Two

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13
Q

How many strands are transcribed into RNA?

A

One

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14
Q

What is the antisense strand?

A

The strand that is transcribed into RNA

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15
Q

What is the sense strand?

A

The strand that is not transcribed into RNA

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16
Q

What is the sequence of the antisense strand complimentary to?

A

The RNA sequence

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17
Q

When will the antisense strand be the DNA version?

A

During the tRNA anticodon sequence

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18
Q

What is the antisense strand referred to as?

A

The template strand

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19
Q

When will the sense strand be the DNA verion?

A

In the RNA sequence

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20
Q

What else is sense strand referred to as?

A

The coding strand

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21
Q

Why is the determination of sense and antisense gene specific?

A

Either of the 2 polynucleotide strands may contain a gene

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22
Q

What is transcription?

A

The process where a DNA sequence is copied into a complementary RNA sequence by RNA polymerase

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23
Q

How do free nucleotides exist in cells as?

A

Nucleoside triphosphates

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24
Q

How do nucleoside triphosphates line up?

A

Opposite their complementary base partner

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25
What type of bond does RNA polymerase use to bing NTPs together?
Covalent
26
What is released when RNA polymerase binds NTPs together?
Two additional phosphates
27
What direction does transcription occur in?
5' - 3' direction
28
Why does transcription occur in a 5' - 3' direction?
The 5' phosphate is linked to the 3' end of the growing mRNA strand
29
What are the three stages of transcription?
Inititation Elongation Termination
30
What happens in initiation?
RNA polymerase binds to the promoter and causes the unwinding and separating of the DNA strands
31
What happens in elongation?
The RNA polymerase moves along the coding sequence in a 5' - 3' direction
32
What happens in ternination?
The RNA polymerase reaches the terminator and both the enzyme and nascent RNA strand detach and the DNA rewinds
33
Why can a large number of transcripts be produced?
Many RNA polymerase enzymes can transcribe a DNA sequence sequentially
34
In eukaryotes what is necessary to form mature mRNA?
Post transcriptional modification of the RNA sequence
35
In eukaryotes what are the three post transcriptional events that must happen for mature mRNA?
Capping Polyadenylation Splicing
36
What is capping?
The addition of a methyl group to the 5' end of the transcribed RNA
37
What does the methylated cap provide in capping?
Protection against degradation by exonucleases
38
What does capping allow the transcript to do?
Be recognised by the cells translational machinery
39
What is polydenylation?
The addition of a long chain of adenine nucleotides to the 3' end of the transcript
40
What is the long chain of adenine nucleotides also known as?
poly-A-tail
41
What does the poly-A-tail improve?
The stability of the RNA transcript and facilitates its export form the nucleus
42
What is splicing?
The process by which introns are removed
43
In eukaryotic genes what must be removed prior to forming mature mRNA?
Introns
44
What are introns?
Intruding Non-coding sequences
45
What are the coding regions called?
Exons
46
What happens to exons when introns are removed?
They are fused together to form a continuous sequence
47
In splicing are introns or exons being kept?
Exons are being kept
48
What is alternative splicing?
When splicing can also result in the removal of exons
49
What does the selective removal of specific exons result in?
The formation of different polypeptides from a single gene sequence
50
What is transcriptional activity regulated by?
Two groups of proteins
51
What do transcription factors form?
A complex with RNA polymerase at the promoter
52
What do levels of transcriptional factors regulate?
Gene expression
53
Why do transcriptional factor levels regulate gene expression?
As RNA polymerase cannot initiate transcription without them
54
What do regulatory proteins bind to?
DNA sequences
55
Where do regulatory proteins bind to DNA sequences?
Outside the promoter
56
What do regulatory proteins interact with?
The transcription factors
57
What do activator proteins bind to?
Enhancer sites
58
How do activator proteins affect the rate of transcription?
Increase it by mediating complex formation
59
What do repressor proteins bind to?
Silencer sequences
60
How do repressor proteins affect the rate of transcription?
Decrease it by preventing complex formation
61
In gene expression what may be tissue specific?
The presence of certain transcription factors or regulatory proteins
62
How can chemical signals mediate a change in gene expression?
By moderating protein levels
63
What are control elements?
The DNA sequences that regulatory proteins bind to
64
Where are control elements located?
proximal or distal to the promoter
65
What are the two types of control elements?
Distal control elements Proximal control elements
66
What typically binds to distal control elements?
Regulatory proteins
67
What typically binds to proximal control elements?
Transcription factors
68
Why is gene expression a tightly controlled and coordinated process?
As most genes have multiple control elements
69
What can cause changes to gene expression patterns?
Changes in the external or internal environment
70
What can chemical signals within the cell trigger?
Changes in levels of regulatory proteins or transcription factors in response to stimuli
71
What does chemical signals allow in gene expression?
To change in response to change to intracellular and extracellular conditions
72
How can humans change their gene expression patterns in response to environmental changes?
Producing different amounts of melanin depending on light exposure
73
How can hydrangeas change their gene expression patterns in response to environmental changes?
Can change colour depending on the pH of the soil
74
How can himalayan rabbits change their gene expression patterns in response to environmental changes?
By producing a different fur pigment depending on the temperature
75
What is eukaryotic DNA wrapped around?
Histone proteins
76
Why is eukaryotic DNA wrapped around histone proteins?
To form compact nucleosomes
77
What determines how tightly packaged DNA is?
The histone proteins have protruding tails
78
Why do histone tails associate tightly with DNA?
As histones have a positive charge and DNA has a negative charge
79
How does adding an acetyl group to the tail affect the charge?
It neutralises it
80
How does adding an acetyl group to the tail affect transcription?
It increases transcription as it makes DNA less tightly coiled
81
How does adding a methyl group to the tail affect the charge?
It maintains the positive charge
82
How does adding a methyl group to the tail affect transcription?
Reduces it as it makes DNA more coiled
83
What is acetylation?
Adding an acetyl group to the tail
84
What is methylation?
Adding a methyl group to the tail
85
What is condensed heterochromatin?
When DNA is supercoiled and not accessible for transcription
86
What is euchromatin?
When DNA is loosely packed and accessible for transcription
87
Are segments of DNA always supercoiled?
Sometimes but it can change over the life cycle of the cell
88
What can direct methylation of DNA also affect?
Gene expression patterns
89
How does increased methylation of DNA affect gene expression?
Decreases it by preventing the binding of transcription factors
90
What types of genes exhibit more DNA methylation?
Genes that are not transcribed
91
What is epigenetics?
The study of changes in phenotype as a result of variations in gene expression
92
What does epigenetic analysis show about DNA methylation?
The patterns may change over the course of a lifetime
93
What influences DNA methylation patterns?
Heritability but it is not genetically pre-determined and environmental factors
94
Can different cell types in the same organism have different DNA methylation patterns?
Yes

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