A-level biology OCR > Cellular control > Flashcards

Cellular control Flashcards

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1
Q

Define DNA helicase

A

Separates the two strands of DNA by breaking the H bonds

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2
Q

Define RNA polymerase

A

Moves along the template strand causing nucleotides to join with complementary bases

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3
Q

Why do genes need to be able to be turned off?

A

If they were turned on all the time, it would be wasteful

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4
Q

What is induction?

A

Switching a gene on

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5
Q

What is repression?

A

Switching a gene off

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6
Q

What are transcription factors?

A

Proteins that help RNA polymerase attach to the promoter region

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7
Q

Conditions for a gene to be transcribed?

A

RNA polymerase must attach to the DNA of the gene

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8
Q

How does transcription control happen in eukaryotes?

A

Via promoter sequences close to the transcription unit

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9
Q

2 additional major mechanisms of transcription control?

A

1= large scale changes in chromatn structure
2= modifictaion of bases in the DNA sequence

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10
Q

Define chromatin

A

A chain of nucleosomes

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11
Q

Define nucleosomes

A

Strands of DNA wrapped around histones

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12
Q

Histones and DNA during transcription?

A

Histones remain associated with DNA even during transcription

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13
Q

What is euchromatin?

A

A loosely packed form of DNA

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14
Q

Why is
euchromatin accessible to transcrition machinery?

A

It is transcriptionally active

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15
Q

What is heterochromatin?

A

A tighty packed form of DNA

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16
Q

Why is heterochromatin inaccessible to transcription machinery?

A

It is transcriptionally inactive

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17
Q

2 things involved in histone modification?

A

histone acetylation and deacetylation

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18
Q

Why are histone proteins tightly bound to the DNA?

A

Due to the positive charges imparted to them by their basic amino acids

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19
Q

2 things to note about the structure of histone tails

A
  • abundant lysine residues
  • residues carrying a positive charge
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20
Q

Where do histone tails emerge and insert?

A

Emerge= from the histone complex
INsert= INto the minor groove of DNA

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21
Q

Reason DNA tails bind tightly to these histone tails

A

=ionic interactions btwn +ve charge of lysine residues and -ve charges of DNA phosphate groups

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21
Q

3 roles of acetylation?

A
  • negates the +ve charge of the lysine residues on histones
  • heterochromatin changes in2 euchromatin, CAUSING ACTIVATION OF THE GENE
  • regulate gene expression in eukaryotesby regulating acess of transcription enzymes to DNA
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22
Q

How and why are histones made more hydrophobic?
What does this suppress?

A
  • adding methyl groups to histones
    -more ydrophobic=bind more tughtly 2 each other= causes DNA to coil more tightly
  • suppresses the transcription of the affected gene
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23
Q

What is a locus?

A

Fixed position of the gene on a strand of DNA

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24
Each amino acid is coded for by a ____________-
Codon
25
3 words to describe the DNA code?
Degenerate, non-overlapping, universal
26
Define a mutation in a gene?
Spontaneous random change in the genetic material
27
2 moments mutations generally occur?
1=when DNA is copied 2= When a cell divides
28
3 environmental factors that increase mutation rate?
Ionising radiation, UV radiation, Mutagenic chemicals (benzene/phenols)
29
What is a substitution/point mutation?
A nucleotide is substituted for another
30
What is the mutation for sickle cell anemia?
T for an A in haemoglobin
31
Further effects of a change in the base sequence
base sequence->amino acid sequence: primary,secondary,tertiary structure of a protein
32
3 effects of a substitution?
Nonsense, Mis-sense, silent
33
What is a non-sense mutation?
Mutation results in one of the 3 stop codons
34
What is a mis-sense mutation?
Results in a different amino acid sequence being coded for
35
What is a silent mutation?
Although it is a different codon, the same amino acid is coded for
36
What is an insertion mutation?
An extra nucleotide may be added
37
What is a deletion mutation?
A nucleotide is removed
38
What is a frame-shift?
- result of insertion/deletion -causes all firther amino acids to be changed including stop/start codons
39
3 effects of a mutation?
neutral, harmful, beneficial
40
What is a neutral effect?
normal functioning proteins still synthesised, phenotype of organism is unchaged
41
What is a harmful effect?
Proteins not synthesised or are non-functional. Phenotype of organism is negatively impacted
42
What is a beneficial effect?
Protein synthesised with a new and useful characteristic in the phenotype
43
2 examples of harmful mutations?
- protooncogens 2 oncogens by a point mutation = cancer - huntingtons disease = stutter
44
An example of a beneficial mutation?
Speckled moth appearance is recessive, ten industrial revolution
45
What is an operon?
A section of DNA that contains a cluster of genes that are all transcribed together as well as control elements and a regulatory gene
46
Operon more common in prokaryotes or eukaryotes?
prokaryotes
47
3 things the operon consists of?
- structural genes - an operator gene - a promoter region
48
Role of structural genes in operon?
code for the production of enzymes
49
Role of operatpr gene in operon?
Regulates the structural genes
50
Role of a promoter region?
RNA polymerase attaches herre
51
Role of the regulator genes?
code for a repressor protein
52
How is the behaviour of the repressor protein determined?
depends on wether the gene is induced or repressed
53
Define the lac operon
A group of genes in the bacterium that control the metabolism of lactose allowing them to use lactose as an energy source where glucose is scarce
54
3 enzymes involved in the lac operon
lac Z (β-galactosidase), lac Y (lactose permease), lac A (transacetylase)
55
Function of β-galactosidase?
Breaks lactose-> glucose + galactose
56
Function of lactose permease
transports lactose into the cell
57
Function of transacetylase
modifies lactose or its by-products
58
4 steps to the functioning of the lac operon in the abscence of lactose
1= repressor protein binds to the operator region 2= RNA polymerase is blocked from the promoter region 3= RNA polymerase can't transcribe the structural genes 4= the enzymes for lactose metabolism aren't produced
59
4 steps to the functioning of the lac operon in the prescence of lactose
1= lactose binds to the repressor protein 2= repressor protein changes shape and is released from the operator region 3= RNA polymerase can bind to the promoter region and initiate transcription 4= RNA polymerasr transcribes the structural genes leading to the production of enzymes neccessary for lactose metabolism
60
When the transcriptiona level of gene control happen?
During mRNA production
61
When the post-transcriptional level of gene control happen?
after mRNA production, after protein production
62
Define introns
sections of DNA that do not code for proteins
63
Define exons
Setions of DNA that do code for proteins
64
premRNA still contains...
'junk DNA' called introns
65
Define splicing
when introns are removed and functional exons are joined together in the pre-mRNA of eukaryotic cells
66
Why do we need splicing?
to remove introns
67
Enzyme that catalyses splicing?
spliceosome
68
effect of shape of intron by spliceosome?
Causes the intron to form a loop shape
69
The introns are _______ then and the exons are then _________ together
excised, spliced
70
What happens in alternative splicing?
more than one mRNA can be made from the same gene
71
Alternative splicing increases __________
biodiversity
72
What is exon skipping?
cauuses cells to skip over faulty/misaligned sections of the genetic code that result from genetic mutation
73
Why is exon skipping useful?
restores the reading frame within the gene
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