Biology AS > Genetics > Flashcards

Genetics Flashcards

(53 cards)

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1
Q

Define transcription factor

A

Proteins that bind to specific DNA sequences and control the rate of transcription.

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2
Q

What is mutation

A

A gene mutation is a change in the DNA base sequence.

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3
Q

What are the three types of gene mutations

A

Substitution - One base is replaced by another.
Deletion - One base is removed from the sequence.
Insertion - One base is added into the sequence.

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4
Q

Define epigenetics.

A

changes in gene expression that do not involve changes to the DNA base sequence.

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5
Q

What is DNA methylation? And effect

A

This involves adding methyl groups to histones, increasing hydrophobic interactions and tightening the coiling of DNA, which reduces transcription

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6
Q

What is histone modification?

A

Chemical modification of histone proteins (e.g. acetylation).

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7
Q

Effect of histone acetylation.

A

Increases gene expression by reducing attraction between histones and DNA, making DNA more accessible.

promote transcription

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8
Q

Define alternative splicing.

A

Different combinations of exons are joined to produce different mRNA from the same gene.

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9
Q

Advantage of alternative splicing.

A

Allows one gene to code for multiple proteins, increasing protein diversity.

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10
Q

Define mutagen.

A

A substance or factor that increases the rate of mutation.eg Ionising radiation and chemicals (e.g. benzene).

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11
Q

What is a frameshift mutation?

A

A mutation that alters the reading frame of the genetic code

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12
Q

Why do insertions and deletions often cause frameshifts?

A

Because bases are not added or removed in multiples of three

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13
Q

What is a silent mutation?

A

A base change that does not alter the amino acid sequence.

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14
Q

What is a missense mutation?

A

A mutation that results in a different amino acid being coded.

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15
Q

What is a nonsense mutation?

A

A mutation that produces a stop codon, resulting in a shortened polypeptide.

produce incomplete proteins that are usually non-functional.

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16
Q

Regulatory gene

A

These encode proteins that regulate the expression of the structural genes.

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17
Q

promoter region

A

site where RNA polymerase binds to initiate transcription.

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18
Q

operator region

A

This is a sequence where regulatory proteins (like repressor proteins) can bind.

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19
Q

Structural gene(s)

A

These genes code for proteins, typically enzymes.

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20
Q

What does the lac operon control

A

The production of enzymes needed to break down lactose.

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21
Q

How the lac operon functions when lactose is absent

A

The repressor protein binds to the operator region.
RNA polymerase is blocked from the promoter region.
RNA polymerase can’t transcribe the structural genes.
The enzymes for lactose metabolism aren’t produced.

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22
Q

How the lac operon functions when lactose is present

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A

Lactose binds to the repressor protein.
The repressor protein changes shape and is released from the operator region.
RNA polymerase can bind to the promoter region and initiate transcription.
RNA polymerase transcribes the structural genes, leading to the production of enzymes necessary for lactose metabolism.

23
Q

Importance of lac operas

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A

designed to conserve energy by producing lactose-metabolising enzymes only when lactose is present.

24
Q

When only lactose is present:
cAMP

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A

cAMP levels increase, and cAMP binds to the cAMP receptor protein (CRP).
The CRP-cAMP complex increases the rate of the transcription of the lac operon.
Lactose metabolism is optimised

25
When both glucose and lactose are present: cAMP
Glucose reduces cAMP levels. The CRP-cAMP complex cannot form. The lac operon's transcription is downregulated (rate decreases ). Lactose metabolism enzymes are not produced. Glucose presence, therefore, suppresses lactose metabolism in favour of the more efficient energy source.
26
Why is the lac operon described as inducible
It is switched on only when lactose is present.
27
What are introns
non-coding regions of DNA
28
29
How is pre -, mRNA modified
-Addition of a 5’ cap - This stabilises the mRNA, delays its degradation, and assists in ribosome binding. -Addition of a 3’ poly-A tail - This stabilises the mRNA and delays its degradation. -Splicing - Introns are removed and exons are joined together, providing the instructions for the protein sequence. In nuclues
30
Where does splicing occur?
A: In the nucleus.
31
Why must introns be removed?
They are non-coding and would disrupt translation.d
32
What is Translational control
The rate at which translation occurs can be finely regulated to control the levels of protein produced.
33
Factors that affect the rate of translation
Factors that affect the rate of translation mRNA degradation rates: mRNA that degrades slowly is more stable and lasts longer. This can increase translation and protein synthesis. Inhibitory proteins: These can bind to mRNA, preventing it from attaching to ribosomes. This decreases translation and protein synthesis. Initiation factors: Activated initiation factors help mRNA bind to ribosomes. This initiates translation and increases protein synthesis. P
34
What are Initiation factors
Activated initiation factors help mRNA bind to ribosomes. This initiates translation and increases protein synthesis.
35
What areInhibitory proteins:h
bind to mRNA, preventing it from attaching to ribosomes. This decreases translation and protein synthesis.
36
What are mRNA degradation rates
mRNA that degrades slowly is more stable and lasts longer. This can increase translation and protein synthesis.
37
Eg of Post-translational modification (can influence their function.)
The addition of carbohydrates, lipids, or phosphate groups. The formation of disulfide bridges between amino acids. The shortening of peptide chains. increase the diversity of proteins
38
Define body plan
The basic structured arrangement of an organism's parts, which are determined by genetic and developmental factors.
39
Define Homeobox genes
A group of regulatory genes with a conserved DNA sequence that guides the development of body plans
40
Define Homeobox sequence
A highly conserved DNA sequence ( of about 180 base pairs , 60 amino acid long ) found within homeobox genes that is crucial for the development of an organism's body plan.
41
Define Hox gene
A subset of homeobox genes in animals, containing homeobox sequences essential for the correct positioning of body parts.
42
how Hox genes control development:
Hox genes contain homeobox sequences, which code for a homeodomain • The homeodomain forms part of a protein that binds to specific DNA sequences. • This protein acts as a transcription factor. • It switches other genes on or off, controlling gene expression. • This regulates the transcription of proteins needed for development, determining the body plan and position of structures.
43
Why homeobox genes are so conserved
A mutation would have large effects by altering the organism's body plan. Many other genes would also be affected by a mutation in a homeobox gene. Mutations are likely to be lethal and selected against.
44
Why are fruit flies used in studies on the activity of genes that control body plan.
- low cost. - rapid reproduction rate. - have a simple body plan. - Their mutations can be studied with a low-powered microscope.
45
What two processes shape body morphology during developme
Mitosis and apoptosis, along with cell differentiation.
46
How do mitosis and apoptosis work together during development
Mitosis adds new cells, while apoptosis removes unnecessary cells, shaping tissues and organs.
47
Give an example of apoptosis and mitosis shaping body structure.
Mitosis increases cell number in developing fingers, while apoptosis removes connective tissue between them, removing webbing.
48
What processes do Hox genes control?
Rate and location of cell division (mitosis) • Programmed cell death (apoptosis) during development.
49
Why is regulation of apoptosis and mitosis important?
To maintain a balance between cell removal and cell renewal.
50
Give examples of internal stimuli that affect developmental (regulatory )genes.
• Stress • Drugs • Hormones
51
What problem can internal stimuli cause?
DNA damage.
52
How do regulatory genes respond to DNA damag
They stop the cell cycle and trigger apoptosis. prevent damaged DNA being replicated into new cell
53
Give examples of external stimuli affecting developmental genes.
Temperature changes • Light intensity
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