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A-Level Biology > 19 Genetics of Living Systems > Flashcards

19 Genetics of Living Systems Flashcards

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1
Q

What is a mutation?

A

a change in sequence of bases in DNA.

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2
Q

What a change in sequence be caused by? (3 ways)

A

Substitution, deletion and insertion

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3
Q

What is substitution?

A

one or more bases are swapped for another base.

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4
Q

What is deletion?

A

one or more bases are removed.

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5
Q

What is insertion?

A

one or more bases are added.

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6
Q

What is a frameshift mutation?

A
  • When the insertion or deletion of a nucleotide shifts the reading frame of the sequence of bases.
  • This will change every successive codon from the point of mutation.
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7
Q

Why isn’t there a frameshift mutation when bases are added in a multiple of three?

A

Multiples of three correspond to full codons and therefore the reading frame will not be changed, but the protein formed will still be affected as a new amino acid is added.

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8
Q

Give 3 reasons why a mutation may have a neutral effect.

A

1) The mutation produces a triplet that codes for a chemically similar amino acid so that it functions like the original amino acid.
2) The mutation produces a base triplet that still codes for the same amino acids.
3) The mutation produces a base triplet that codes for a amino acid that’s not involved with the protein’s function.

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9
Q

Why may mutations be beneficial? (Give example)

A
  • A protein is synthesised that results in a new useful characteristic in the phenotype.
  • E.g Bacterial enzymes have mutations that enable them to work on a wider range of antibiotics. This is beneficial because antibiotic resistance can help them survive.
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10
Q

Why may mutations be harmful? (Give example)

A
  • The phenotype of an organism is affected in a negative way because proteins are no longer synthesised or proteins synthesised are non functional.
  • E.g cystic fibrosis is caused by deletion of three bases, and this leads to excess mucus production affecting the lungs of CF sufferers.
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11
Q

What is a mutagen?

A

A mutagen is a chemical, physical or biological agent which increases rate of mutation.

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12
Q

Give some causes of mutations.

A

1) Spontaneous loss of a purine or pyrimidine base

2) Free radicals affecting the structures of nucleotides and disrupt base pairing.

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13
Q

How are changes in the chromosomes brought about? (4 ways)

A

Deletion, Duplication, Translocation and Inversion

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14
Q

What occurs in deletion? (Chromosome)

A

A section of chromosome breaks off and is lost within the cell.

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15
Q

What occurs in duplication? (Chromosome)

A

Sections get duplicated on a chromosome

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16
Q

What occurs in translocation? (Chromosome)

A

A section of one chromosome breaks off and joins another non-homologous chromosome

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17
Q

What occurs in inversion? (Chromosome)

A

A section of chromosome breaks off, is reversed, and then joins back onto the chromosome.

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18
Q

At which levels can gene regulation operate?

A
  • Transcriptional: Genes can be turned on or off
  • Post-transcriptional: modifies mRNA
  • Translational: Translation can be stopped or started (whether protein is synthesised or not)
  • Post-translational: Proteins can be modified after synthesis which changes their function.
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19
Q

What is heterochromatin?

A

Heterochromatin is tightly wound DNA causing chromosomes to be visible during cell division.

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20
Q

What is euchromatin?

A

Euchromatin is loosely wound DNA present during interphase.

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21
Q

Why is the transcription of genes not possible when DNA is tightly wound?

A

RNA polymerase cannot access the genes.

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22
Q

When does protein synthesis occur?

A

Protein synthesis occurs during interphase between cell divisions.

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23
Q

Why does DNA coil around histones?

A

histones are positively charged and DNA is negatively charged

24
Q

How can histones be modified so that DNA coils less tightly?

A
  • The addition of acetyl groups (acetylation) or phosphate groups (phosphorylation) reduces the positive charge on the histones
  • this causes DNA to coil less tightly.
25
Q

How can histones be modified so that DNA coils more tightly?

A

The addition of methyl groups makes the histones more hydrophobic so they bind more tightly to each other causing DNA to coil more tightly and preventing the transcription of genes.

26
Q

What is epigenetics?

A

changes in DNA that alter the expression of genes without changing base sequence of DNA itself, these changes are caused by environmental factors and are heritable

  • chemical tags are added to DNA or histones
27
Q

What is an operon?

A

a group of genes that are under the control of the same regulatory mechanism and are expressed at the same time.

28
Q

What is the lac operon?

A

The lac operon is a group of three genes: lacZ, lacY, and lacA, involved in the metabolism of lactose.

29
Q

What type of genes is the lac operon?

A

They are structural genes as they code for 3 enzymes and are transcribed onto a single long molecule of mRNA.

30
Q

What does the regulatory gene do?

A
  • located near the operon
  • codes for proteins involved in DNA regulation
  • example : Lac I codes for repressor protein
  • makes repressor protein which control which genes witch on and off
31
Q

What does the repressor gene do?

A

The repressor gene prevents the transcription of structural genes in the absence of lactose.

32
Q

What does the binding of the repressor protein to the operator prevent ?

A

prevents RNA polymerase binding to DNA and beginning transcription. This is called DOWN REGULATION.

33
Q

What is the promoter?

A

The section of DNA that RNA polymerase binds to

34
Q

When lactose is present what occurs?

A
  • When lactose is present, it binds to the repressor protein causing it to change shape so it can no longer bind to the operator.
  • As a result RNA polymerase can bind it to the promoter, the three structural genes are transcribed, and the enzymes are synthesised.
35
Q

How is the rate of transcription increased?

A

The binding of cAMP receptor protein (CRP)

36
Q

The transport of which molecule decreases levels of cAMP?

A

The transport of glucose decreases levels of cAMP, reducing the transcription of the genes responsible for the metabolism of lactose.

37
Q

What is the product of transcription?

A

A precursor molecule, pre-mRNA

38
Q

What is pre-mRNA modified into?

A

pre-mRNA is modified into mature mRNA before it can bind to a ribosome

39
Q

How is mRNA processed?

A
  • A cap (modified nucleotide) is added to the 5’ end.

- A tail (long chain of adenine nucleotide) is added to the 3’ end.

40
Q

What are the benefits of adding a cap and tail to mRNA?

A
  • These help to stabilise mRNA and delay degradation in the cytoplasm.
  • The cap also aids binding of mRNA to ribosomes.
41
Q

What is splicing?

A

The introns (non-coding DNA) are removed and the exons (coding DNA) are joined together.

42
Q

How is mRNA edited?

A
  • The nucleotide sequence of some mRNA molecules can also be changed through base addition, deletion or substitution.
43
Q

Which mechanisms regulate the process of protein synthesis? (TRANSLATIONAL CONTROL)

A

To down regulate translation (don’t want protein to be synthesised ) -

  • Degradation of mRNA: The more resistant the molecule, the longer it will last in the cytoplasm and so a greater quantity of protein synthesised.
  • Binding of inhibitory proteins to mRNA prevents it binding to ribosomes and the synthesis of proteins.

To activate translation (want protein to be synthesised) -
- Activation of initiation factors which aid the binding of mRNA to ribosomes

44
Q

What are protein kinases?

A
  • Protein kinases are enzymes that catalyse phosphorylation
45
Q

What are protein kinases often activated by?

A

Protein kinases are often activated by the secondary messenger cAMP

46
Q

How does post-translational control modify the proteins that have been synthesised?

A
  • Addition of non-protein groups such as carbohydrate chains, lipids, or phosphates.
  • Modifying amino acids and the formation of bonds such as disulfide bridges.
  • Folding or shortening of proteins.
  • Modification by cAMP
47
Q

What is morphogenesis?

A

The regulation of the pattern of anatomical development

48
Q

What are homeobox genes?

A

group of genes which all contain a homeobox

49
Q

What is a homeobox?

A
  • they are regulatory genes
  • contains 180 bp that codes for homeodomain
  • binds to DNA and initiates transcription, switches genes on and off
  • control of body plan /development
50
Q

What is this part of the protein called and what does it do?

A

Homeodomain

- Homeodomain binds to DNA and switches other genes on or off .

51
Q

What are hox genes?

A
  • example of a group of homeobox genes that are only present in animals
  • humans have 39 hox genes
52
Q

What are hox genes responsible for?

A

Hox genes are responsible for the correct positioning of body parts.

53
Q

In animals how are Hox genes found?

A

In animals, the Hox genes are found in gene clusters-mammals have four clusters on different chromosomes.

54
Q

What is a body plan?

A

general structure of an organism.

55
Q

What is apoptosis?

A

programmed cell death

56
Q

How does apoptosis shape different body parts?

A
  • Apoptosis removes unwanted cells and tissues.
  • Cells undergoing apoptosis can also release chemical signals which stimulate mitosis and cell profileration leading to the remodelling of tissues.
57
Q

What factors affect the expression of regulatory genes?

A

The expression of regulatory genes can be influenced by the environment, both internal and external.

A-Level Biology (41 decks)

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