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BIOL1010/1011 > Genetics: Lecture 6 > Flashcards

Genetics: Lecture 6 Flashcards

Regulation of Gene Expression and Gene Mutations

1
Q

Cuatro Ojos genes?

A

The Cuatro Ojos “Four Eyes” fish has two different gene expressions in its eyes. The top half and bottom half both express different genes.

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2
Q

Advantage of Cuatro Ojos gene expression?

A

ADVANTAGE OF TWO GENES EXPRESSED:

  • Can see predators from above
  • Can see prey from below
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3
Q

Structure of a prokaryotic gene?

A
  • DNA
  • Promoter
  • Operator
  • Coding Sequence
  • Terminator
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4
Q

What does the operator do?

A

The operator can turn on and off. It is induced by an inducer.

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5
Q

What does the coding sequence produce?

A

The coding sequence produces structural genes.

  • They can have several genes back to back
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6
Q

Prokaryotic gene - protein

A

The coding sequence undergoes transcription and translation, creating a protein at the end.

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7
Q

Prokaryotes vs. Eukaryotes: Structure of genome?

A

Prokaryotes: Single, generally circular genome sometimes companied by smaller pieces of accessory DNA, like plasmids.

Eukaryotes: Genome found in chromosomes; nucleosome structure limits DNA accessibility.

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8
Q

Prokaryotes vs. Eukaryotes: Size of genome?

A

Prokaryotes: Relatively small (few thousand to 1 million base pairs)

Eukaryotes: Relatively large (a few million to 3 billion base pairs or more)

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9
Q

Prokaryotes vs Eukaryotes: Location of gene transcription and translation?

A

Prokaryotes: Coupled; no nucleoid envelope barrier because of prokaryotic cell structure.

Eukaryotes: Nuclear transcription ad cytoplasmic translation

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10
Q

Prokaryotes vs. Eukaryotes: Gene clustering?

A

Prokaryotes: Operons where genes with similar function are grouped.

Eukaryotes: Operons generally not found in eukaryotes; each gene has its own promoter element and enhancer element(s).

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11
Q

Coupled transcription/translation?

A

Means that both can occur at the same time.

  • While mRNA is formed, the ribosome can latch on and begin translation.
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12
Q

Prokaryotic vs. Eukaryotic cells?

A

Prokaryotic: everything is all mixed together

Eukaryotic: distinct areas like nucleus and other membrane-enclosed organelles.

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13
Q

Polysome/Poly Ribosome?

A

Provided that there are good conditions, an incomplete mRNA that is done with one ribosome can have another snap onto it and begin synthesizing another new protein.

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14
Q

Structure of an Operon?

A
  • Promotor
  • Operator
  • Gene/DNA sequence
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15
Q

Transcription and translation of an operon?

A

Moves downstream (5’ - 3’), transcribing genes A, B and C.

  • Polygenic mRNA is formed, meaning there are multiple genes synthesized back-to-back.
  • Translation occurs the same, other than there are three polypeptides formed (or as many as there are genes on the operon)
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16
Q

Where is lactose?

A

Lactose can be found in the E. coli membrane.

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17
Q

Lactose composition?

A

Lactose is a disaccharide made up of glucose and galactose, which are joined by a beta glycosidic bond.

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18
Q

What does glucose do for cells?

A

Glucose is an energy source for cells.

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19
Q

Lac Operon?

A

Lactose is not needed so the lactose will turn on the set of genes (operon) that is needed to digest lactose.

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20
Q

What is on the Lac operon?

A

On the lac operon there is LacY, which produces permeate proteins, which, makes the cell permeable to lactose allowing it in when it is present.

There is also LacZ, a gene that produces beta galactosidase which breaks beta glycosidic bonds and allows the cell to use glucose from lactose as an energy source.

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21
Q

Induction of Beta - Galactosidae Synthesis by Lactose in E. coli?

A

There is originally no lactose

When lactose is added to grow medium, induction occurs.

After 10 minutes, around 6% of all protein made by cell is made by lactose - metabolizing enzyme.

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22
Q

The lactose operon components?

A
  • Promotors
  • Operator
  • RNA polymerase
  • Structural genes
  • Regulatory gene
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23
Q

Lac Structural Genes?

A

The structural genes are enzymes that digest things.

Beta - Galactosidase
Permease
Transacetylase

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24
Q

Lac Regulatory Gene?

A

Regulatory genes regulate rhetorical structural genes.

The lac regulatory gene is laci

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25
Q

Blocks Transcription of the Operon?

A

Binding of the Lactose repressor protein to the operator blocks transcription of the operon

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26
Q

Lac Active Repressor?

A

When there is no lactose, the repressor is active and it binds to the operator.

  • You’re not making the genes necessary to digest lactose if there is no lactose around.
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27
Q

Lac I mRNA

A

Lac I is always making mRNA, ensuring that protein can always be made and that protein is going to be the repressor.

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28
Q

Active Repressor effect?

A

When the active repressor attaches to the operator, it is unable to work, not allowing the RNA polymerase to go through. This results in no RNA being made.

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29
Q

Regulatory genes code for ___?

A

Regulatory genes code for regulatory proteins.

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30
Q

What are regulatory proteins?

A

Undergo a conformational change (shape change) upon binding a small molecule (ligand) that decreases or increases the protein’s affinity (binding) for DNA.

31
Q

Example of Regulatory proteins?

A

The LacI repressor protein (a regulatory protein) is inactivated when it binds allolactose (a ligand)

  • Turing on the ligand inactivates the repressor, thereby turning on the gene.
32
Q

Regulatory proteins are examples of _______?

A

Regulatory proteins are examples of allosteric proteins because they have two sites: a regulatory site and an active site.

33
Q

Allosteric?

A

Allostery = allos “other” and stereos “solid (object)”

  • Reference to the fact that the regulatory site of an allosteric protein is physically distinct from its active site.
34
Q

Inactive repressor?

A

An inactive repressor has something bound to the bottom of it, meaning it cannot bind to DNA. This is a simple change but renders the repressor useless!

35
Q

Induction of the Lactose Operon?

A

Lactose is present, repressor is inactive and the operon is on.

  • The RNA polymerase runs along the operon, changing the DNA into an RNA molecule. Multiple peptides (proteins) are formed.
36
Q

Example of Induction of Enzyme Synthesis?

A

Lactose (Lac Operon)

37
Q

Example of Repression of Enzyme Synthesis?

A

Tryptophan (Tryp Operon)

38
Q

Tryp Operon?

A

Goal is to synthesize tryptophan from other molecules, precursor molecules.

39
Q

What happens if there is already tryptophan in the environment?

A

If there is tryptophan in the environment, more doesn’t need to be made by the operon.

  • Therefore, we need to repress it!
40
Q

What is tryptophan?

A

Tryptophan is an amino acid

41
Q

Regulatory Gene?

A

The regulatory gene moves upstream, making it constitutively active. This means it is not turned off and always being made.

42
Q

What happens when there is no tryptophan?

A

At the point when there’s no tryptophan around, the repressor is not binding the operator.

43
Q

Difference between LAC and TRYP?

A

Tryptophan is the ligand for the tryptophan operon, meaning it regulates the genes necessary to make tryptophan itself.

44
Q

What happens when enough tryptophan is present?

A

If there is enough tryptophan present, the tryptophan will activate the repressor.

45
Q

What is the tryptophan operon an example of?

A

The repression of the tryptophan operon by the amino acid tryptophan is a negative feedback loop.

  • This means that the system shuts itself down.
  • What you are producing regulates itself.
46
Q

What can we call Tryptophan?

A

We can refer to tryptophan as a co-repressor or a ligand. It is both!

47
Q

What is a mutation?

A

A mutation is a permanent change in the hereditary material (DNA).

48
Q

What is chromosomal translocation?

A

Chromosomal translocation can occur with trisomy 21 where part of the chromosome relocated to chromosome 14.

  • They have severe consequences, where one can survive but will not be 100% healthy.
49
Q

What is the transposition of genes?

A

This involves “junk” DNA which is ancient, dormant genes.

  • They get turned on and they will cut out other DNA and move it around
50
Q

What are point mutations?

A

Mutations that occur at specific points.

51
Q

What are mutagens?

A

Mutagens are physical and chemical agents that promote mutations in genes.

52
Q

Types of mutagens?

A
  • Ionizing radiation
  • Ultraviolet radiation
  • Chemical mutagens
53
Q

Ionizing radiation?

A

Gamma rays, beta rays, alpha rays.

  • lead to double stranded breaks where both strands of DNA are broken
54
Q

Ultraviolet Radiation?

A

Sun rays

55
Q

Chemical Mutagens?

A

Specific chemicals creating mutations.

56
Q

Physical Mutagens?

A

Radiation

57
Q

Chemical Mutagens?

A

Chemicals

58
Q

Example of Ultraviolet Radiation?

A

Thymidine Dimers

  • When exposed to UV radiation, every single part of the sequence where you see two T’s in a row will bond to one another instead of having two T-A bonds.
  • This forms a kink and shortens the distance between two rungs (less than 0.34nm)
  • DNA polymerase will not recognize these kinks and it will fall off when it gets here, resulting in no replication.
59
Q

DNA Repair Enzymes?

A

Correct Damaged DNA

60
Q

Nuclease?

A

The job of nuclease is to find timers and remove the impacted DNA.

61
Q

DNA Polymerase?

A

Fills in the missing DNA

62
Q

DNA Ligase?

A

Mends the backbone of DNA, finishing the job and making the strand good as new.

63
Q

Chemical mutagen forms?

A
  1. Chemicals that can be incorporated into DNA; they look similar to DNA nucleotides but promote incorrect base pairing.
  2. Chemicals that add or remove groups from nucleotide bases causing incorrect base pairing.

➢Result: a Base-Pair Substitution (or point mutation) is introduced during the replication of DNA.

64
Q

Example of a Nucleotide Analog?

A

5-Bromouracil: very similar to both T and C and can act as either if someone is exposed to it.

65
Q

Silent mutation?

A

A silent mutation is a point mutation that results in the same amino acid/polypeptide being formed.

  • Will oftentimes result from a mutation in the third base
66
Q

Missense mutation?

A

A missense mutation will result in a different amino acid being synthesized.

  • not always bad
  • depends on the differences in category of the amino acids and the place where the change occurs in the amino acid
67
Q

Example of missense?

A

A missense mutation causes sickle cell anemia.

  • very painful disease caused by one single change in the nucleotide sequence
68
Q

Nonsense mutation?

A

A point mutation resulting in there being a stop codon earlier than expected.

69
Q

Frameshift (immediate nonsense)?

A

An insertion or deletion of 1 nucleotide pair that results in a stop codon being formed earlier on.

70
Q

Frameshift (extensive missense)?

A

One nucleotide pair insertion or deletion that sets of a chain reaction of messed up/new amino acid sequence that continues until a stop codon is present.

71
Q

3 nucleotide pair insertion/deletion?

A

An amino acid will be missing from the polypeptide but there won’t be any frameshift.

72
Q

p53 protein?

A

Protects against mutagens caused by chemicals/UV light.

73
Q

What does p53 do?

A

It looks for mismatched DNA during G1 and repairs those issues that it found.

  • prevents S phase from occurring until the issues are fixed.
  • If there are too many errors it will trigger self-destruction
  • cells without p53 would just grow and mutate and continue to do that.
74
Q

Explain whether a cancer causing
mutation in a tumor-suppressor gene, such as p53, is more likely to be a recessive or a dominant mutation?

A

It would be recessive, as the chance of having two parents that are non-functional for this is extremely low. It would be very rare to see it.

BIOL1010/1011 (22 decks)

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