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Year 1 - Semester 1 > Week 3 - Genetics > Flashcards

Week 3 - Genetics Flashcards

1
Q

What are non-sex chromosomes called

A

Autosomes

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2
Q

What two things is DNA associated with?

A

Histones - small, positively charged proteins which have two of each H2A, H2B, H3 and H4 (octamer) - highly conserved in evolution

Chromatin - Non-histome chromosomal protein

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3
Q

Explain how chromosome structure is dynamic

A

More condensed during mitosis than other phases of the cell cycle - less condense to allow gene expression, repair and replication

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4
Q

How can chromatin be made more accessible?

A

Histone tails can be reversibly chemically modified

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5
Q

What is a nucleosome?

A

One histone core and the DNA wrapped around it

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6
Q

What is the centromere?

A

Highly repetitive DNA sequence which can stretch over megabases (10^6) - constriction point of a pair of chromatids - bound by large protein complexes called kinetochores

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7
Q

What are telomeres?

A

Long, repetitive DNA sequence (TTAGGG) which forms a loop. Protects the end of the chromosome from natural cellular exonucleases, maintaining chromosome integrity

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8
Q

What is a nucleotide?

A

A 5-carbon sugar (2-deoxyribose), phosphate and a base (nitrogen containing ring)

T as in THREE

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9
Q

What is a nucleoside?

A

Just a base and a sugar

Adenosine, guanosine

Cytidine, thymidine

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10
Q

What are pyrimidines?

A

Single ring

cYtosine and thYmine

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11
Q

What are purines?

A

Double ring

adenine and guanine - neither have a Y

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12
Q

What is thymine replaced with in RNA?

A

Uracil

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13
Q

How many hydrogen bonds between cytosine and guanine?

A

3

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14
Q

How many hydrogen bonds between thymine and adenine?

A

2

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15
Q

Why are DNA strands called antiparallel?

A

They run in opposite directions

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16
Q

What is the 5’ end?

A

The start of the chain, has a free 5’ phosphate

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17
Q

What is the 3’ end?

A

The end of the chain, has a free 3’ OH

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18
Q

Which end does DNA polymerase add nucleotides to?

A

3’ 3 is lower than 5, needs to be added to

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19
Q

Which stand is synthesized continuously?

A

Leading strand

Lagging strand is synthesized in sections called okazaki fragments - later fused by DNA ligase

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20
Q

What is DNA polymerase known as?

A

A primase - as it makes a RNA primer first

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21
Q

What helps unwind the double helix?

A

Helicase

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22
Q

How many primers needed for each strand?

A

Leading requires one

Lagging has continuous requirement - later removed by nucleases

23
Q

How often does DNA polymerase make a mistake?

A

One in 10^7 bases

Overall accuracy is 10^9 from repair

24
Q

What can UV light cause?

A

Thymine dimers

25
Q

Which is DNA replication called semiconservative?

A

Half of the parent strand is kept

26
Q

What DNA sequences are likely to be evolutionarily constrained?

A

Sequences which are functionally important

27
Q

Describe the differences between DNA and RNA

A 
DNA is long - RNA is short
Double stranded - single stranded
Simple double helix structure - complex 3D like a protein
Chemically stable - less stable
Deoxyribose - ribose
Thymine - uracil
28
Q

What is a gene?

A

A region of DNA which controls a discrete hereditary characteristic, usually corresponding to a single protein or RNA

29
Q

How many cells does an adult human have

A

~10^13

30
Q

What is a promoter?

A

Sequences immediately before 5’ end of gene that interact with RNA polymerase

31
Q

What is an enhancer?

A

Increases transcription from a nearby gene - can operate over considerable distances

32
Q

What are transcription factors?

A

Proteins which bind to specific DNA sequences within a promoter or enhancer to increase or decrease gene expression

33
Q

How can expression of a single gene be controlled?

A

Alternative promoters

Alternative splicing

Alternative polyadenylation

34
Q

What is the difference between exons and introns

A

EXons are EXpressed - Code for proteins

Introns are intervening sequences

35
Q

What is polyadenylation?

A

A polyA tail is a string of adenylate residues added to the 3’ end of an mRNA - not on tRNA or rRNA

36
Q

What are the untranslated regions?

A

5’ upstream of translated region - may affect translational control

3’ downstream of translated region - can determine stability of the mRNA

37
Q

Explain PCR

A

Used for genotyping to detect mutations

Heated to 95 to cause 2 strands to separate
Cooled to 55 to allow primers to anneal
Heated to 72 to synthesise new DNA strands using thermophilic DNA polymerase

38
Q

Genotype and phenotype difference

A

Genotype is an individual’s genome

Phenotype is their set of characteristics

39
Q

Why is there redundancy in codons?

A

64 codons (4x4x4) and only 20 amino acids plus 3 stop codons

40
Q

Describe a ribosome

A

Made of rRNA and proteins

Had large and small subunits

A - aminoacyl tRNA site

P - peptidyl tRNA site

E - Exit site

mRNA binding site

41
Q

Describe the cycle of translation

A

Recognises start codon (methionine) which is usually cleaved away

mRNA codon determines which tRNA binds

New peptide bond formed between amino acids in the P and A sites

Large subunit translocates and shifts tRNAs into the E and P sites

Small unit translocates and the ribosome is reset with vacant A site

42
Q

Describe crossing over

A

When homologous chromosomes line up, genetic information can cross over at points called chiasmata between non-sister chromatids

43
Q

Describe independent assortment

A

Maternal and paternal chromosomes are shuffled and dealt randomly at meiosis 1

2^N different gametes

In humans - 2^23 = 8.4 million genetically distinct gametes

44
Q

Aneuploidy vs polyploidy

A

Aneuploidy is more or less of one chromosome

Polyploidy is more than 2 sets of chromosomes

45
Q

What’s the law of segregation

A

2 alleles for each trait segregate during gamete formation and then unite at random during fertilisation

46
Q

What is the law of independent assortment

A

Alleles of two different genes get sorted into gametes independently - the allele a gamete receives for one gene does not influence the allele received for another

Genes closer together on a chromosome are more likely to be inherited as a unit

47
Q

What are some endogenous sources of mutation

A

Spontaneous damage, errors in chromosome segregation, recombination, DNA replication, DNA repair

48
Q

What does deamination lead to?

A

C –> T transition

49
Q

What does xeroderma pigmentosum lead to?

A

Unable to repair thymine dimers - extensive skin cancer

50
Q

How can genetic variation cause disease?

A

Loss of function - becomes useless

Gain of function - can be harmful

Too much gene product

Too little gene product

51
Q

Name types of mutations

A

Point - aka substitution - likely resultant protein is still functional - can be synonymous (where the protein is the same) or non synonymous (where it’s different)

non synonymous can be:

  • nonsense - codes for a stop codon - truncated protein
  • missense - creates an amino acid with different chemical properties
  • splice site - changes order of Exons and introns

Deletion - frameshift - less likely to make a functional protein

Insertions - frameshift - less likely to make a functional protein

52
Q

Types of chromosomal mutations

A

Non-allelic homologous recombination where one sequence is deleted and another is duplicated

53
Q

Give an example of how modifying the environment can have an influence in outcome when there is a mutation

A

PKU metabolic disease
Mutation in gene encoding phenylalanine hydroxylase
Cannot convert phenylalanine to tyrosine which results in toxin buildup leading to intellectual disability
Can be diagnosed with a heel prick test (Guthrie test)
Infant can be put on a low phenylalanine diet

54
Q

How can histone tails be genetically modified?

A

Methylation
Acetylation
Phosphorylation

Year 1 - Semester 1 (9 decks)

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