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Dna + Meiosis + Mutations Flashcards

1
Q

DNA in prokaryotes

A
  • circular, double stranded dna
  • not surrounded by a nuclear membrane
  • free in the cytoplasm
  • not associated with proteins
  • shorter
  • doesn’t have introns
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2
Q

Dna in eukaryotes

A
  • long, linear dna
  • dna enclosed in a nucleus
  • associated with proteins (histones)
  • has introns
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3
Q

Mitochondrial + chloroplast dna

A

Similar to dna in prokaryotes (short, circular, no proteins). MtDNA contained in matrix and cpDNA contained in stroma

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4
Q

Genome

A

All the genetic material of an organism

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5
Q

Homologous chromosomes

A

Pairs of chromosomes with genes for same features at same loci

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6
Q

Diploid

A

Containing 2 complete sets of chromosomes, one from each parent

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7
Q

Gene

A

Base sequence of dna that codes for the amino acid sequence of a polypeptide (or a functional RNA

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8
Q

Allele

A

A different version of a gene

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9
Q

A codon

A

3 bases that encodes for a specific amino acid

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10
Q

Degenerate code

A

Multiple codons can code for the same amino acid during protein synthesis

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11
Q

Non-overlapping code

A

Each nucleotide is part of only one codon, each base is only read once, adjacent codons don’t overlap (same letter isn’t used for 2 diff codons)

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12
Q

Universal code

A

The code is the same in almost all organisms, each triplet codes for the same a.a in all organisms

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13
Q

Introns

A

Non coding parts of dna in a gene, removed during rna splicing after transcription

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14
Q

Exons

A

Coding parts of dna in a gene

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15
Q

Locus

A

The fixed position a gene occupies on a particular dna molecule

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16
Q

Structure of rna

A

Polymer made up repeating mononucleotide subunits, made up of pentose sugar, organic base (a,g,c,u) and a phosphate group

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17
Q

Structure of mRNA

A

Long strand that is arranged in a single helix (base seq of mRNA is determined by the seq of bases on length of dna in process called transcription

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18
Q

Function of mRNA

A

Leaves nucleus + enters cytoplasm + acts as a template for protein synthesis (possesses info in form of codons)

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19
Q

Structure of tRNA

A

Small molecule that is a single stranded chain folded into a clover leaf shape (many types of tRNA each bind to a specific a.a) - sometimes double stranded due to h bonds between bases - has an anticodon loop

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20
Q

Proteome

A

Full range of proteins produced by the genome

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21
Q

Comparison of DNA mRNA and tRNA

A
  • dna = double polynucleotide chain, m + t = single polynucleotide chain
  • dna = largest molecule, m = middle, t = smallest molecule
  • dna = pentose sugar is deoxyribose, m + t = pentose sugar is ribose
  • dna = agct, m + t = agcu
  • dna = found mostly in nucleus, m + t = manufactured in the nucleus but found throughout cell
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22
Q

Describe transcription

A

DNA helicase unwinds the double helix by breaking the h bonds between the bases on the 2 strands. RNA polymerase binds to one of the strands of dna and helps to form phosphodiester bonds and free RNA nucleotides form complementary base pairs. Produces pre - mRNA (occurs in nucleus). In eukaryotes pre mRNA is spliced (introns removed) before leaves nucleus

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23
Q

How is production of mRNA in á eukaryotic cell different to production of mRNA in a prokaryote

A

Pre - mRNA only produced in eukaryotes and splicing only occurs in eukaryotes as eukaryotes have introns, prokaryotes don’t

24
Q

Describe translation

A
  • happens at ribosomes
  • tRNA brings specific amino acids from cytoplasm to ribosome
  • each tRNA has a seq of 3 bases (anticodon)
  • the anti codon forms complementary base pairs with the codon on mRNA (aa is attached at other end of tRNA)
  • ribosomes move along mRNA one codon at a time
  • peptide bonds form between aa and comes of tRNA
25
Role of atp in translation
ATP is hydrolysed to provide required energy (and enzyme used) to form a pepetide bond between 2 aa on the tRNA
26
Define mutation
A change in the base sequence of dna of an organism
27
Define gene mutation
A change to one or more nucleotide bases or change in sequences of bases in dna
28
When do gene mutations occur and what do they include
Spontaneously during dna replication, include base deletion and base substitution
29
What is base substitution
One base changes for another one
30
What is base deletion
One base is lost
31
Consequences of base substitution
1. The formation of a stop codon, which marks end of polypeptide- final protein will be sig diff (shorter + so not perform normal function) NONSENSE MUTATION 2. The formation of a codon for a diff aa, structure of polypeptide is diff by one aa - final protein may differ in shape (bonds 1,2,3 structure) + not function properly e.g enzyme change active site so sub no longer binds MISSENSE MUTATION 3. Formation of codon for same aa, no change to polypeptide - as genetic code is degenerate and so aa have more than 1 codon (most) SILENT MUTATION
32
Consequences of base deletion
- (more sig) - one deleted base causes a frame shift as reading frame that contains 3 letters of the code has been shifted to the left by one letter
33
Other types of mutation that result in frameshift
- insertion (addition) - frameshift to right - duplication of bases - one or more bases are repeated = frameshift to right
34
Other types of mutation
- inversion of bases - group of bases become separated from dna seq and rejoin in same position but other way around - translocation of bases - group of bases become separated from dna seq in one chromosome + become inserted back into another chromosome
35
Define mutagenic agent
Can Inc rate at which mutations can occur (Inc risk) - eg radiation
36
What is nondisjunction
When the chromosomes or chromatids do not split equally during anaphase
37
What is polyploidy
Changes in whole sets of chromosomes - all chromosomes have multiples and cells have no chromosomes in
38
What is anaploidy
Changes in the number of individual chromosomes - an uneven split of chromosomes some cells have more than others
39
Roles of meiosis
1. Producing gamete’s with half no of chromosomes (haploid) 2. Creating genetic variation(“shuffles genes”)
40
Differences between mitosis and meiosis
- mitosis produces diploid cells, whereas meiosis produces haploid cells - mitosis produces genetically identical cells whereas meiosis produces genetically unique cells - mitosis involves 1 div whereas meiosis involves 2 divs - mitosis = 2 cells whereas meiosis = 4 daughter cells
41
What is independent assortment
Occurs in the first division (metaphase 1) and is when homologous pairs line up in random orientations at the equator
42
What is crossing over
Occurs during first meiotic division in late prophase 1. Homologous chromosomes come together as pairs and all 4 chromatids come into contact synapsis occurs (the arms of the chromatids can swap at random, creating many more possibilities for genetic variation of the gametes) they swap at the chiasmata
43
What are the differences between prophase 1 and 2
1 chromosomes become visible + pair up with homologous chromosomes (+ crossing over occurs) whereas 2 chromosomes become visible but do t pair up (already paired) and no crossing over occurs
44
What are the differences between metaphase 1 and 2
1 the homologous chromosomes line up along equator, whereas 2 the chromosomes line up along equator
45
What is the difference between anaphase 1 and 2
1 the homologous pairs are separated, whereas 2 the sister chromatids are separated to either sides of cell
46
What is the difference between telophase 1 and 2
1 2 diploid cells are formed, whereas 2 4 haploid cells are formed
47
What is genetic diversity
The total number of alleles in a population
48
What does greater genetic diversity mean
The greater the genetic diversity the more likely that some individuals in a population will survive an environmental change
49
Why are not all alleles of a population equally likely to be passed onto the next generation
Because only certain individuals are reproductively successful (many die beforehand) and so pass on their alleles
50
Describe natural selection
- within any population of species will be gene pool (with variety of alleles) - random mutation of alleles may result in a new allele of a gene (probably harmful) - however in certain environments new allele may give possessor and adv over those without - will be better adapted and more likely to survive in competition with others - more likely to live longer and breed successfully producing more offspring - new allele is more likely to be passed down to next gen (as more likely to reproduce successfully) - offspring have advantageous allele so more likely to survive and reproduce - happen over many generation so increase in advantageous allele over less advantageous
51
What is directional selection
This occurs whenever the environment changes in a particular way. There is therefore selective pressure for species to change in response to the environmental change.
52
What is stabilising selection
This occurs when the environment doesn't change. Natural selection doesn't have to cause change, and if an environment doesn't change there is no pressure for a well-adapted species to change (characteristics are being preserved)
53
What is an example of directional selection
Bacterial resistance to antibiotics Antibiotics kill bacteria, but occasionally a chance mutant appears that is resistant to that antibiotic. In an environment where the antibiotic is often present, this mutant has an enormous selective advantage since all the normal (wild type) bacteria are killed leaving the mutant cell free to reproduce and colonise the whole environment without any competition.
54
What is an example of stabilising selection
Birth mass of babies It is harmful for an infant to be born with a very low birth weight. Pre-term babies are particularly susceptible to many conditions that can all be fatal and are reflected in high mortality rates at these low birth rates. It is therefore not beneficial to be on the extremes of birth weight. Similarly, delivering a child of too high birth weight can cause complications. Therefore the other extreme of high birth rate is also not beneficial and will not be selected towards. This leads to selective pressures in both directions, stabilising towards a mean birth weight
55
What are anatomical adaptations
Structural features of an organism with Inc chance of survival e.g shorter ears + thicker fur in artic foxes
56
What are physiological adaptations
Processes which occur within the body of an organism which inc chance of survival e.g oxidising of fats rather than carbohydrates in kangaroo rats to produce additional water in dry places
57
What are behavioural adaptations
The way an organism acts with Inc chance of survival e.g autumn migration of swallows from uk to Africa to avoid food shortages in uk winter

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