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Biology A Level > Topic 4: Genetic information, variation and relationships between organisms > Flashcards

Topic 4: Genetic information, variation and relationships between organisms Flashcards

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1
Q

What is a gene

A

A section of DNA that codes for the amino acid sequence of a polypeptide and functional RNA

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2
Q

What is an allele

A

A different form of the same gene

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3
Q

what is the locus

A

the location of a particular gene on a chromosome

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4
Q

describe chromosomes

A

this is how DNA is stored. humans have 23 pairs

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5
Q

what is a homologous pair

A

pair of chromosomes that have the same genes but might have different alleles

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6
Q

how is DNA stored in eukaryotes

A

as chromosomes in the nucleus. they are linear and get tightly wound around histone proteins to create nucleosomes.

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7
Q

how is DNA stored in prokaryotes

A

short and circular supercoiled to fit into the cell

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8
Q

differences between DNA in eukaryotes and prokaryotes

A

E- linear
P-circular

E- wrapped around histones
P-not protein bound

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9
Q

what organelles contain their own DNA

A

mitochondria and chloroplast because they have central reactions. photosynthesis and respiration

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10
Q

how is DNA in the mitochondria and chloroplast similar to prokaryotic DNA

A

DNA is short and circular

Not histone bound

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11
Q

What are three features of genetic code? Explain them

A

Degenerate- each amino acid is coded for by more than one codon

Universal- the same triplet base codes for the same amino acid in all organisms

non overlapping- each base in a gene is only part of one triplet of bases that codes for one amino acids. each codon is read as a discrete unit

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12
Q

how many amino acids are there

A

20

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13
Q

what are the four DNA bases

A

Adenine
Thymine
Cytosine
Guanine

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14
Q

what is the advantage of a degenerate code

A

if a substitution mutation occurs, the triplet base may be different but it will still code for the same amino acid.

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15
Q

advantage of a universal code

A

allows genetic engineering to occur e.g production of insulin

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16
Q

advantage of a non overlapping code

A

if a point mutation occurs, it will only affect one codon so just one amino acid

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17
Q

what is an intron

A

sections of DNA that do not code for amino acids. not found in mRNA or prokaryotic DNA

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18
Q

what is an exon

A

section of DNA that codes for an amino acid

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19
Q

genome vs proteome

A

the genome is an organisms complete set of DNA in one cell while the proteome is the full range of proteins in one cell
The genome should never change but the proteome changes quite often

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20
Q

what is the structure of RNA

A

polymer of a nucleotide formed of a ribose, a nitrogenous base and a phosphate group

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21
Q

what is the function of RNA

A

to copy and transfer genetic information

combines with proteins to create ribosomes

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22
Q

what are the types of RNA

A

messenger
transfer
ribosomal

23
Q

what are purine bases

A

Adenine and Guanine. They have double ring structures

24
Q

what are pyrimidines

A

Thymine, Uracil, Cytosine. single ring structures

25
Q

what bond joins nucleotides

A

phosphodiester bonds

26
Q

what are the stages of protein synthesis

A

transcription and translation

27
Q

describe the structure of mRNA

A

long single strand
base sequence is complementary to DNA
each codon set match a codon on DNA and tRNA

28
Q

describe the structure of tRNA

A

clover leaf shape

has an anti codon on the opposite end specific to the amino avid that it attaches to

29
Q

what happens during transcription

A

a molecule of mRNA is made in the nucleus

30
Q

what happens during translation

A

amino acids join together to form a polypeptide chain

31
Q

explain the process of transcription

A
  1. DNA helix unwinds to expose the bases to act as a template
  2. One chain is the template.
  3. This is catalysed by DNA helicase which breaks the H bonds
  4. free mrna nucleotides align opposite complementary bases
  5. RNA polymerase joins rna nucleotides to create a new polymer chain
32
Q

explain the process of translation

A
  • mRNA attaches to a ribosome and tRNA collects amino acids from the cytoplasm to the ribosome.
  • tRNA is a single stranded molecule with a binding site at one end so it can only carry one type of amino acid, and an anti codon.
  • tRNA attaches itself to mRNA by complementary base pairing
  • The amino acids attached to two tRNA molecules join by a peptide bond and then tRNA molecules detach themselves from the amino acids, leaving them behind
33
Q

what is a mutation

A

any change to the base sequence of DNA

34
Q

what is a substitutIon mutation

A

this is when one nucleotide in the DNA sequence is replaced by another. A substitution may not always be harmful as the substituted nucleotide may code in that triplet for the same amino acid.

35
Q

what is a deletion (frameshift) mutation

A

a deletion event is when a nucleotide in the DNA sequence is lost. The loss of a single nucleotide can have a significant impact as it leads to a frame shift, resulting in completely different amino acids being coded for.

36
Q

what are two types of chromosome mutations

A

polyploidy and non-disjunction

37
Q

what is a polyploidy mutation

A

changes in the whole set of chromosomes. when organisms ,have 3 or more sets of chromosomes rather than 2.

38
Q

what is a non disjunction mutation.

A

When chromosomes fail to separate properly during anaphase of meiosis.

39
Q

what are two types of cell division and the main difference

A

mitosis produces two identical daughter cells and meiosis produces 4 genetically different cells

40
Q

what happens in meiosis 1

A

homologous chromosomes pair up and chromatids wrap around each other.chromatids may exchange by crossing over.The cell then divides whereby each daughter cell contains one chromosome from each homologous pair.

41
Q

what happens in meiosis 2

A

chromatids. move apart producing 4 daughter cells

42
Q

how is genetic variation achieved in meiosis

A

-independent segregation of homologous chromosomes (there are various combinations of chromosome arrangement. During meiosis 1 homologous chromosomes line up in pairs, the arrangement of these pairs is random, meaning that the division into the daughter cells is also random.)
-crossing over between homologous chromosomes When pairs of chromosomes line up they can exchange some of their genetic material. Crossing over occurs when one chromosome may swap
places with the same part of its homologous pair leading to a different combination of
alleles on the gene.

43
Q

what is genetic diversity

A

number of different alleles of genes in a population.

44
Q

what is a population

A

a group of individuals of the same species that live in the same place and are able to breed with one another.

45
Q

what isnatural selection

A

process in which fitter individuals who are betted adapted to the environment survive and pass on the advantageous genes to future generations

46
Q

what is evolution

A

Evolution is the process by which the frequency of alleles in a gene pool changes over time as
a result of natural selection

47
Q

what are the types of selection

A

directional and stabilising

48
Q

what is directional selection

A

when the advantageous allele is coding for extreme traits

49
Q

what is stabilising selection

A

individuals with alleles towards the middle range are more likely to survive and reproduce

50
Q

two organisms belong to a species if…

A

If they are able to produce fertile offspring

51
Q

list the hierarchy of taxa

A 
Domain
Kingdom
Phylum
Class
Order
Family
Genus
Species
52
Q

what is species richness

A

a measure of the number of different species in a community.

53
Q

what is biodiversity

A

the variety of living organisms in an area

54
Q

what reduces biodiversity

A

monoculture
pesticides and herbicides
woodland clearance
hedgerow removal

Biology A Level (2 decks)

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