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AQA A Level Biology COPY > Genetic information, variation and relationships between organisms > Flashcards

Genetic information, variation and relationships between organisms Flashcards

(85 cards)

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1
Q

Describe the appearance of DNA molecules in prokaryotic cells

A

Short, circular, unassociated with proteins

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2
Q

Describe the appearance of DNA molecules in eukaryotic cells

A

Very long, linear, associated with proteins called histones

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3
Q

What are histones?

A

The proteins associated with DNA molecules in eukaryotic cells

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4
Q

What is a gene?

A

A base sequence of DNA that codes for:
the amino acid sequence of a polypeptide
a functional RNA

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5
Q

What is a locus?

A

A term used to refer to the fixed position a gene occupies on a particular DNA molecule

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6
Q

Which 3 key terms describe the genetic code?

A

Universal, non-overlapping, degenerate

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7
Q

Why is the genetic code ‘degenerate’?

A

Most amino acids are coded for by more than one triplet

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8
Q

What is a triplet codon? (in terms of DNA)

A

A sequence of three DNA nucleotide bases which code for a specific amino acid

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9
Q

Only introns code for amino acid sequences. True or false?

A

FALSE. Only EXONS code for amino acid sequences

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10
Q

Genetic code is referred to as ‘non-overlapping’. What does this mean?

A

Each base in the sequence is read only once

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11
Q

Genetic code is generally ‘universal’. What does this mean?

A

Bar a few minor exceptions each triplet codes for the same amino acid in all organisms.

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12
Q

Which feature of genetic code is indirect evidence of evolution?

A

The universal nature of genetic code

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13
Q

What are stop codons?

A

Three bases (one codon) that do not code for any amino acids

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14
Q

During splicing, what part of the pre-mRNA is got rid of?

A

Introns

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15
Q

What is a homologous pair of chromosomes?

A

A pair of chromosomes containing one maternal and one paternal chromatid joined at the centromere. They carry the same genes but may have different alleles

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16
Q

What is an allele?

A

A different version of the same gene

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17
Q

What is the genome?

A

The complete set of genes in a cell (including those in the mitochondria and/or chloroplast

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18
Q

What is the proteome?

A

The full range of proteins produced by the genome

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19
Q

How does the complete proteome differ from the proteome?

A

The complete proteome is the full range of proteins produced by a given cell type under certain conditions

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20
Q

Give three differences between DNA and mRNA

A

DNA is double stranded, mRNA is single
DNA has a double helix, mRNA has a single
DNA has deoxyribose pentose sugar, mRNA has ribose
DNA has AGCT, mRNA has AGCU
DNA is v stable, mRNA is less stable than DNA
DNA’s quantity is constant for all cells of a species (bar gametes), mRNA’s quantity varies from cell to cell w/ level of metabolic activity

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21
Q

‘Double stranded’ describes the structure of DNA, mRNA or tRNA?

A

DNA

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22
Q

‘Single stranded’ describes the structure of DNA, mRNA or tRNA?

A

mRNA and tRNA

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23
Q

Which is the largest structure of tRNA, mRNA and DNA?

A

DNA

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24
Q

Which is the smallest structure of DNA, tRNA and mRNA?

A

tRNA

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25
Which structure, of DNA, tRNA and mRNA has a double helix?
DNA
26
Which structure, of DNA, tRNA and mRNA has a single helix?
mRNA
27
Which structure, of DNA, tRNA and mRNA has a clover shape?
tRNA
28
Which structure, of DNA, tRNA and mRNA has a deoxyribose pentose sugar?
DNA
29
Which structure, of DNA, tRNA and mRNA has a ribose pentose sugar?
mRNA and tRNA
30
Which structure, of DNA, tRNA and mRNA has the bases: adenine, uracil, guanine and cytosine?
mRNA and tRNA
31
Which structure, of DNA, tRNA and mRNA has the bases: adenine, thymine, guanine and cytosine?
DNA
32
Which structure, of DNA, tRNA and mRNA is mostly found in the nucleus?
DNA
33
Which structure, of DNA, tRNA and mRNA is made in the nucleus but can be found throughout the cell?
mRNA and tRNA
34
Which structure, of DNA, tRNA and mRNA is the most stable?
DNA
35
Which structure, of DNA, tRNA and mRNA is the least stable?
mRNA
36
What is transcription?
The process of making pre-mRNA using part of the DNA as a template
37
Describe how pre-mRNA is formed from DNA
Transcription DNA helicase breaks H bonds b/w bases to allow the strands to unwind and expose the bases Free nucleotide bases pair w/ their complementary bases on one of the strands (template strand) RNA polymerase attracted to promoter region on the strand --> goes along joining the nucleotides (phosphodiester bonds) together to form pre-mRNA As RNA polymerase moves along, DNA rejoins behind it RNA polymerase detaches until it reaches a stop codon
38
What is the role of RNA polymerase in transcription?
To join free nucleotides to those on the template strand
39
Messenger RNA (mRNA) is used during translation to form polypeptides. Describe how mRNA is produced in the nucleus of a cell (6) PPQ
1. Helicase; 2. Breaks hydrogen bonds; 3. Only one DNA strand acts as template; 4. RNA nucleotides attracted to exposed bases; 5. (Attraction) according to base pairing rule; 6. RNA polymerase joins (RNA) nucleotides together; 7. Pre-mRNA spliced to remove introns
40
What is splicing?
The process by which introns are removed from pre-mRNA to form mRNA
41
What is translation?
The process by which mRNA is used to make an amino acid chain, and so a protein
42
Describe what happens during translation
A ribosome attaches to the starting codon atone end of the mRNA molecule tRNA molecule w/ the complementary anticodon moves the the ribosome and pairs w/ the codon on mRNA Another tRNA w/ the complementary anticodon for the next codon pairs The 2 amino acids on the tRNA are joined by a peptide bond using an enzyme and ATP Ribosome moves one codon along the mRNA - 1st tRNA released, another joins Process repeats, building up a chain until the ribosome reaches a stop codon
43
What is a gene mutation?
Any change to one or more nucleotide bases, or a change in base sequence
44
What is a base substitution mutation?
When a nucleotide is replaced by another nucleotide with a different base
45
What is a deletion mutation?
When a nucleotide is lost from the normal DNA sequence | Results in a frame shift - all bases shifted forward resulting in different sets of triplets and so different code
46
How many chromosomes does a human somatic cell contain?
46 (23 pairs)
47
What are the stages of meiosis?
Meiosis I and meiosis II, each containing prophase, metaphase, anaphase and telophase
48
What happens during prophase I?
Chromosomes shorten/thicken to become visible Nuclear envelope disintegrates Homologous pairs associate w/ each other (line up next to each other) Crossing over occurs
49
What does crossing over involve?
The exchange of of alleles b/w chromatids/chromosomes
50
What happens during metaphase I?
Chromosomes line up at the equator --> independent assortment (random position in the line) Spindle fibres attach to the centromere
51
What happens during anaphase I?
Chromosomes are pulled apart to opposite poles by the spindle fibres
52
What happens during telophase I?
Spindle fibres disintegrate | Cytokinesis begins - cell splits in 2
53
What happens during prophase II?
Spindle fibres start to form at poles
54
What happens during metaphase II?
Chromosomes line up at the equator | Spindle fibres attach to the centromere
55
What happens during anaphase II?
Sister chromatids pulled away by spindle fibres
56
What happens during telophase II?
Cytokinesis - cell splits (now have 4 genetically different) | Nuclear envelope reforms
57
How does genetic variation occur in meiosis?
Independent segregation/assortment Crossing over Random fertilisation
58
What is genetic diversity?
The total no. of different alleys in a population | Also a factor in allowing natural selection to occur
59
Describe and explain how natural selection leads to evolution
W/in any population there will be a gene pool containing a wide variety of alleles Random mutation --> possibly results in new allele Most cases = harmful but sometimes advantageous w/ allele = better adapted and so more likely to survive Therefore more likely to successfully breed (more likely to get resources, grow more rapidly) and so produce offspring Only those who successfully reproduce will pass on their alleles to the next gen. therefore advantageous allele more likely to be passed on These offspring are also more likely to survive and reproduce successfully Over time, frequency of advantageous increases, non-advantageous decreases
60
What is directional selection?
Where one extreme is favoured over others, causing the allele frequency to shift in the direction of that phenotype
61
What is stabilising selection?
Where individuals w/ phenotypes closest to the mean are favoured (if environmental conditions remain stable) Phenotypes at the extremes are less likely to pass on their alleles, therefore extremes tend to be eliminated
62
Define what is meant by the term 'species'
A group of anatomically, biochemically and genetically similar organisms that are capable of interbreeding to produce gentle offspring
63
What are the two ways of classifying a species?
Artificial classification | Phylogenetic classification
64
How does artificial classification work?
Groups based on their analogous/comparable characteristics e.g. wings
65
What are two problems with artificial classification?
No genetic relation More differences than similarities Doesn't show how they're related
66
How does phylogenetic classification work?
Base upon evolutionary r/ships b/w organisms and their ancestors Groups using shared features derived from ancestors Arranges groups into hierarchy
67
State the phylogenetic hierarchy from largest to smallest
Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species
68
Using the binomial system of naming, what does the 1st name represent?
The genus of the organism
69
Using the binomial system of naming, what does the 2nd name represent?
The species of the organism
70
Why is courtship behaviour important?
To ensure mating is successful and offspring have the max. chance of survival
71
Describe how courtship behaviour can help ensure successful mating
``` Enables individuals to: Recognise members of their own species Identify a mate that is capable of breeding Form a pair bond Synchronise mating Become able to breed ```
72
Explain how being able to recognise members of their own species increases the chance of successful mating and so offspring survival
Only members of the same species produce fertile offspring
73
Explain how being able to synchronise mating increases the chance of successful mating and so offspring survival
Time at which there's the max. probability of sperm and egg meeting
74
Define 'biodiversity'
A general term used to describe variety in the living world
75
What is species diversity?
A term to refer to the no. of different species and the no. of individuals of each species w/in any on community
76
What is genetic diversity?
A term to refer to the genes possessed by the individuals that make up a population of a species
77
What is ecosystem diversity?
A term used to refer to the range of different habitats, from a small local habitat, to the whole earth
78
What is species richness?
The no. of different species in a particular area at a given time
79
What is index of diversity a measure of?
Species richness
80
How do you calculate index of diversity?
d = N(N-1) / Total n(n-1) where: d = index of diversity N = total no. of organisms of all species n = total no. of organisms of each species
81
Describe and explain how agricultural ecosystems affect species diversity
Specific species grown to increase productivity, thus reducing allele variation Increase no. of specific species to make it economical --> area has room for only so much biomass, and if the majority of this is the specific species, that doesn't leave much room for others --> therefore increases competition Pesticide use actively excludes unwanted species Overall species richness decreases
82
Give 5 examples of farming techniques that reduce species diversity
``` Removal of hedgerows Creation of monocultures Filling in of ponds Drainage of marshes and other wetlands Overgrazing of land Use of pesticides and inorganic fertilisers Escape of effluent (sewage/liquid waste) into water courses Absence of crop rotation ```
83
Give 5 examples of conservation techniques
Maintain existing hedgerows at the most beneficial height/length Plant hedges as field boundaries rather than using fences Maintain existing ponds and create new where possible Plant native trees on land w/ a low species diversity Reduce use of pesticides --> bio control where possible or GM crops Use of organic fertilisers Use of crop rotation that includes a nitrogen fixing crop
84
Name 4 ways someone could investigate diversity
``` Look at: observable characteristics DNA base sequences mRNA base sequences protein amino acid sequences ```
85
Give two limitations of using observable characteristics to investigate diversity
Large no. of characteristics coded for by more than one gene Vary continuously Characteristics can also be modified by the environment

AQA A Level Biology COPY (11 decks)

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