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Biology Paper 2 > DNA, genes and chromosomes > Flashcards

DNA, genes and chromosomes Flashcards

1
Q

What is a gene

A

A section of DNA that contains the coded information for making polypeptides and functional RNA

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2
Q

Loci

A

section of DNA located at a particular position

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3
Q

What does a gene code for

A

amino acid sequence of polypeptide, functional RNA, rRNA, tRNA

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4
Q

Only___different amino acids regularly occur in proteins

A

20

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5
Q

What are the main features of the genetic code?

A

degenerate as multiple codons code for the same amino acid, The code is non-overlapping - each base is only read once, the code is universal - each triplet codes for the same amino acid in all organisms

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6
Q

DNA and chromosomes:

A

Differences between eukaryotic and prokaryotic cells -> Pro: dna molecules shorter, circular and not associated with histones

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7
Q

Chromosomes structure:

A

Chromosomes appear as 2 threads joined at a single point -> each thread is called a chromatid (because DNA has already replicated to give 2 identical DNA molecules)

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8
Q

Formation of chromosome:

A

DNA + histones -> DNA histone complex -> coiled -> further coiled and packaged into chromosome

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9
Q

Homologous chromosomes:

A

two chromosomes that carry the same genes but not necessarily the same alleles of the genes

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10
Q

Why are homologous chromosomes important?

A

Each pair is derived from chromosomes provided by egg and sperm

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11
Q

What happens during meiosis to the chromosomes?

A

Halves the number of chromosomes in a way that ensure that each daughter cell receives one chromosomes from each homologous pair.

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12
Q

What is allele?

A

One of a number of alternative forms of a gene

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13
Q

How are alleles structurally different from each other?

A

Allele has a different base sequences, therefore a different amino acid sequence, so produces a different polypeptide

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14
Q

What happens when a mutation occurs?

A

Any changes in the base sequence of a gene produces a new allele of that gene

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15
Q

What is a codon?

A

three bases on mRNA that codes for a single amino acid

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16
Q

What is a genome?

A
  • the complete set of genes in a cell
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17
Q

Proteome

A

full range of proteins produces by the genome

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18
Q

What is the structure of RNA?

A

Polymer up a repeating mononucleotide sub units, made out of: Ribose, AUGC - bases, phosphate group

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19
Q

mRNA structure

A

single stranded linear, removed introns

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20
Q

Function of mRNA:

A

acts as a template for protein synthesis, form codons which determine amino acid sequence.

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21
Q

tRNA structure

A

relatively small molecule, single stranded folded into cloverleaf shape, anti-codon complementary to codon

22
Q

What occurs in transcription?

A

> DNA unwinds to expose the bases to act as a template
only one chain of DNA acts as a template
Unwinding and unzipping is done by DNA > Helicase - which breaks the hydrogen bonds between bases
Free RNA nucleotides in nucleus align opposite exposed complimentary DNA bases
The enzyme RNA polymerase joins together the RNA nucleotide to create new RNA polymer chain.
Splicing occurs to remove introns

23
Q

What occurs in Translation?

A

> once modified mRNA left nucleus - attaches to ribosome in cytoplasm
Ribosome attaches to start codon
tRNA molecule with complimentary anti-codon aligns opposite mRNA held in place by a ribosome.
Ribosome will move along one codon on the mRNA molecule to enable another complimentary tRNA to attach to the next codon
The 2 amino acids delivered by tRNA molecule are joined by a peptide bond, this is catalysed by enzyme + ATP
This continues till stop codon at the end of mRNA molecule

24
Q

What is a mutation ?

A

any change to the quantity or the base sequence of the DNA of an organism

25
What is a gene mutation?
any change to one or ore nucleotide bases or a change in the sequence of bases in DNA
26
How do substitution mutations occur?
A nucleotide in a DNA molecule is replaced by another nucleotide that has a different base -> the popylpetide produce may differ ina single amino acid
27
How do deletion of bases occur?
A nucleotide is lost from normal DNA sequence, which causes a frame shift to the left, this can affect the amino acid sequence and the polypeptide is unlikley to function properly
28
What are the 2 forms of chromosome mutations?
organisms have 3 or more sets of chromosomes rather than usual two (polyploidy - often occurs in plants), individual homologous chromosomes fail to separate during meiosis
29
What are the two ways cell division takes place?
Mitosis produces two daughter cells with the same no. of chromosomes Meiosis produces 4 daughter cells, each with half the number of chromosomes
30
What is the importance of meiosis?
haploid joins to form a diploid allowing to maintain a constant number of chromosomes
31
What is meant by haploid in meiosis
Homologous pairs of chromosomes separate so that only one chromosome from each pair enters a daughter cell
32
Process of Meiosis:
> First division - homologous chromosomes pair up, and their chromatids wrap around each other. Equivalent portions allow for crossing-over to occur. By the end of this division, homologous pairs have separated - with one chromosome from each apir going into one of the 2 daughter cells Second meiotic division: chromatids move apart, four cells usually have been formed
33
How does meiosis lead to genetic variation?
independent segregation of homologous chromosomes, new combinations of maternal and paternal alleles by crossing over
34
Homologous
chromosomes of the same length, with the same genes in the same places
35
What is a gene
length of DNA that codes for a polypeptide
36
Locus
the position of a gene on a chromosomes or DNA molecule
37
Allele
one of the different forms of a particular gene
38
Homologous chromosomes
a pair of chromosomes, one maternal and one paternal that have the same gene loci
39
Independent segregation
homologous pairs arrange themselves in this line; they do so at random -> random combination of chromosomes of maternal and paternal origin and go into daughter cell
40
Crossing over ->
chromatides of each homologous pair become twisted around one another -> equivalent portions of homologous chromosomes that are exchanged -> new genetic combination of material and paternal alleles are produced
41
Genetic diversity
- described as the total number of different alleles in a population
42
Population
- a group of individuals of the same species that live in the same place and can interbreed.
43
What is reduced genetic diversity ->
When a species has fewer different alleles The greater the genetic diversity, the more likely that some individuals in a population will survive an environmental change. Enables natural selection to occur
44
How is allele frequency affected by natural selection?
> Each population has a gene pool with a wide variety of alleles > Random mutation will result in a new allele of a gene -> more advantageous -> more likely to survive -> more success reproduction > Pass on their alleles to the next generation -> gave an advanagtge for survival and is more likely to be passed to next generation > Over many generation, the no of individuals with the new advantageous allele increase, allele frequency increases
45
What is selection?
process by which organisms that are better adapted to their environment tend to survive and breed.
46
Directional selection
selection may favour individuals that vary in one direction from the mean of the population. When the environmental conditions change, the phenotypes that are best suited to the new conditions are most likely to survive. These individuals are more likely to survive and then will be more likely to survive and breed.
47
Stabilising selection
selection may favour average individuals, preserving the characteristics of a population. If environmental conditions remain stable, it is the individuals with phenotypes closest to the mean that are favoured, and they are more likely to pass their alleles on to the next generation.
48
Polygenes
Most characteristics are influenced by more than one gene (polygenes).
49
Anatomical adaptation
shorter ears, thicker fur in artic foxes
50
Physiological
oxidising fat to produce more water
51
Behavioural
autumn migration of swallows from uk to Africa

Biology Paper 2 (12 decks)

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