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

Genetic information, variation, and relationships between organisms Flashcards

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1
Q

Give 4 properties about the DNA in prokaryotes

A
  1. Short 2. Circular 3. Not associated with protein 4. Do not form chromosomes
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2
Q

Give 4 properties about the DNA in eukaryotes

A
  1. Very long 2. Linear 3. Associated with proteins called histones 4. Together a DNA molecule and its associated proteins can form a chromosome
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3
Q

What is the DNA like in mitochondria and chloroplasts?

A

Short, circular, not associated with protein and does not contain introns

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4
Q

What is a chromosome?

A

During cell division in eukaryotes , DNA and histones are organised into structures called chromosomes

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5
Q

What is a gene?

A

A sequence of DNA bases that codes for the specific amino acid sequence of a polypeptide

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6
Q

Describe homologous chromosomes in 5 points

A
  1. Diploid cells have chromosomes in pairs. One from each parent 2. A homologous pair carries same genes in the same loci but not the same alleles 3. A gene occupies a fixed position, locus, on a DNA molecule or chromosome 4. A gene can exist in different forms called alleles 5. Consists of a maternal and paternal chromosome
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7
Q

What is a base triplet?

A

A sequence of three nucleotide bases

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8
Q

What does a base triplet code for?

A

One amino acid

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9
Q

What are base triplets called in mRNA?

A

Codons

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10
Q

How many different types of base triplets are there?

A

64

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11
Q

How many types of amino acids are there?

A

20

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12
Q

What is a stop code referring to in an amino acid chain?

A

Indicates the end of a code or specific polypeptide

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13
Q

What does non-overlapping mean in terms of the genetic code?

A

Each base is only read once as part of a specific triplet

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14
Q

What does the term ‘universal’ mean in terms of genetic code?

A

The same triplets code for the same amino acids in all organisms

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15
Q

What two types of base sequences do not code for polypeptides and describe them?

A
  1. Introns - Base sequences present in genes but do not code for amino acids 2. Multiple repeats - some of the base sequences present between genes, often consists of the same base sequences occurring again and again
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16
Q

What are exons?

A

The base sequences in genes that do code for amino acids

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17
Q

How does RNA differ in structure to DNA?

A
  1. The pentose is ribose not deoxyribose 2. The organic base uracil replaces thymine 3. mRNA and tRNA are single stranded
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18
Q

Give two properties of mRNA, what it is involved in and where and how it is formed

A
  1. Has a linear structure and contains codons 2. Involved in protein synthesis 3. Formed in the nucleus during transcription
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19
Q

How many different types of tRNA is found in the cytoplasm?

A

At least 20

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20
Q

What type of shape does a tRNA molecule have and why?

A

‘Clover leaf’ shape due to the presence of hydrogen bonds between complimentary bases pairs

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21
Q

What is at either end of a tRNA molecule?

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A

At one end there is an anticodon - 3 unattached tRNA nucleotide bases. At the other end, a binding site for the attachment of a specific amino acid

22
Q

Give four differences in the structure of mRNA and tRNA

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A
  1. mRNA: Linear structure, tRNA: Clover leaf structure 2. mRNA: possesses codons, tRNA: possesses an anticodon 3. mRNA: No hydrogen bonds present, tRNA: Hydrogen bonds present 4. mRNA: No amino acid binding site, tRNA: Amino acid binding site present
23
Q

What is the genome?

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A

The complete set of genes (and the non-coding DNA) in a cell

24
Q

What is the proteome?

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A

The full range of proteins that a cell is able to produce

25
What are the two processes that protein synthesis can be divided into?
Transcription and translation
26
What is transcription?
Occurs in the nucleus and involves rewriting (transcribing) part of the DNA code into a strand of mRNA
27
What is translation?
Occurs in the cytoplasm and involves ribosomes synthesising proteins using information provided by mRNA
28
Describe transcription in 7 points
1. Occurs in the nucleus and involves 'rewriting' (transcribing) part of the DNA code into a strand of mRNA 2. The relevant section of the DNA molecule uncoils and the two strands are separated as hydrogen bonds are broken 3. One of these two strands acts as a template 4. Individual RNA nucleotides line up alongside the DNA nucleotide bases on the template strand by complementary base pairing 5. Uracil pairs with adenine 6. The individual RNA nucleotides are then joined together with phosphodiester bonds in reactions catalysed by RNA polymerase to produce polynucleotide strand 5. The two strands of DNA in nucleus join back together once mRNA has been produced
29
What are exons?
Sections of the gene that code for the polypeptide
30
What are introns?
Sections of the gene that does not code for the polypeptide
31
Describe the process of slicing of pre-mRNA
The mRNA formed during transcription using DNA containing both exons and introns is known as pre-mRNA, the splicing of pre-mRNA involves the removal of introns and the joining together of the exons to form mRNA
32
True or False: Splicing does occur in prokaryotes
False: Splicing does not occur in prokaryotes as their DNA does not contain introns
33
Where does the spliced mRNA go after it has been spliced?
Leaves the nucleus through the nuclear pore and attaches to a ribosome in the cytoplasm where translation occurs
34
Describe what occurs during translation in 6 steps
1. The mRNA binds to a ribosome in the cytoplasm 2. A tRNA molecule with the complementary anticodon base sequence, binds to the first codon on the mRNA strand at the ribosome. The ribosome has two binding sites so that two tRNA molecules will bind to two codons on the mRNA within a ribosome 3. The amino acid on the first tRNA molecule attaches to the amino acid on the second tRNA molecule by a peptide bond in a condensation reaction. This requires hydrolysis of ATP to release energy and an enzyme that is part of the ribosome 4. The first tRNA molecule then moves away from the ribosome, leaving the amino acid behind. It collects another molecule of the same amino acid from the 'amino acid pool' in the cytoplasm 5. The ribosome moves along the mRNA and other tRNA molecules then join in the order determined by the codons on the mRNA strand 6. This process continues along the mRNA strand until all the codons have been 'read' up to the stop codon and the specific polypeptide has been produced
35
What does the polypeptide do after it has been produced during translation?
Folds itself into its secondary and tertiary structure
36
What is genetic diversity?
The number of different alleles in a population
37
What four things is genetic diversity caused by?
Gene mutations, meiosis (independent segregation of homologous chromosomes and crossing over, random fusion of gametes during fertilisation and chromosome mutations
38
What are gene mutations?
Changes in the sequence of nucleotide bases. New alleles of genes are produced by mutations
39
How might gene mutations be caused?
Gene mutations occur spontaneously, they might arise during DNA replication
40
What can gene mutation rate be increased by?
Mutagenic agents e.g. X-rays, benzene, UV light
41
What can gene mutations result in?
A different amino acid sequence in the encoded polypeptide, this is due to the altered base sequence coding for a different sequence of amino acids
42
What are the seven types of gene mutations?
Substitution, deletion, addition, duplication, inversion and translocation of bases
43
What is substitution?
The replacement of one or more bases by one or more different bases
44
What can the substitution of a single base result in?
A new triplet coding for a different amino acid in the polypeptide chain which may result in a non-functional protein being formed OR one different amino acid in the polypeptide changes but a functional protein is still produced OR the same amino acid may be coded for due to the degeneracy of the DNA code so the polypeptide remains unchanged
45
What is deletion?
The removal of one or more bases
46
What can deletion result in?
A frame shift, which is the alteration in all the triplets from the point of mutation, the sequence of amino acids is altered from the point of mutation and therefore the protein formed is nearly always non-functional
47
What is addition?
The adding of one or more bases
48
What does addition result in?
A frame shift, which is the alteration in the base triplets from the point of addition, the sequence of amino acids is altered from the point of addition and the protein formed is non-functional
49
What is duplication?
Where one or more bases is repeated
50

AQA Biology A-Level (2 decks)

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