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Biology ALevel AQA PAPER 1 > 🩶 3.4 Topic 4 - 3.4.1 DNA, genes and chromosomes > Flashcards

🩶 3.4 Topic 4 - 3.4.1 DNA, genes and chromosomes Flashcards

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1
Q

What is a gene?

A

A sequence of DNA bases that codes for either a polypeptide or functional RNA.
A gene is a section of DNA located at a particular position (locus = fixed position) on a DNA molecule.

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2
Q

The order of what determines the order of amino acids in a particular polypeptide?

A

Bases in a gene.

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3
Q

What is each amino acid coded for by?

A

A sequence of three bases in a gene called a triplet.

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4
Q

If genes do not code for a polypeptide, what do they code for instead? What is what they code for?

A

Functional RNA - RNA molecules other than mRNA, which perform special tasks during protein synthesis.
Examples include tRNA and rRNA which form part of ribosomes.

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5
Q

What are enzymes and what are they responsible for?

A

Proteins and as they control chemical reactions they are responsible for an organism’s development and activities.

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6
Q

Does one DNA molecule carry many genes?

A

Yes.

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7
Q

DNA codes for amino acids but it is made up of …

A

… nucleotides not amino acids.

Each amino acid is coded for by a sequence of 3 bases in a gene called a triplet.

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8
Q

What is the minimum suggested number of bases that code for an amino acid?

A

3.

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9
Q

How many different amino acids occur in proteins?

A

20.

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10
Q

Each amino acid must have its own code of bases on the DNA. True or false?

A

True.

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11
Q

How many different bases are there?

A

4.

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12
Q

What are the 4 different bases?

A

Adenine, Guanine, Cytosine & Thymine.

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13
Q

How many bases produce 64 different codes?

A
  1. 4 different bases and 3 bases code for an amino acid.
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14
Q

How many possible triplets is there?

A

64.

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15
Q

What is the genetic code?

A

The sequence of base triplets (codons) in mRNA which code for specific amino acids.

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16
Q

What does it mean why you say ‘The genetic code is non-overlapping?’

A

Each base in the sequence is only read once, separate from the triplet before it and after it. Base triplets do not share their bases.

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17
Q

What does it mean why you say ‘The genetic code is degenerate?’

A

Some amino acids are coded for by more than one base triplet.

There are more possible combinations of triplets than there are amino acids (20 compared to 64 possible triplets).

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18
Q

What does it mean why you say ‘The genetic code is universal?’

A

The same specific base triplets code for the same amino acids in all living things.
E.g. UAU codes for tyrosine in all organisms.

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19
Q

There are start and stop triplets/codons which are used to tell the cell when to start and stop the production of the protein. They are found at the beginning and end of the mRNA.

A
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20
Q

A triplet is always read in one particular direction along the DNA strand. True or false?

A

True.

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21
Q

What is the amino acid which is at the start of a DNA sequence that codes for a polypeptide?

A

It is always the same triplet. This codes for the amino acid methionine.

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22
Q

How many triplets do not code for any amino acid? and why?

A
  1. These are called ‘stop codes’ and mark the end of a polypeptide chain.
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23
Q

What is the genetic code?

A

The sequence of base triplets (codons) in mRNA which codes for specific amino acids.

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24
Q

What is the word which describes how genes can exist in more than one form?

A

Alleles.

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25
Q

Describe the DNA in prokaryotic cells:

A

DNA molecules are shorter, form a circle and are not associated with proteins called histones. The DNA condenses to fit in the cell by supercoiling.

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26
Q

Describe the DNA in eukaryotic cells:

A

DNA molecules are longer, form a line meaning it’s linear and are associated with proteins called histones to form chromosomes. The DNA is wound up to fit into the nucleus.

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27
Q

Describe the DNA in mitochondria and chloroplasts of eukaryotic cells:

A

Is short, circular and not associated with proteins.

28
Q

What are exons?

A

Sequences which code for amino acids.

29
Q

What are introns?

A

Noncoding sequences which do not code for amino acids.

30
Q

Does prokaryotic DNA have introns?

A

No.

31
Q

What are non-coding repeats?

A

Areas which do not code for amino acids becease they are DNA sequences that repeat over and over outside of genes in eukaryotic DNA.
E.g. CCTTCCTTCCTT.

32
Q

What is the role of messenger RNA (mRNA)?

A

Transfers the DNA code from the nucleus to the cytoplasm and acts as a type of messenger.

33
Q

Is mRNA small enough to leave the nucleus through the nuclear pores?

A

Yes.

34
Q

What is the definition of a codon?

A

The sequence of three bases on mRNA that codes for a single amino acid.

35
Q

What is the definition of a genome?

A

The complete set of genes in a cell, including those in mitochondria and/or chloroplasts.

36
Q

What is the definition of a proteome?

A

The full range of proteins produced by the genome.
This is sometimes called the complete proteome, in which case the term proteome refers to the proteins produced by a given type of cell under a certain set of conditions.

37
Q

What does RNA stand for?

A

RiboNucleic Acid.

38
Q

What is RNA?

A

It is a polymer which is made up of repeating mononucleotide sub-units.

39
Q

What does RNA form?

A

A single strand on nucleotides.

40
Q

What are nucleotides made up of?

A
  • The pentose sugar ribose
  • One of the organic (contains carbon) bases adenine (A), guanine (G), cytosine (C) and uracil (U)
  • A phosphate group.
41
Q

What are the two types of RNA which are involved in protein synthesis?

A
  • Messenger RNA (mRNA)
  • Transfer RNA (tRNA).
42
Q

When is mRNA made?

A

During transcription.

43
Q

What does mRNA carry? & where to and from?

A

It carries the genetic code from the DNA to the ribosomes, where it is used to make a protein during translation.

44
Q

What is the structure of mRNA?

A

It is a single polynucleotide strand.

45
Q

What is the name usually given to three adjacent bases?

A

Codons.

46
Q

What are two other names for codons?

A

Triplets or base triplets.

47
Q

Is mRNA long or short?

A

Long.

48
Q

Where is mRNA produced?

A

In the nucleus.

49
Q

What is the base sequence of mRNA determined by?

A

The sequence of bases on a length of DNA in a process called transcription.

50
Q

How is the structure of mRNA suited to its function?

A

It possesses information in the form of codons (three bases that are complementary to a triplet in DNA).

51
Q

What is a codon?

A

Three bases that are complementary to a triplet in DNA.

52
Q

What does the sequence of codons determine?

A

The amino acid sequence of a specific polypeptide that will be made.

53
Q

When is tRNA made?

A

During translation.

54
Q

What does tRNA carry? & where to and from?

A

It carries the amino acids that are used to make proteins to the ribosomes.

55
Q

What is the structure of tRNA?

A

It is a single polynucleotide strand which is folded into a clover shape.

56
Q

What bonds form between specific base pairs to hold the molecule in its shape?

A

Hydrogen bonds.

57
Q

What does every tRNA molecule have?

A

A specific sequence of three bases at one end called a anticodon.

58
Q

What binding site does tRNA have on their molecule at the other end of the anticodon?

A

Amino acid.

59
Q

Is tRNA a small or large molecule?

A

Small molecule, that is made up of around 80 nucleotides.

60
Q

In RNA what is Thymine replaced with?

A

Uracil.

61
Q

What can RNA join with? and how?

A

RNA can join with DNA as well as other RNA molecules. They can do this through complementary base pairing.

62
Q

Describe the structure, function and composition of DNA? (8)

A
  • Largest molecule of the three
  • Double-helix molecule
  • Pentose sugar is deoxyribose
  • Organic bases are Adenine, Guanine, Cytosine and Thymine
  • Found mostly in the nucleus
  • Quantity is constant for all cells of a species (except gametes)
  • Chemically very stable.
63
Q

Describe the structure, function and composition of mRNA? (8)

A
  • Single polynucleotide strand
  • Molecule is smaller than DNA but larger than tRNA
  • Single-helix molecule (except in a
    few viruses)
  • Pentose sugar is ribose
  • Organic bases are Adenine,
    Guanine, Cytosine and Uracil
  • Manufactured in the nucleus but
    found throughout the cell
  • Quantity varies from cell to cell
    and with level of metabolic activity
  • Less stable than DNA or tRNA, individual molecules are usually broken down in cells within a few days.
64
Q

Describe the structure, function and composition of tRNA? (8)

A
  • Single polynucleotide chain
  • Smallest molecule of the three
  • Clover-shaped molecule
  • Pentose sugar is ribose
  • Organic bases are Adenine,
    Guanine, Cytosine and Uracil
  • Manufactured in the nucleus but found throughout the cell
    -Quantity varies from cell to cell and with level of metabolic activity
  • Chemically more stable than mRNA but less stable than DNA.
65
Q

What are alleles?

A

Different forms of the same gene.

66
Q

What makes alleles different forms of the same gene?

A

The order of bases in each allele is slightly different so they code for slightly different versions of the same polypeptide.

Biology ALevel AQA PAPER 1 (16 decks)

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