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AS Biology > 4A - DNA, genes and chromosomes > Flashcards

4A - DNA, genes and chromosomes Flashcards

1
Q

What is nuclear eukaryotic DNA like?

A

Linear and associated with proteins.

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2
Q

Eukaryotic cells contain linear DNA molecules that exist as what?

A

Chromosomes.

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3
Q

What are chromosomes?

A

Thread-like structures, each made up of one long molecule of DNA.

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4
Q

Where are chromosomes found?

A

In the nucleus.

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5
Q

How can the DNA molecule fit into the nucleus?

A

It has to be wound up as it is really long.

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6
Q

What is the DNA molecule wrapped around to fit into the nucleus?

A

Proteins called histones.

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7
Q

Apart from providing a base for DNA to wrap around, what is the function of histone proteins?

A

Help support the DNA.

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8
Q

After the DNA has been wound up to fit into the nucleus, what happens to the DNA?

A

The DNA (and protein) is then coiled up very tightly to make a compact chromosome.

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9
Q

What organelles in eukaryotic cells also have their own DNA?

A

The mitochondria and chloroplasts.

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10
Q

What is the DNA like in mitochondria and chloroplasts?

A

Pretty similar to prokaryotic DNA because it is circular and shorter than DNA molecules in the nucleus.

It is not associated with histone proteins.

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11
Q

What is prokaryotic DNA like?

A

DNA molecules are shorter and circular.

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12
Q

How do prokaryotes carry DNA?

A

As chromosomes.

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13
Q

How does prokaryotic DNA fit into the cell?

A

It condenses to fit in the cell by supercoiling.

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14
Q

What is a gene?

A

A sequence of DNA bases that codes for either a polypeptide or functional RNA.

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15
Q

What does the sequence of amino acids in a polypeptide form?

A

The primary structure of a protein.

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16
Q

What do different polypeptides have in terms of amino acids?

A

A different number and order of amino acids.

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17
Q

What determines the order of amino acids in a particular polypeptide?

A

The order of bases in a gene.

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18
Q

What does the order of bases in a gene determine?

A

The order of amino acids in a particular polypeptide.

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19
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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20
Q

What is a triplet?

A

A sequence of three bases in a gene.

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21
Q

What does a triplet do?

A

Codes for an amino acid.

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22
Q

What is the first stage in making a polypeptide/the first stage of protein synthesis?

A

DNA is first copied into messenger RNA (mRNA).

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23
Q

What is an amino acid made up of?

A

A sequence of 3 bases in a gene.

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24
Q

What do genes that don’t code for a polypeptide do instead?

A

Code for functional RNA.

25
Q

What is functional RNA?

A

RNA molecules other than mRNA, which perform special tasks during protein synthesis, e.g. tRNA and ribosomal RNA (rRNA), which forms part of ribosomes.

26
Q

What is a genome?

A

The complete set of genes in a cell.

27
Q

What is a proteome?

A

The full range of proteins that the cell is able to produce.

28
Q

Genes that do code for polypeptides contain what?

A

Sections that don’t code for amino acids called introns.

29
Q

What are introns?

A

Sections of a DNA/gene that don’t code for amino acids.

30
Q

What are all the bits of a gene that code for amino acids called?

A

Exons.

31
Q

What are exons?

A

All the bits of a gene that code for amino acids.

32
Q

When are introns removed from DNA?

A

During protein synthesis.

33
Q

Why are introns removed during protein synthesis?

A

So they don’t affect the amino acid order.

34
Q

Does prokaryotic DNA have introns?

A

No.

35
Q

Does eukaryotic DNA have introns?

A

Yes.

36
Q

What is the purpose of introns?

A

The purpose isn’t known for sure.

37
Q

What does eukaryotic DNA contain outside of genes?

A

Regions of multiple repeats.

38
Q

Where are regions of multiple repeats found?

A

Outside of the genes in eukaryotic DNA.

39
Q

What are multiple repeats?

A

DNA sequences that repeat over and over.

E.g. CCTTCCTTCCTT.

40
Q

What are the regions of multiple repeats outside of genes called?

A

Non-coding repeats.

41
Q

What are non-coding repeats?

A

Repeat areas that don’t code for amino acids for example multiple repeats outside of genes.

42
Q

Genes can exist in different forms called what?

A

Alleles.

43
Q

What is an allele?

A

A different form of a gene.

44
Q

What is the order of bases in each allele like?

A

Slightly different.

45
Q

What does the order of the bases in different alleles being different mean they do?

A

They code for slightly different versions of the same polypeptide.

46
Q

How many alleles of the gene that determines blood type are there?

A

3 - one determines O, one A and one B.

47
Q

How many pairs of chromosomes do humans have?

A

23.

48
Q

What are pairs of matching chromosomes called?

A

Homologous pairs.

49
Q

What is a homologous pair?

A

A pair of matching chromosomes.

50
Q

Describe the chromosomes in a homologous pair:

A

Both chromosomes are the same size and have the same genes, although they could have different alleles.

51
Q

Alleles coding for the same characteristic will be found where on each chromosome in a homologous pair?

A

At the same fixed position (locus) on each chromosome in a homologous pair.

52
Q

What is diploid number?

A

The number of chromosomes - 46 in humans.

53
Q

What are antiparallel strands in DNA?

A

The strands run in opposite directions so their 3’ and 5’ ends are at opposite ends.

54
Q

Describe what a gene is

A

A gene is a unit of heredity. A section of DNA on homologous chromosomes at a specific position (the locus). Carries the information to produce the amino acid sequence of a polypeptide.

55
Q

Describe what is meant by the term ‘homologous chromosomes’?

A

In eukaryotes each normal body cell contains 2 copies of each type of chromosome (homologous pairs).

56
Q

What is meant by the diploid number?

A

Humans have 46 chromosomes (diploid number) i.e. 23 homologous pairs.

57
Q

What is an allele?

A

A version of a gene.

58
Q

Define the term mutation?

A

Any changes in the base sequence of a gene produces a new allele for that gene. This will lead to the production of a different polypeptide, and therefore a different protein. This protein may not function properly or at all (eg. enzyme).

AS Biology (47 decks)

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