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A-level Biology Longridge Towers School > Chapter 8 DNA, Genes and Protein Synthesis > Flashcards

Chapter 8 DNA, Genes and Protein Synthesis Flashcards

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1
Q

What is a gene?

A

A gene is a section of DNA that contains the code for making polypeptides and functional RNA and ultimately proteins.

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2
Q

Give 2 examples of functional RNA.

A

Functional RNA includes ribosomal RNA (rRNA) and transfer RNA (tRNA).

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3
Q

What does the specific sequence of bases in the DNA determine?

A

The specific sequence of bases in the DNA determines the specific sequence of amino acids in the resulting polypeptide (and ultimately protein).

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4
Q

How are genes responsible for controlling all the activities of a cell?

A

Enzymes are proteins that control chemical reactions. By coding for proteins genes are responsible for controlling the activities of the cell.

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5
Q

What is a locus?

A

The particular place that a gene is located on a chromosome is its locus.

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6
Q

What does each set of 3 DNA bases codes for ?

A

Each set of 3 DNA bases codes for 1 amino acid.

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7
Q

What is each set of 3 DNA bases called?

A

Each set of 3 DNA bases is called a triplet.

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8
Q

How many amino acids are there?

A

There are 20 different amino acids.

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9
Q

How many possible triplets are there?

A

There are 64 different possible triplets so most triplets will code for the same amino acid.

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10
Q

What does the statement “DNA is degenerate” mean?

A

DNA code is described as degenerate because most amino acids are coded for by more than one triplet.

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11
Q

What is the START triplet on the DNA?

A

The start triplet on the DNA is always the same: TAC. It codes for methionine but this amino acid is always removed during processing.

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12
Q

What are STOP triplets?

A

There are several STOP triplets which signal the end of the gene.

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13
Q

What do START and STOP triplets signal?

A

START and STOP triplets signal the start and end of the gene.

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14
Q

What does “DNA is non-overlapping” mean?

A

The DNA code is non-overlapping. Bases are read in order in triplets only once.

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15
Q

The triplets in DNA code for the same amino acids in all organisms. What phrase do we use to describe this feature?

A

The genetic code is universal. The triplets in DNA code for the same amino acids in all organisms.

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16
Q

Is nuclear DNA mostly coding or non-coding?

A

In eukaryotes, most of the nuclear DNA does not code for polypeptides. There are, for example, non-coding multiple repeats of base sequences between genes.

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17
Q

What are exons and introns?

A

Within a gene only some sequences, called exons, code for amino acid sequences. Within the gene, these exons are separated by one or more non-coding sequences, called introns.

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18
Q

Describe DNA found in prokaryotic cells.

A

In prokaryotic cells DNA molecules are short and circular.

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19
Q

Which types of cells do not have proteins associated with their DNA?

A

Prokaryotic DNA does not have proteins associated with it.

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20
Q

Which type of cells lack chromosomes?

A

Prokaryotic DNA is not arranged in chromosomes.

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21
Q

What is DNA like in eukaryotic cells?

A

DNA in eukaryotic cells is linear forming chromosomes.

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22
Q

What are the proteins associated with the DNA molecules in eukaryotes called?

A

In eukaryotic cells the DNA molecules have proteins called histones associated with them.

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23
Q

Describe the DNA in mitochondria and chloroplasts.

A

Eukaryotic cells contain mitochondria and sometimes chloroplasts. Mitochondria and chloroplasts contain short, circular DNA with not associated proteins (much like the DNA of prokaryotes).

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24
Q

In which type of cells can chromosomes be found?

A

Chromosomes are only found in eukaryotic cells.

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25
Q

Draw and label a chromosome as it would appear during replication.

A

During mitosis chromosomes replicate and condense resulting in 2 identical chromatids held together by a centromere,

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26
Q

What are chromosomes like when replication is not taking place.

A

When cells are not replicating the chromosomes are not visible and are dispersed throughout the nucleus.

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27
Q

Describe how DNA in chromosomes is associated with histones.

A

DNA in chromosomes is associated with a protein called histones. The strand of DNA winds around the histone proteins.

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28
Q

How many sets of chromosomes do humans have?

A

Eukaryotic organisms like humans formed from sexual reproduction, contain 2 sets of chromosomes. One from each parent.

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29
Q

What word is used to describe an organism with 2 sets of chromosomes?

A

An organism with 2 sets of chromosomes is described as diploid.

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30
Q

What is the diploid number for humans?

A

The diploid number for humans is 46.

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31
Q

How many homologous pairs of chromosomes do humans have?

A

Humans have 23 homologous pairs of chromosomes.

32
Q

What are homologous chromosomes?

A

Homologous chromosomes are chromosomes that code for the same genes.

33
Q

Where do homologous chromosomes come from?

A

One homologous chromosome comes from one parent and the other comes from the other parent.

34
Q

How are homologous chromosomes different from each other?

A

Although homologous chromosomes code for the same genes they may have different forms of the genes (alleles).

35
Q

What do we call different forms of a gene?

A

Different forms of a gene are called alleles.

36
Q

How are alleles different from each other?

A

Different alleles have slightly different base sequences.

37
Q

What do different alleles result in?

A

Differences in allele base sequences result in different phenotypes. Example: blue eyes or brown eyes.

38
Q

How can a new allele arise?

A

A mutation in the base sequence of a gene can result in a new allele.

39
Q

What is the effect of most mutations on proteins?

A

Most mutations result in non-functioning proteins being produced.

40
Q

What are the 3 types of RNA?

A

There are 3 types of RNA: ribosomal RNA (rRNA), messenger RNA (mRNA) and transfer RNA (tRNA).

41
Q

Give 5 ways RNA is similar to DNA.

A

RNA is similar to DNA in that both are:
1. Polymers

  1. Contain a pentose sugar
  2. Contain a phosphate group
  3. Nitrogenous base
  4. Nucleotides are joined by strong phosphodiester bonds.
42
Q

Give 3 ways RNA structure differs from DNA.

A

RNA is different from DNA because it has a ribose sugar instead of a deoxyribose sugar, it has the nitrogenous base uracil instead of thymine and it is single stranded. RNA is shorter than DNA.

43
Q

Where is mRNA assembled? Where does it go?

A

mRNA is assembled in the nucleus through transcription but is small enough to leave through a nuclear pore.

44
Q

What is a primary mRNA strand composed of?

A

A primary mRNA strand in eukaryotes is composed of introns and exons.

45
Q

What is the 3 base code on mRNA called?

A

The 3 base code on mRNA is called a codon. Each codon corresponds to a specific amino acid.

46
Q

What can you consult to work out the amino acid coded for by a specific mRNA codon?

A

It is normally the mRNA code that is used to identify the amino acid order using a table or wheel.

47
Q

How big is tRNA?

A

Transfer RNA (tRNA) is a small molecule of 80 nucleotides.

48
Q

Describe the structure of tRNA.

A

tRNA is folded in a cloverleaf shape which includes some paired bases.

49
Q

What name is given to the 3 exposed bases on the tRNA?

A

tRNA molecules have an anticodon of 3 exposed bases which is complementary to an mRNA codon.

50
Q

How many different types of tRNA molecules are there?

A

There are multiple tRNA molecules - one for each anticodon.

51
Q

What is the role of tRNA?

A

tRNA transfers amino acids. The amino acid it transfers is specific to the anticodon.

52
Q

Where does a specific amino acid bind to the tRNA?

A

There is an amino acid attachment site where a specific amino acid binds to the tRNA.

53
Q

Draw and label a molecule of tRNA.

A

The structure of tRNA is:

54
Q

What is the relationship between codons and anticodons?

A

Anticodons on tRNA are complementary to codons on mRNA.

55
Q

Where in the cell are tRNA molecules found?

A

tRNA is found in the cytoplasm.

56
Q

Describe ribosomes.

A

rRNA is a component of ribosomes. Ribosomes also contain protein. Ribosomes have large and small subunits.

57
Q

Where does transcription take place in the cell?

A

Transcription takes place in the nucleus of a eukaryotic cell and in the cytoplasm of a prokaryotic cell.

58
Q

Name the enzyme involved in transcription and explain what it does.

A

RNA polymerase uses the DNA template strand to bind RNA nucleotides together with strong phosphodiester bonds.

59
Q

What happens when RNA polymerase binds to the DNA at the start codon?

A

Formation of the primary mRNA strand is initiated.

60
Q

What happens when RNA polymerase reaches a stop codon?

A

RNA polymerase stops making mRNA and detaches from the DNA.

61
Q

What is pre-mRNA?

A

Pre-mRNA is the strand of RNA produced from the DNA template in eukaryotic cells before splicing has removed introns.

62
Q

What happens during mRNA splicing?

A

During mRNA splicing introns are removed and exons are joined together to produce a mature mRNA transcript.

63
Q

Why does pre-mRNA need to be spliced?

A

To remove introns.

64
Q

Even though DNA codes for proteins directly, why is mRNA needed to make proteins?

A

DNA is too large to leave the nucleus. A copy is made into mRNA which is small enough to leave the nucleus through a nuclear pore. It also acts to protect the DNA from degradation.

65
Q

Define genome

A

The genome is the complete set of genes in a cell.

66
Q

Define proteome

A

The proteome is the full range of proteins a cell can produce.

67
Q

What is a codon?

A

A codon is the triplet of bases on the mRNA that codes for an amino acid.

68
Q

What type of bond joins amino acids together?

A

Peptide bonds join amino acids together.

69
Q

What is the product of translation?

A

Translation results in the production of a polypeptide.

70
Q

Where does translation take place?

A

Translation takes place in the cytoplasm at a ribosome.

71
Q

What is an anti-codon?

A

An anti-codon is the 3 exposed bases on the tRNA. They are complementary to the codons on the mRNA.

72
Q

Which part of tRNA binds to the mRNA?

A

The anticodon binds to the mRNA codon.

73
Q

What are the stop and start codons for?

A

The stop and start codons are triplets that tell the cell when to start and stop production of the protein. They are found at the beginning and end of the gene.

74
Q

What is a gene?

A

A gene is a section of DNA that contains the code for making polypeptides and functional RNA and ultimately proteins.

75
Q

How can a gene mutation result in a protein not being synthesised properly?

A

One or more incorrect amino acids would be inserted resulting in a change in shape to the protein and affecting its function.

A-level Biology Longridge Towers School (37 decks)

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