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Biology > Pack 9 - DNA, genes and protein synthesis > Flashcards

Pack 9 - DNA, genes and protein synthesis Flashcards

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1
Q

Define a gene.

A

A gene is a section of DNA that codes for making a polypeptide or functional RNA.

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2
Q

What is the coded information in a gene in the form of?

A

A specific sequence of bases along the DNA molecule.

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3
Q

What is the name for the particular position in a DNA molecule that a gene is found?

A

Locus

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4
Q

What does a gene code for?

A
  • Sequence of amino acids in a polypeptide.

* Functional RNA including ribosomal RNA and tRNA

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5
Q

How many amino acids occur in proteins in organisms?

A

20

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6
Q

How many bases are present in DNA?

A

4

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7
Q

If four bases are present in DNA and there are 20 amino acids that need to be coded for, what is the minimum number of bases (in a sequence) that code for one amino acid and why?

A

3 - if a sequence of 2 bases coded for an amino acid there would be 4² combinations and therefore DNA could code for 16 amino acids.

If a sequence of 3 bases codes for an amino acid there are 4³ combinations so unto 64 amino acids could be coded for.

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8
Q

What is a triplet?

A

A sequence of 3 bases

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9
Q

How many triplets code for each amino acids?

A
  • Two amino acids are coded for by only one triplet (Trp and Met)
  • Other amino acids are coded for by between 2-6 triplets.
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10
Q

Only 61 of the 64 possible triplets code for an amino acid, what is the role of the other 3 triplets?

A

These are called ‘stop codes’ - they mark the end of a polypeptide chain.

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11
Q

Why is the genetic code known as a ‘degenerate code’?

A

• Most amino acids are coded for by more than one triplet.

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12
Q

Why is the code described as ‘non-overlapping’?

A

Each base in the sequence is only read once. e.g the base sequence:

TACGCT

is read TAC GCT;

and is NOT read TAC ACG CGC GCT.

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13
Q

What is meant by: “the genetic code is universal(with some small exceptions)”? What is this indirect evidence for?

A
  • Each triplet codes for the same amino acid in all organisms (with some small exceptions).
  • Evolution
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14
Q

Why is a triplet always read in the same direction along DNA?

A

If it were read in the other direction it would produce a different triplet and therefore a different amino acid.

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15
Q

Sometimes the amino acid methionine is removed from the start of a polypeptide chain after it has been synthesised, why?

A

The start of a DNA sequence that codes for a polypeptide is always the same triplet - which codes for the amino acid methionine. If it is not needed in the polypeptide is it removed after.

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16
Q

Describe three differences between the structure of DNA in a prokaryotic cell and a eukaryotic cell.

A
  • Prokaryotic DNA is circular; eukaryotic DNA is linear.
  • Eukaryotic DNA is longer.
  • Eukaryotic DNA associates with proteins called histones to from chromosomes.
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17
Q

Describe the structure of DNA contained by chloroplast and mitochondria.

A

Circular with no proteins (like in prokaryotic cells).

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18
Q

When are chromosomes visible?

A

When a cell is dividing.

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19
Q

Describe the structure of a replicated chromosome when it becomes visible.

A

Two sister chromatids joined at the centromere. From an X shape.

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20
Q

How many DNA molecules are there in a chromosome when it first becomes visible and why?

A

Two - it has replicated.

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21
Q

DNA is complexly coiled to form chromosomes. What does DNA initially combine with as it coils?

A

Histone proteins.

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22
Q

How many chromosomes does a human have?

A

46

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23
Q

When the sperm and egg fuses each cell contributes 23 chromosomes (a full set). What is the name of the two chromosomes that carry the same genes (one from each parent)?

A

Homologous pairs.

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24
Q

What is the diploid number?

A

The total number of chromosomes. 46 in humans or 23 homologous pairs.

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25
Q

A homologous pair is always two chromosomes. What is the main similarity between these two chromosomes and what differentiates them?

A
  • They contain the same genes

* They contain different alleles of the genes.

26
Q

Define an allele.

A

A number of alternative forms of a gene.

27
Q

How many alleles of a gene does each individual inherit?

A

2 -one from each parent.

28
Q

How is the information contained in the genetic code of DNA transferred from inside the nucleus to the cytoplasm? (What molecule)

A

messenger RNA

29
Q

Where deos mRNA leave the nucleus? Why can’t DNA leave here?

A
  • Nuclear pores

* DNA is too large

30
Q

What is a codon?

A

A sequence of three bases on mRNA that code for a single amino acid.

31
Q

Define genome.

A

The complete set of genes in a cell (including those in mitochondria/chloroplasts).

32
Q

What is a proteome?

A

The full range of proteins produced by the genome.

33
Q

What is the difference between the proteome and the complete proteome?

A
  • The complete proteome is the full set of proteins produced by the genome.
  • The proteome is the proteins produced by a certain cell under certain conditions.
34
Q

What is the monomer of RNA?

A

Nucleotide

35
Q

Describe the structure of an RNA nucleotide? (3 parts)

A
  • Ribose - pentose sugar
  • an organic base (adenine, guanine, cytosine, uracil)
  • A phosphate group
36
Q

What are the three tupes of RNA in eukaryotic cells?

A
  • messenger RNA (mRNA)
  • transfer RNA (tRNA)
  • ribosomal RNA
37
Q

Describe the structure of mRNA. (2 points)

A
  • Single strand of RNA nucleotides.

* Single helix

38
Q

What determines the sequence of bases on a molecule of mRNA?

A

The sequence of bases on a particular section of DNA from which the molecule of mRNA is transcribed.

39
Q

Describe the shape of tRNA?

A

• Clover leaf shaped

40
Q

How many strands deos tRNA have?

A

One

41
Q

What is the name of the three bases on tRNA that bind to the codon on an mRNA molecule?

A

Anticodon.

42
Q

Where does the amino acid bind to a tRNA molecule relative to the anticodon loop?

A

The opposite side/end.

43
Q

What base does uracil pair with?

A

Adeneine

44
Q

What is the role of the structure of tRNA?

A

Binding amino acids when the anticodon binds to the codon on mRNA.

45
Q

Order the molecules from most to least stable;

  • DNA
  • mRNA
  • tRNA
A
  • DNA
  • tRNA
  • mRNA
46
Q

Where are tRNA and mRNA manufactured?

A

Nucleus

47
Q

What molecule is the product of transcription?

A

pre-mRNA

48
Q

Describe the process of transcription in 5 steps.

A
  • An enzyme acts on a specific region of the DNA causing the two strands to separate - exposing the nucleotide bases.
  • Free RNA nucleotides pair with the complementary DNA nucleotide bases.
  • RNA polymerase moves along the strand and joins the nucleotides together to form a pre mRNA molecule.
  • The RNA polymerase moves along the DNA and the DNA strands rejoin behind it. Leaving about 12 nucleotides exposed at one time.
  • When RNA polymerase reaches a stop triplet, it detaches and the production of pre-mRNA is complete.
49
Q

What bond is formed between RNA nucleotides by RNA polymerase?

A

Phosphodiester

50
Q

What is the template strand of DNA?

A

The strand that the complementary RNA bases of mRNA form from.

51
Q

What is the coding strand of DNA?

A

The strand that has the same bases as those on mRNA. Except thymine instead of uracil.

52
Q

What is an exon and what is an intron?

A

• Exons and introns are sections of DNA within a gene. • Exons code for amino acids; Introns do not.

53
Q

Are Introns found in prokaryotic cells ? Therefore does prokaryotic mRNA require splicing?

A
  • No

* No

54
Q

What is the process of splicing?

A
  • Introns are removed from pre-mRNA

* Exons are joined together to from mRNA

55
Q

What is the difference between pre-mRNA and mRNA?

A

• pre-mRNA contains introns.

56
Q

Describe translation in 7 steps. (information in brackets does not need to be learned)

A
  • A ribosome becomes attached to the starting codon (AUG) at the end of the mRNA molecule.
  • The tRNA molecule with a complementary anticodon (UAC) moves to the ribosome and pairs with the codon on the mRNA. This carries a specific amino acid (methionine).
  • Another tRNA bound to an amino acid - with an anticodon complementary to the next codon on the mRNA - pairs with the codon.
  • The ribosome moves along the mRNA, bringing together two tRNA molecules at a time, each pairing with the corresponding mRNA codons.
  • The two amino acids on the tRNA are joined by a peptide bond using an enzyme and ATP which is hydrolysed to provide the energy.
  • As the ribosome moves on to the third codon, the third and second amino acids bind and the first tRNA molecule is released.
  • This continues until a stop codon is reached. At which point, the ribosome, mRNA and last tRNA separate.
57
Q

What happens to released tRNA molecules after they are used in translation?

A

They bind to another amino acid to be used again.

58
Q

How many (roughly) polypeptides are made from the reading of one mRNA molecule?

A

Up to 50 ribosomes can pass immediately behind the first so 50 polypeptides are made at the same time.

59
Q

Explain why genes indirectly control the activity of a cell?

A

Genes code for mRNA. mRNA determines which tRNA molecules attach to ribosome. tRNA molecules determine which amino acids are Brough to the polypeptide chain. Amino acid sequence determines the polypeptide chain and therefore the protein. This includes enzymes which control cell activities.

60
Q

What happens to the polypeptide chains produced by translation?

A

They are sometimes joined together forming proteins with quaternary structure.

Biology (18 decks)

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