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Biology A1 & A2 > 4A: Genetic information > Flashcards

4A: Genetic information Flashcards

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1
Q

What are the base pairing rules (in DNA and RNA) ?

A

DNA:

  • A joins to T (2 hydrogen bonds)
  • C joins to G (3 hydrogen bonds)

RNA:

  • A joins to U (U replaces T)
  • G joins to C

Therefore, when discussing the proportions of a particular base, you will always find A=T and C=G

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2
Q

Which end of DNA is DNA polymerase complementary to?

A

It is complementary to the 3’ end

= so it moves in one direction from 3’ to 5’

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3
Q

Draw a nucleotide

A

Phosphate
|
Pentose —- Nitrogenous base
Sugar

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4
Q

What are the functions of the antiparallel strands in DNA? (4)

A
  • Maintains 2 copies of DNA in case of mutation
  • Protects bases
  • Required for semi-conservative replication
  • Improves molecular stability
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5
Q

Describe what a gene is

A

A gene is a base sequence of DNA that codes for:
• the amino acid sequence of a polypeptide
• a functional RNA (including ribosomal RNA and tRNAs).

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6
Q

What do genes do?

A

Genes carry the information to produce the amino acid sequence of a polypeptide

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7
Q

When discovering how DNA bases coded for amino acids, why did scientists suggest that there must be a minimum of 3 bases that coded for each amino acid?

A

Because:

  • Only 20 different amino acids regularly occur in proteins
  • Each amino acid must must have its own code of bases on the DNA
  • Only 4 different bases (A,G,C,T) are present in DNA
  • If each base coded for a different amino acid, only 4 different amino acids could be coded for.
  • Using a pair of bases, 16 different codes are possible, which is still inadequate
  • 3 bases produce 64 different codes, more than enough for 20 amino acids
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8
Q

What is the code (3 bases for each amino acids) called?

A

Each one is called a triplet

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9
Q

What are 2 features of genetic code relating to amino acids coding?

A
  • A few amino acids are coded for by only a single triplet

- The remaining amino acids are coded for by between 2 and 6 triplets each

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10
Q

What is a genome?

A

Complete set of genes in a cell

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11
Q

What is a proteome?

A

Full range of proteins produced by the genome

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12
Q

What is the function of RNA?

A

Transfers coded info from the DNA into the cytoplasm where it can be translated into proteins

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13
Q

What is a codon?

A

A sequence of 3 bases that codes for an amino acid

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14
Q

What are the 3 types of RNA?

A

Transfer - tRNA
Messenger - mRNA
Ribosomal - rRNA

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15
Q

Describe mRNA

A
  • The code for the gene in the DNA molecule is ‘transcribed’ (copied) into an mRNA molecule
  • So mRNA carries the code for a particular polypeptide from the nucleus to the cytoplasm, it can travel through nuclear pores
  • Triplets of bases on the mRNA = codons
  • Single stranded helix
  • Has a short lifetime (is broken down)
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16
Q

Describe tRNA

A
  • Each amino acid is attached to a tRNA with the appropriate anticodon
  • Matches the triplet code in an mRNA molecule to their respective amino acid
  • Short (only 80 nucleotides long)
  • Looped clover-leaf structure
  • On the middle loop there is a triplet base sequence called the anticodon –> it’s complementary to one of the 64 possible codons on the mRNA
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17
Q

Describe rRNA & ribosomes

A
  • Together with proteins forms ribosomes

- Ribosomes have 2 subunits, small and large, and are assembled in the nucleolus of the nucleus

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18
Q

What is transcription?

A

The process of making pre-mRNA using part of the DNA as a template

19
Q

What is the DNA template strand also known as?

A

The coding strand

20
Q

If the coding DNA sequence is CGA, what will the mRNA and tRNA sequences be?

A

Coding DNA sequence: CGA
mRNA sequence: GCU
tRNA sequence: CGA

21
Q

Describe the (6) stages of transcription

A
  1. RNA polymerase binds to a section of the DNA
  2. The hydrogen bonds on the DNA molecule are broken (by DNA helicase which is attached to RNA polymerase) = exposing the bases
  3. The nucleotides on one of the 2 DNA strands, known as the template strand, bind to complementary mRNA nucleotides present in the nucleus (C to G, A to U)
  4. RNA polymerase moves along the strand, joining the nucleotides together to make a pre mRNA molecule
  5. The DNA strands rejoin behind the newly forming strand of pre-mRNA
  6. When the RNA polymerase reaches the stop codon (triplet code), it detaches and the pre-mRNA is complete
22
Q 
DNA is made from sections called \_\_\_\_\_ (protein-coding)
and \_\_\_\_\_ (non- coding)
A

DNA is made from:
Exons = protein-coding
Introns = non-coding

23
Q

During transcription, the code from both _____ and _____ is found in the pre-mRNA

A

Introns and exons

24
Q

Why is splicing not required in prokaryotes?

A

Because prokaryotes DO NOT have introns so splicing is not required.

25
Q

Describe the splicing of pre-mRNA.

A
  • The non-functioning introns are later removed from the sequence of the pre-mRNA
  • The remaining exons are joined together by splicing to form mature mRNA
26
Q

Describe how the same sequence of DNA can code for several different proteins.

Hint:
Exon combinations

A

The exon sections can be joined together in a variety of combinations, so the same sequence of DNA can code for several different proteins.

27
Q

What can affect the splicing of pre-mRNA?

A

Mutations

28
Q

Give an example of a disease that is caused by splicing failures.

A

Alzheimer’s disease is caused by splicing failures, so non-functional polypeptides are made

29
Q

What is translation?

A

The process of converting the codon sequence in the mRNA molecule into an amino acid sequence

30
Q

Describe how mRNA leaves the nucleus

A

mRNA leaves the nucleus via nuclear pore, then synthesises a polypeptide

31
Q

What are the (7) stages of translation?

Hint:
1. mRNA leaves nucleus via nuclear pore after splicing

A
  1. mRNA leaves nucleus via nuclear pore after splicing
  2. A ribosome attaches to the start codon of the mRNA
  3. A tRNA (with the complementary anticodon sequence to the first mRNA codon) pairs with the codon on the mRNA
  4. The ribosome (which has 2 subunits, smaller one on the bottom of the mRNA) has 2 codon binding sites. So 2 tRNA molecules at a time are brought together
  5. A peptide bond forms between the 2 amino acids on the tRNAs with the use of ATP (which is hydrolysed to provide energy)
  6. The ribosome moves along the mRNA to the next codon so the first tRNA is released and a new tRNA arrives at the next codon
  7. This continues with up to 15 amino acids being added each second until a polypeptide chain is built up + a stop codon is reached
32
Q

Describe DNA in prokaryotes

A

In prokaryotic cells, DNA molecules are short, circular and not associated with proteins

33
Q

Describe DNA in eukaryotes

A
  • In the nucleus of eukaryotic cells, DNA molecules are very long, linear and associated with proteins, called histones.
  • Together a DNA molecule and its associated proteins form a chromosome.
34
Q

In eukaryotes, the mitochondria and chloroplasts contain what?

A

The mitochondria and chloroplasts of eukaryotic cells also contain DNA which, like the DNA of prokaryotes, is short, circular and not associated with protein.

35
Q

What is the fixed position that a gene occupies called?

A

A gene occupies a fixed position, called a locus, on a particular DNA molecule.

36
Q

Describe the genetic code in DNA

A

Universal, non-overlapping and degenerate.

37
Q

What is the main difference in translation in prokaryotes vs eukaryotes

A
  • In prokaryotes, transcription results directly in the production of mRNA from DNA.
  • In eukaryotes, transcription results in the production of pre-mRNA; this is then spliced to form mRNA.
38
Q

Why do not all gene mutations result in a change in the sequence of amino acids

A

Due to the degenerate nature of the genetic code, not all base substitutions cause a change in the sequence of encoded amino acids

39
Q

What can mutations produce that meiosis cannot?

A
  • Mutations can produce genetic novelty
  • Independent assortment and crossing over during meiosis and the random nature of fertilisation mixes up allelic combination possibilities but does not produce genetic novelty (no new alleles or genes are produced )
40
Q

Describe why DNA is ‘degenerate’

A

Code is known as ‘degenerate’ because most amino acids are coded for by more than 1 triplet

41
Q

Describe why DNA is ‘universal’

A

The same specific base triplets code for the same amino acids in all living things

42
Q

Which end of DNA is DNA polymerase complementary to?

A

3’ end

43
Q

Translate this DNA code into mRNA and tRNA code:

ACGTGA

A

mRNA: UGCACU

tRNA: ACGUGA

Biology A1 & A2 (19 decks)

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