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Biology A-level > Biology Chapter 8 > Flashcards

Biology Chapter 8 Flashcards

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1
Q

What is a gene?

A

A section of DNA that contains the coded information for making polypeptides and functional RNA

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2
Q

Where is the gene located on the DNA

A

Locus

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3
Q

What is the genetic code?

A

A set of rules used by living cells to translate information encoded within genetic material into proteins

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4
Q

Define degenerate

A

Most amino acids are coded for by more than one base triplet

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5
Q

Define non-overlapping

A

Each base in the sequence is read only once

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6
Q

Define universal

A

Each triplet codes for the same amino acid in all organisms (with a few minor exceptions), which is indirect evidence of evolution

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7
Q

Give 3 differences of eukaryotic and prokaryotic cells

A

Eukaryotic cells:

  • Longer DNA molecules
  • DNA molecules are linear
  • DNA associated with proteins (histones) to form chromosomes

Prokaryotic cells:

  • Shorter DNA molecules
  • DNA molecules are circular
  • DNA is not associated with proteins
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8
Q

How is DNA packed into chromosomes?

A
  1. DNA combined with histones and a DNA-histone complex is coiled
  2. The coils fold to form loops and the loops coil and pack together to form the chromosome
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9
Q

Define genome

A

The complete set of genes in a cell including those in the mitochondria/chloroplasts

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10
Q

Define proteome

A

The full range of proteins produced by the genome

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11
Q

Define diploid

A

Full amount of chromosomes

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12
Q

Define haploid

A

Half amount of chromosomes

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13
Q

Describe transcription

A
  1. DNA helicase attaches to the DNA double helix at the beginning of the gene. The hydrogen bonds between the 2 DNA strands are broken, separating the strands, and the DNA molecule uncoils at that point, exposing some of the bases
  2. The RNA polymerase lines up free RNA nucleotides alongside the exposed bases on the template strand. The free bases are attracted to the exposed bases. Complementary base pairing means that the mRNA strand ends up being a complementary copy of the DNA template strands (except the base T is replaced bu U) in RNA). Once the RNA nucleotides have lined up with specific bases on the DNA strand, they’re joined together by RNA polymerase, forming an mRNA strand
  3. The RNA polymerase moves along the DNA, assembling the mRNA strand. The hydrogen bonds between the uncoiled strands of DNA re-form once the RNA polymerase has passed by and the strands coil back into a double helix
  4. When RNA polymerase reaches a particular sequence of DNA (stop signal), it stops making mRNA and detaches from the DNA. In eukaryotes, mRNA moves out of the nucleus through a nuclear pore and attaches to the ribosome in the cytoplasm, where the next stage of protein synthesis takes place
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14
Q

Describe splicing of pre-mRNA

A

DNA of genes is made up of exons and introns. Exons = coding parts of DNA and so they are joined together. Introns = non-coding parts of DNA and so they are removed. Introns would therefore, prevent the synthesis of a polypeptide. Splicing is also needed because the mRNA molecules are too large to diffuse out of the nucleus through the nuclear pores

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15
Q

Describe translation

A
  1. The mRNA attaches itself to a ribosome and tRNA molecules carry amino acids to it. ATP provides the energy needed for the bond between the amino acid and tRNA to form
  2. A tRNA molecule carrying an amino acid, with an anticodon that’s complementary to the first codon on the mRNA, attaches itself to the mRNA by complementary base pairing. A second tRNA molecule attaches itself to the next codon on the mRNA in the same way
  3. The two amino acids attached to the tRNA molecules are joined by a peptide bond. The first tRNA molecule moves away, leaving its amino acid behind
  4. A third mRNA molecule binds to the next codon on the mRNA. Its amino acid binds to the first two and the second tRNA molecule moves away. This process continues, producing a chain of amino acids, until there’s a stop signal on the mRNA molecule
  5. The polypeptide chain (protein) then moves away from the ribosome and translation is complete
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16
Q

Give 3 differences of mRNA and tRNA

A

mRNA = Linear shape
No base pairing
No binding site for amino acids

tRNA = Clover leaf shaped
Base pairing
Binding site for amino acids

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17
Q

Describe the structure of proteins

A

A protein is a polymer of amino acids joined by peptide bonds formed by condensation reactions

Primary structure = Order of amino acids in polypeptide chain

Secondary structure = Alpha helix or beta pleated. Folding of polypeptide chain, due to hydrogen bonds

Tertiary structure = Arrangement of amino acids in polypeptide chain. Ionic/disulfide bonds involved. 3D

Quaternary structure = More than 1 polypeptide chain

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18
Q

Starting with mRNA in the nucleus of a cell, describe how a molecule of protein is synthesised

A
  1. mRNA leaves nucleus through nuclear pore
  2. mRNA goes to the ribosomes
  3. tRNA molecule brings amino acids to ribosomes
  4. Specific tRNA molecule for specific amino acid
  5. Anticodon on tRNA corresponds to codon on the mRNA
  6. Peptide bond between amino acids
  7. tRNA detaches and collects another amino acid
  8. Ribosome moves along mRNA
19
Q

At what stage in the cell cycle would errors in copying DNA bases occur?

A

DNA replication

20
Q

Is DNA stored differently in eukaryotes and prokaryotes?

A

Yes

21
Q

What is a chromosome?

A

Linear DNA and associated proteins

22
Q

What is a histone?

A

A protein - DNA is wound around it

23
Q

What is the function of histones?

A

To support the DNA

24
Q

What is the difference between prokaryotic and eukaryotic DNA?

A

Prokaryotic DNA is circular and not wound around histones

25
Q

How is prokaryotic DNA stored to fit in a cell?

A

Supercoiled

26
Q

Which eukaryotic organelles contain DNA similar to prokaryotic DNA?

A

Mitochondria and chloroplasts

27
Q

What is the primary structure of proteins?

A

The sequence of amino acids

28
Q

How many bases code for 1 amino acid?

A

3

29
Q

What are the 3 bases that code for 1 amino acid called?

A

Triplet/codon

30
Q

What is functional RNA?

A

RNA (other than mRNA) which performs special tasks during protein synthesis

31
Q

Give 2 examples of functional RNA

A

tRNA and rRNA

32
Q

Other than for a protein, what else does DNA code for?

A

Functional RNA

33
Q

Do prokaryotes have introns?

A

No

34
Q

What is a non-coding multiple repeat?

A

Repeating DNA sequences outside of the gene which do not code for a protein

35
Q

What is an allele?

A

Different form of a gene

36
Q

If the gene is for blood type, what are the 3 possible alleles?

A

A, B, O

37
Q

Are the order of bases the same in these alleles

A

No, slightly different

38
Q

How many pairs of chromosomes do humans have?

A

23 pairs

39
Q

What are homologous chromosomes?

A

Matching pairs of chromosomes with the same genes

40
Q

Do homologous chromosomes have the same genes?

A

Yes

41
Q

Do homologous chromosomes always have the same alleles?

A

No

42
Q

How is the shape of tRNA held together?

A

Hydrogen bonds between the specific base pairs

43
Q

What are the 2 specific sites on tRNA?

A

Amino acid binding site and anticodon

Biology A-level (14 decks)

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