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A Level Biology Paper 1 > Section 4 : DNA, genes, chromosomes and protein synthesis > Flashcards

Section 4 : DNA, genes, chromosomes and protein synthesis Flashcards

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1
Q

What are some differences between eukaryotic and prokaryotic DNA?

A
  • Eukaryotic: Long, linear, associated with proteins called histones, tightly coiled into chromosomes
  • Prokaryotic: Short, circular, not associated with proteins
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2
Q

What is the DNA of prokaryotic cells similar to?

A
  • Mitochondria and Chloroplast DNA
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3
Q

What is a gene?

A
  • Sequence of DNA that codes for amino acid sequence in a polypeptide chain and functional RNA e.g ribosomal RNA and tRNA
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4
Q

What is a locus?

A
  • When a gene occupies a fixed position on DNA molecules
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5
Q

What is the nature of genetic code?

A
  • Universal: The same specific DNA base triplet codes for the same amino acids in all living organisms
  • Non-overlapping: Discrete, each base can be used in 1 triplet/ read once
  • Degenerate: The same amino acid can be coded for by more than 1 codon
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6
Q

In DNA what are the non-coding sections called?

A

Introns

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7
Q

What is the genome?

A
  • The complete set of genes in a cell
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8
Q

What is the proteome?

A
  • The full range of proteins that a cell/ genome can make
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9
Q

What are alleles?

A
  • A version of a gene
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10
Q

What is a homologous pair?

A
  • Same size chromosomes with same genes but different alleles
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11
Q

What are the 2 stages in protein synthesis?

A
  • Transcription - produces mRNA from DNA in the nucleus
  • Translation - produces polypeptides from codons carried by mRNA in the cytoplasm on ribosomes.
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12
Q

What is mRNA?

A
  • Made by transcription in the nucleus
  • Acts as a template for translation
  • Straight chain molecule
  • Chemically unstable - breaks down in few days
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13
Q

What is tRNA - transfer RNA?

A
  • Carries an amino acid from amino acid binding site
  • Anticodon complementary to codon
  • Single polynucleotide strand - leafed clover shape
  • Held together by hydrogen bonds
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14
Q

What is the similarity between mRNA and tRNA?

A
  • Both single polynucleotide strand
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15
Q

What are the differences between mRNA and tRNA?

A
  • mRNA - single helix, straight/ tRNA - clover shaped
  • mRNA - longer, variable length/ tRNA - shorter
  • mRNA - no paired bases or hydrogen bonds/ tRNA does
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16
Q

What is the process of transcription?

A
  • Hydrogen bonds are broken by DNA helicase which separates the double helix
  • RNA nucleotides bind by complementary base pairing
  • RNA polymerase joins adjacent nucleotides together in a condensation reaction. Forming phosphodiester bonds
  • When RNA polymerase reaches stop codon, pre-mRNA detaches from DNA
  • Splicing removes introns - produces mRNA - leaves via nuclear pore
17
Q

Does prokaryotic DNA have introns?

A

No

18
Q

What is the process of translation?

A
  • At the ribosome, tRNA anticodon binds to mRNA codon as it is complementary
  • Brings the correct amino acid
  • 2 amino acid joins in a condensation reaction forming a peptide bond - using ATP
  • tRNA detaches, ribosome moves along to next codon.
  • Continues until stop codon (polypeptide released)
19
Q

What is the role of ATP in translation?

A
  • Hydrolysis of ATP releases energy
  • For the bond between the amino acid and its corresponding tRNA - amino acid attaches to amino acid binding site
  • For peptide bond formation between amino acids
20
Q

What is the role of tRNA in translation?

A
  • tRNA attaches and transports a specific amino acid in relation to anticodon
  • tRNA anticodon complementary base pairs to mRNA codon, forming hydrogen bonds
  • 2 tRNAs bring amino acids for the formation of peptide bonds
  • About 60 types of tRNA to carry 20 different amino acids - degenerate
21
Q

What is the role of ribosomes in translation?

A
  • Attaches to mRNA and houses tRNA, allowing codon-anticodon complementary base pairing
  • Allows peptide bonds to form between amino acids
22
Q

Exam Question: Ricin causes the death of cells and is very poisonous to many animals. Suggest how the action of ricin on ribosomes could cause the death of cells.(2)

A
  1. Prevents mRNA/tRNA binding
  2. Prevents formation of peptide bond
  3. Consequence of loss of identified protein
23
Q

Exam Question: Ricin is found in high concentrations in the seeds of some species of plant. Suggest and explain 1 advantage of this to the plant.(2)

A
  • Animals that can eat the plant get ill/ killed
  • So seeds/plants more likely to survive

A Level Biology Paper 1 (15 decks)

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