1.3Unit 1 — Cell Biology
DNA and the Production of Proteins — SQA National 5 Biology — SQA National 5 Biology Revision Notes & Topical Questions
5 min read 2 parts Lesson 3 of 6
Section 1 of 2DNA structure and the genetic code
1DNA (Deoxyribonucleic acid)3 points
:
- Double-stranded molecule twisted into a double helix.
- Composed of repeating nucleotide units with a sugar-phosphate backbone and nitrogenous bases facing inwards.
- Carries the genetic instructions for making proteins needed by all living organisms.
2Complementary base pairing rules3 points
:
- Adenine (A)pairs strictly with Thymine (T).
- Cytosine (C)pairs strictly with Guanine (G).
- Bases are held together by weak hydrogen bonds.
3The genetic code3 points
:
- The sequence of bases along a DNA strand specifies the sequence of amino acids in a polypeptide chain.
- Every triplet of bases (a codon) codes for one specific amino acid.
- The order of amino acids determines the 3D shape and specific function of the resulting protein.
Section 2 of 2The role of mRNA in protein synthesis
1More
DNA is confined to the nucleus and is too large to pass through nuclear pores to the cytoplasm.
2Messenger RNA (mRNA)3 points
:
- Single-stranded molecule complementary to one DNA strand.
- Synthesised in the nucleus during transcription (in RNA, Uracil (U) pairs with Adenine instead of Thymine).
- Carries a complementary copy of the genetic code from DNA in the nucleus out through nuclear pores to a ribosome in the cytoplasm.
3Assembly at the ribosome (translation)2 points
:
- The ribosome reads the mRNA base sequence in triplets.
- Amino acids are brought in and joined in the specified correct order by peptide bonds, assembling the completed protein.
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