Unit 3 AOS1

• What are the similarities between DNA and RNA?

  • Made up of monomers called nucleotides
  • Both possess four bases
  • Both have a phosphate sugar backbone
• What are the differences between DNA and RNA?

  • Their difference in sugars (deoxyribose and ribose)
  • DNA is double-stranded, whereas RNA is single-stranded
  • DNA has base Thymine, whereas RNA has base Uracil
• Give a brief description of tRNA?

  • Carries an specific amino acid
  • Contains an anticodon, a complementary code that binds with codons from mRNA to release amino acids from tRNA and form a peptide through condensation polymerisation
  • Synthesised in the nucleus
• Give a description of rRNA?

  • Combines with proteins to form the main structural component in ribosomes
  • Make up the large & small subunits in ribosomes
  • Synthesised in the nucleolus
• What is the structure of DNA?

  • Double helix
  • Phosphate sugar backbone formed by a phosphodiester bond (strong covalent bond)
  • Antiparallel
  • Complementary base pairing
• Adenine contains two hydrogen bonds with Thymine/Uracil

  Guanine contains three hydrogen bonds with Cytosine
• Which of the following are purines (two carbon nitrogen ring bases)/pyrimidines (one carbon nitrogen ring base)?

  Purines: Adenine & Guanine

  Pyrimidines: Cytosine & Thymine & Uracil
• Explain condensation polymerisation of nucleotides

  • The reaction that joins nucleotides together is know as a condensation polymerisation reaction
  • The bond that combines phosphate & sugars is a phosphodiester bond
  • When phosphate and sugar bonds, a molecule of water is released (condensation) making a polymer (polymerisation), forming the phosphodiester bonds
• What is a proteome?

  The complete set of proteins expressed by the genome of an individual cell or organism
• Primary Structure

  • Sequence of amino acids
  • The shape of the protein, and therefore its function is determined by the primary structure (because of the sequence of amino acids)
  • Held together by peptide bonds
• Secondary Structure

  • When a polypeptide chain folds and coils by forming hydrogen bonds between peptide backbones of amino acids
  • Secondary structure is characterised by alpha helices, random coiling and beta pleated sheets
• • Random coils - Irregular section of the polypeptide that form between alpha helices and beta pleated sheets
• Tertiary Structure

  • Proteins fold into their 3D shape due to the characteristics of the amino acids in the polypeptide chain
  • There are several types of bonds responsible for this:

  Hydrogen bonds form between R groups

  
  

  Disulfide bonds form between cysteine amino acids - provides strength and stabilises the 3d structure

  
  

  Ionic bonds form between charged amino acids
• For a protein to be functional, it needs to at least be a tertiary structured protein

  The specific shape of a protein determines its function (e.g enzyme, receptor etc)
• Quaternary Structure

  • When two or more proteins of tertiary structure join together
  • Not all proteins have quaternary structure
• • Polypeptide chains with a prosthetic group attached are also considered to have quaternary structure
  • A prosthetic group is a non-protein group such as an ion or vitamin bound to a protein
• H H O

  I I II

  N - C - C - OH

  I I <---------- Central carbon

  H R

  Amino R- Carboxyl

  Groups
• The characteristics of each amino acid are determined by the R-group (E.g an amino acid with a hydrophobic R-group is more likely to form bonds with another amino acid with a hydrophobic R-group)
• • Amino acids are joined together by peptide bonds formed by condensation polymerisation
  • During this process, an H2O molecule is released, while a polymer (polypeptide) is formed
• Genetic code is:


  • Universal: Nearly all living organism use the same rules & codons to code for proteins
  • Degenerate: Different codons can code for the same amino acid
  • Unambiguous: Codons can only code for a single amino acid
  • Non-overlapping: Each triplet or codon is read independently of adjacent triplets or codons / each nucleotide is part of only one codon