Biology AS-Level Paper 1

• What are the differences between Monosaccharides, Disaccharides and Polysaccharides?


  Monosaccharides: Single sugar molecules. Disaccharides: Two sugar molecules linked together. Polysaccharides: Many sugar molecules linked together in a chain by either 1-4 or 1-6 Glycosidic bonds.
• Example of Polysaccharide: Cellulose

  • Important for structural strength in plants.
  • Long chains
  • Hydroxyl group of carbon 1 is inverted 
  • insoluble 
  • B-glucose molecules joined by 1-4 glycosidic bonds 

   
• Glycogen - stored as energy source in animals (liver & muscle cells) , Contains 1-6 Glycosidic bonds making it a branched molecule
• Amylase enzyme breaks down starch into maltose which can be broken down further to glucose.
• Starch - storage polysaccharide found in plant cells. Contains 1-6 Glycosidic bonds making it branched molecule
• Amylose and Amylopectin in Starch

  Amylopectin contains 1-4 / 1-6 Glycosidic , Rapid energy release

  Amylose contains only 1-4 Glycosidic bonds , Slow energy release
• Examples of Mono/Di/Polysaccharides

  Monosaccharide: Glucose, Fructose , Galactose

  Disaccharide: Sucrose ,Lactose, Maltose

  Polysaccharide: Glycogen, Starch, Cellulose
• what are the functions of a Lipid?

  Energy storage, insulation,

  Water-proofing
• How is a triglyceride formed?

  Through the esterification of glycerol with three fatty acids. (3 Waters are lost)
• what are Unsaturated fatty acids and their properties? -Oils. -Unsaturated fatty acids: contain double C=C bond in their chain causing a kinked chain,

  • liquid at room temperature
  • healthier than saturated fats.
• What are Saturated Fatty acids and their properties ?

  • Fats

  Saturated fatty acids:

  • solid at room temperature
  • Unhealthy fatty acid
• Structure of Phosphlipid ?

  Arranged in Bilayer

  Hydrophillic head

  Hydrophobic tail
• What is an Ester bond?

  Ester bond: formed by the condensation reaction between a carboxyl group of a fatty acid and hydroxyl group of Glycerol
• what is a prosthetic group?

  Non-protein molecule bound to a protein, necessary for its function.

  e.g Haem group for Haemoglobin
• What is the structure of a Fibrous Protein?

  Little to no tertiary structures

  Insoluble in water

  Made of secondary structures
• Quaternary Structure of a protein

  • 3D arrangement of more than 1 polypeptide chain

   

  • composed of subunits 

   

   
• What is the Tertiary Structure?

  • Overall 3D structure of the protein
  • Further folded and contains Hydrogen, disulphide and ionic bonds
• What is the Secondary Structure of a Protein?

  The folding of a polypeptide chain, alpha helix coils and beta pleated sheets held together by H-bonds
• What is the primary structure of a Protein?

  Amino acid polypeptide chain held by peptide bonds
• What is a peptide bond?


  A covalent bond between two amino acids in a protein formed by a condensation reaction between Carboxyl group and amine group
• What is the structure of Collagen ?

  supercoiled triple-helix
• What is the structure of Haemoglobin ?

  Quaternary structure protein

  made up of 4 polypeptide chains each chain containing a Haem group
• Nucleic Acid phosphdiester bond

  Hydroxyl group at C3 bonds to Phosphate group of another nucleotide
• Nucleotide formation

  Condensation reaction between C1 hydroxyl group and NH group from nitrogenous base

   

  Water removed and a Nitrogen-glycosidic bond is formed
• DNA structure

  Double helix with complementary base pairs

  Covalent bonding occurs between nucleotides on the same strand

   

  hydrogen bonds form between nitrogenous based of opposite strands 
• Nucleotide bonding between bases

  Adenine and Guamine are Purine base

   (2 nitrogen containing rings)

   

  Thymine and Cytosine and Uracil are Pyrimidine bases 

  (1 nitrogen containing ring)
• How is DNA replicated?

  Semi-conservative replication.
• What is the process of DNA Replication ?

  1. Helicase unzips DNA

  2. SSB proteins hold open DNA to prevent recoiling

  3. Primer laid by Primase

  4. DNA Polymerase binds to primer, reads strand and lays complementary bases

  5. Leading strand built towards replication fork

  6. Lagging strand built away from rep fork

  7. Lagging strand forms Okazaki Fragment

  8. DNA ligase joins Okazaki Fragments and the sugar phosphate backbone.
• mRNA Structure

  single stranded RNA (base pairs = AU , CG)
• tRNA Structure

  ssRNA , anti-codon for protein synthesis
• Process of Transcription in the Nucleus

  Helicase unzips DNA

  SSB hold open to prevent recoiling

  Primer laid by Primase

  RNA Polymerase reads template strand then lays complementary RNA bases

  Once Stop codon reached ,mRNA detaches from template
• Modifications before Translation

  Poly-A 3’ tail and 5’ cap added

  Introns removed by splicesomes

  mRNA strand then leaves nucleus by nuclear pore.
• Process of Translation

  Once mRNA leaves nucleus, mRNA attaches to ribosome

  Ribosome reads mRNA strand and signals tRNA to collect amino acids

  tRNA complementary anti-codon picks up amino acid from protoplasm

  tRNA brings amino acid back to mRNA strand and forms temporary H-bonds to mRNA strand

  Once more amino acids are brought to ribosome, peptide bonds form

  Once stop codon is read , Ribosome detaches and protein is released

  Then protein undergoes modification before being sent out to where it’s needed
• What is the nature of Genetic Code?

  Triplet codons

  Degenerate (more than 1 triplet codon codes for an amino acid)

  Non-overlapping
• Types of Gene Mutations

  Substitution (point)

  Insertion

  Inversion
• Sickle Cell Anemia

  Substitution mutation occurs which causes RBC to lose their biconcave shape
• What is the Induced fit hypothesis?

  Enzyme-substrate interaction which causes the active site of the enzyme to contour to the shape of the substrate to form a ES-complex
• What do enzymes do?

  Catalyse biochemical reactions by lowering the activation energy needed
• How does temp. affect Enzyme activity ?

  Temp increase initially increases rate of enzyme activity as increase of kinetic energy. However after optimum temp. is reached enzymes denature causing rate of activity to decrease
• What are the properties of water’s dipole nature?

  High SHC

  Polar Solvent

  Surface tension (Cohesion)

  Incompressibility