AS UNIT 1 BIOLOGY

• • nucleotides join by condensation reactions
  • they form phosphodiester bonds along a sugar phosphate backbone
• DNA

  • deoxyribonucleic acid
  • double stranded
  • carries genetic code
  • Capable of self replication

  RNA

  • ribonucleic acid
  • single stranded
  • assists in the functioning of DNA

  
• Bonding/pairing

  • dna= adenine +thymine, guanine+cytosine
  • RNA= adenine+ uracil, guanine and cytosine
• the bases on one chain pair up with complementary bases on another chain
• The two strands of dna run antiparallel (opposite direction)
• Hydrogen bonding increases stability between the strands of nucleotides
• proteins

  haemoglobin=

  -globular proteins found in red blood cells

  -each molecule consists of 4 polypeptides, 2 alpha and 2 beta chains

  • each polypeptide has an iron containing haemoglobin group attached
  • important in the transport of oxygen in animals
• collagen

  • fibrous protein
  • each molecule consists of 3 similar polypeptides coiled round each other and held together by hydrogen bonds
  • collagen molecules are bonded to form the strong fibres in skin, tendons and ligaments
• proteins contain-

  • carbon
  • hydrogen
  • sulfur
  • nitrogen
• chains of amino acids

  contain:

  • an amino group
  • a carboxylic group
  • a hydrogen atom
  • a residual (R) group-> differs the amino acids
• what is this?

  
• amino acids can bond together to form a dipeptide

  a condensation reaction is involved and the amino acids are linked by a covalent peptide bond

  hydrolysis reaction breaks the peptide down to release the 2 amino acids

  many amino acids are bonded to form a polypeptide
• structures

  • primary structure- sequence of amino acids
  • secondary structures- alpha helix or beta pleated sheets
  • tertiary structure- globular proteins, 3D shape, due to international with free R groups and amino acids
  • quaternary structure- 2 or more polypeptide chains bonded together
• splitting and bonding of proteins

  
• prions

  • disease causing proteins
• how does prions disease arise?

  1. transmission- the rough consumption of infected food or via an open wound exposed to an environment
  2. inheritance- of a gene mutation that would have occurred during meiosis in the production of an egg or sperm cells
  3. sporadically- where normal proteins spontaneously transform into the disease form
  4. The disease is known as sporadic if there is no evidence of it being inherited or transmitted via an external source
• what do prions do?

  malformed proteins called prions cause diseases known as

  • transmissible spongiform encephalopathics—> diseases in which the brain tissue becomes spongy with holes
  • involves the replacement of a normal glycoprotein with a structurally altered prion
• presence of prions in body—

  • causes normal protein to alter its secondary structure
  • then a chain reaction is set up
  • leads to accumulation of prions on neurone surfaces
  • causes neurone degeneration and cell death
• dna replication

  genetic code-

  • achieved by self replication using the semi conservative mechanism in each strand
  • each strand acts as a template for the synthesis of the new strand
  • each new strand contains one of the original strands and a new strand
• DNA replication sequence

  • dna helicase breaks the hydrogen bonds and unzips part of the double helix revealing 2 strands
  • DNA polymerase moves along each strand, acting as a template for synthesis of a new strand
  • DNA polymerase catalyses the joining of free nucleotides to each of the exposed original strands by base pairing. Complementary strands form
  • the process of unzipping and joining new nucleotides continues along whole length
• Evidence for semi conservative replication

  nelson and stahl

  • grew bacteria in a medium where nitrogen was supplied
  • the dna of bacteria became entirely heavy
  • bacteria got transferred to a normal light isotope immediately before changing the mediums at intervals at successive generations. Samples were removed and dna was extracted
  • analysis involved centrifugation
• Dna replication

  
• enzymes-

  influences of enzymes=

  • substrate concentration
  • enzyme concentration
  • temperature
  • pH levels

  enzyme molecules need to combine with/ collide with substrate molecules so substrate concentration and temperature influences the rate of reaction

  enzymes are globular proteins with a precise tertiary structure so factors that influence protein shape like temp and pH will influence the reaction
• how enzymes work

  1. lock and key model
  2. induced fit model -> enzyme moulds itself around the substrate
• chemical reactions of an organism are called metabolism

  catabolism= breakdown reactions

  anabolism= build up reactions

  enzymes are proteins that catalyse metabolic reactions
• theory of enzyme action

  - to catalyse an reaction, an enzyme and substrate must collide to form an enzyme-substrate complex

  catalysis takes place on the enzyme surface

  E+S-> ES->EP->E+P

  enzymes are-

  specific-> determined by tertiary structure

  reactions take place on active site
• anabolic reactions-

  • substrate molecules are orientated so that there is bonding between them on the active site

  catabolic reactions-> formation of active site around substrate assists breaking of bonds
• Effects on enzymes

  pH on enzyme activity-

  at low ph a Hugh conc of H+ causes -charged R groups to lose charge

  at high pH a low conc of H+ causes +charged groups to lose their charge

  changes from the optimal ph cause a decreased in enzyme activity. This is because the nature of the protein and so the active site of the enzyme are altered by changes in ph

  ionic bonds in tertiary structure are disrupted

  ph is a measure of H+ conc and as the conc of hydrogen ions changes, the charges on R groups of amino acids are altered
• effect of temperature

  1. at low temp an inc in temp causes an inc in enzyme activity. an inc in temp provides more kinetic energy for collisions and complexes
  2. at high temp an inc in temp causes a sharp decrease in enzyme activity. this is due to the bones holding the tertiary structure of enzyme mol are broken + so the active site loses its comp shape for substrate attachment. enzyme is denatured
• substrate conc

  at low sub cono, an inc in conc will increase enzyme activity- it is the limiting factor. This is because because increased conc of sub molecule will increase collisions with enzyme molecules = complexes are formed

  at high sub conc, an inc in concentration does not cause an increase in enzyme activity. at inc sub conc, enzymes are fully employed and so at any time all active site are occupied
• enzyme concentration

  an increase in conc increases the rate of reaction. At high enzyme conc activity may level off but only if there is insufficient substrate

  This is because an increase in conc of enzyme molecules increases the chance of successful collisions with substrate molecules
• enzyme inhibitors

  • molecules that bind to enzymes and decrease their activity

  competitive inhibitor-> closely resembles the structure of the substrate and so competes for the active site but does not remain there permanently

  
  

  non competitive-> does not resemble the substrate, may act in different ways

  • binds to a part of the enzyme away from the active site, altering the shape of the enzyme molecule including the active site.
  • inhibitor may leave the enzyme so that the active site regains its catalytic shape
  • inhibitors bind to the enzyme molecule, leaving enzyme permanently damaged
• Effects of competitive inhibitor

  • inhibitor and substrate both compete for active site
  • more substrate available, more likely substrate will find an active site
  • If sub conc increases, effect of inhibition decreases
• effect of non competitive inhibitor -

  • not fighting for active site
  • increase in sub conc does not effect decrease effect of inhibitors
• Immobilised enzymes

  • occurs when it is confined so cannot move but still acts on substrate
  • facilitates the use o continuous flow column reactions->
  • Reactions can constantly take place
  • product is enzyme free- purification costs are reduced
  • enzyme remains separate, can easily be reused
  • enzyme is supported- stability is improved. Remains active over a range of ph and temp
• methods of immobilisation

  1. absorption onto insert support
  2. covalent bonding onto solid support e.g cellulose fibres
  3. cross linking via a binding chemical
  4. encapsulation in a partially permeable membrane
  5. entrapment inside a gel
• diagnostic reagent strips as biosensors

  • use immobilised enzymes to detect or monitor a particular molecule
  • molecule reacts with a specific immobilisation enzyme that the reaction causes a colour change or is converted into an electrical signal
  • glucose test strips- used to test for presence of glucose in urine. degree of colour change shows amount of glucose present
  • glucose meters- measure level of glucose in a blood droplet. It is placed on a test strip, the amount of gluconic acid produced is converted into electrical signals and is presented as a digital readout
• Enzymes as bio markers of disease

  • during injury or disease of an organ, damaged tissue will release its enzymes-> then measuring the level of enzymes in the body fluids into which they may be released. Can be used for diagnosis
• Biomarkers

  • Creatine leaking into blood from damaged heart muscle
  • Esterase in urine indicating white blood cell activity in urinary tract infection
  • Elastase in respiratory tract during infection
• Creatine leaking into blood


  Indicates heart muscle injury