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What are six functions of proteins and give example
- transport: hemoglobin binds to oxygen + transport
- movement: myosin caises contraction o muscle fibres w/ actin
- hormones: insulin binds to receptors in plasma memb. o target cells causing them to remove glucose fr blood
- defence: immunoglobin act as antibodies to inactivate/destroy foreign antigens
Explain significance of polar and non-polar amino acids (3)
- controlling position of proteins in membranes
- creating hydrophilic channels through membranes
- specificity o active sites in enzyme
- polar have hydrophilic r group, non polar opp
Explain non polar / polar AA for position o proteins in membranes
- polar aa found on parts protein molecule tt protrude fr membrance b/c water exists there, in ECF and cytoplasm
- non polar Aa found in parts o membrane proteins embedded in plasma membrane = keeps proteins embedded /stabilizes structure
- polar aa create channels in transport proteins where hydrophilic substance can diffuse through P.M.
specificity o active sites in enzymes (polar/non polar aa)
- If the amino acids in the active site of an enzyme are non-polar -> active site specific to non-polar substrates
- if the active site = polar amino acids then the active site is specific to a polar substance
- AA w/ postively charged r groups -> attract negatively charged substrate ions; vice versa
hydrophilic channels through membranes
- polar aa on surface o proteins make them water soluble
- non polar aa in centre = stabilize
- non polar aa cause proteins to remain embedded in membranes
- polar aa create channels which hydrophilic substances can dissolve
- biological catalysts for chemical reactions
- Are globular proteins (tertiary or quaternary structure)
- Have active site where the specific substrates bind
- Influence stability of bonds in the reactants, can form bonds (anabolic)or break bonds (catabolic)
- affected by temperature, pH,
lowers activation energy o chemical reaction
- Region on the surface of an enzyme to which substrates bind
- catalyzes a chemical reaction involving the substrates.
similarities lock and key model and induced fit model for enzyme activity
- both involve quaternary/tertiary protein w/ an active site
- lowering o activation energy in chemical reaction
- product detaches fr active site after reaction
differences lock and key model and induced fit model for enzyme activity
- LK: assumes active site and sub match exactly
- IF: not exactly
- LK: substrate fits exactly into active site
- IF: induced after binding
- LK: active site fits only one substrate
- IF: several similar but different substrates can bind
lock and key model
- assumes active site and sub match exactly, not other molec fit or attracted
- enzyme lock, sub key
- enzyme sub collide; sub binds
- active site catalyzes chemical reaction
- sub turns into product and detaches
induced fit model
- until substrate binds, active site doesnt fit sub exactly
- sub approaches active site w/ KMT
- shape of active site changes as sub approaches and binds
- then fits exactly
- sub induces change in enzyme which weakens sub bonds -> product
- detaches fr enzyme b/c doesnt fit active site anymore
- several diff but similar sub can bind to one enzyme
- structural change in protein that results in loss (usually permanent) of biological properties
- caused by heat and pH
what four factors affect enzyme activity?
- enzyme concentration
- substrate concentration
- if plenty substrate available, increasing enzyme concentration increase reaction rate
- direct positive correlation
- if concentration enzyme fixed and conc. substrate increase, rate o reation will increase then level
- enzyme becomes saturated as active sites filled
temperature effect on enzyme activity
- higher temperatures increas rate o collision b/twn sub and enzyme
- reaction rate increase
- however few can tolerate temp above 50 - 60 degress cel
- enzymes have optimal temp
- above, heat denatures enzyme
pH on enzymes
- all have optimum pH generally b/twn 6 and 8
- extremes o pH reduce enzyme activity
- both acids and bases denature enzymes
explain use o lactase in production o lactose free milk
- example o industrial process depending on biotech
- methods are huge and increasing economic importance
- lactose naturally in milk, -> changed into glucose + galactose by lactase
- people intolerant can't produce those enzymes;= diarrhea, cramps, bloating
- can consume lactose free milk produced using lactase obtained fr yeast, naturally grows in milk
- lactase extracted fr yeast, purified sold as immobilized enzyme
- milk passed through column lactase, breaks down lactose = lactose free milk w/o lactase
- lactase can be added as well
what do metabolic pathways consist of?
Metabolic pathways consist of chains and cycles of enzyme-catalysed reactions.
how do enzymes lower the activation energy of the chemical reactions that they catalyse?
- Most reactions are exothermic
- energy released by the new bonds formed is less than the activation energy.
- Reactants of a chemical reaction need to gain energy (activation energy) before they can undergo the reaction.
- needed to break bonds within the reactants.
- substrate changed into transition state, diff fr trasition state during reaction when enzyme not involved
- transition state w/ binding to active site has less energy and is how enzymes reduce activation energy
- later stage in the reaction energy will be released as new bonds form.
competitive w/ ref to ex
- competitive: inhibiting molecule structurally similar to substrate binds to active site, competes w/ substrate binding
- inhib folic acid synthesis in bacteria by prontosil
- can be overcome by increasing substrate concentration, increases chance that sub binds to enzyme
non competitive inhibition and ex
- non competitive: binds to enzyme, not active site, causes conformational change
- change in active site -> reduces effectiveness or makes it unable to bind at all
- does not compete directly for active site
- sub cant prevent binding o inhibitor despite concentration so maximum enzyme activity rate lower than no inhibitor
- ag+, cn- inhibit enzymes cytochrome oxidase (cellular resp) binds to -SH group, breaks disulfide linkages that hold tert. structure o enzyme
- allosteric enzymes have two non-overlapping binding sites; one active, one allosteric site
- regulatory molc behave like REVERSIBLE non competitive inhibitors
- change enzymes shape and function by binding weakly to allosteric site; specific receptor site on enzyme molc remote fr active site
- structure enzyme altered so substrate less likely to bind to active site
explain role control o metabolic pathways by end product inhibition and role o allosteric sites
- metabolic pathways, product o last reaction inhibits enzyme that catalyses first reaction = end product inhibition, allosteric inhibitor
- end product if amount large enough will bind to allost site shutting down pathway preventing creation o more end product
- reversible,when end product lessens,detached enzyme returnes to original shape so active site can bind substrate again
- regulates metabolism according to req o organism
- negative feedback or feedback inhibition, stops or slows chemical reactions inside cell
- e.g. surplus ATP = allosteric reg o one or more pathways involved in cellular resp by binding to phosphofructokinase
- e.g. threonine binds to theronine dehydratase, end product isoleucine inhibits threonine dehydratase
Outline DNA nucleotide structure in terms of sugar (deoxyribose), base and phosphate, draw
- DNA composed o subunits called nucleotides
- deoxyribonucleic acid
- circle phosphate group
- pentagon sugar (deoxyribose)
- rectangle nitrogenous base
Name four bases o DNA
Outline how DNA nucleotides are linked together by covalent bonds into a single strand
A covalent bond forms between the sugar of one nucleotide with a phosphate group and the phosphate group of another nucleotide.
draw 3 rungs of DNA ladder with letters labelled, relative sizes and positions of deoxyribose should be accurate, hydrogen bonds
explain how DNA double helix is formed w/ complementary base pairing and hydrogen bonds
- DNA is made up of two nucleotide strands.
- connected together by covalent bonds within each strand.
- sugar of one nucleotide forms a covalent bond with the phosphate group of another.
- two strands themselves connected by hydrogen bonds.
- hydrogen bonds found between the nitrogen bases of the two strands of nucleotides.
- Adenine forms hydrogen bonds with thymine
- Guanine forms hydrogen bonds with cytosine.
- called complementary base pairing.
- A nucleotide will only pair with another if it is “upside down”, therefore 1 strand runs opposite though parallel
- Bonds between the strands creates a double helix shape that resembles a twisted ladder