1 - BIOLOGICAL MOLECULES Flashcards
Give two ways in which the structure of starch is similar to cellulose
- polysaccharides
- contain glycosidic bonds
Give two ways in which the structure of starch is different to cellulose
- Starch contains alpha glucose cellulose contains beta glucose.
- Starch (amylopectin) is branched cellulose is straight
- Starch has no hydrogen bond between molecules
- Starch has no micro or macro fibrils
How are sieve cells adapted for mass transport?
- Few organelles/very little cytoplasm/hollow/thick walls -> so easier/more flow
- Cellulose cell wall strengthens the wall to withstand hydrostatic pressures
- Sieve pores that allow continuous movement of substances
- Energy is provided for active transport from mitochondria in the companion cells.
Describe the structure of proteins
PRIMARY - sequence of amino acids in a polypeptide chain held by peptide bonds
SECONDARY - specific folding of polypeptide chain into alpha helices or beta pleated sheet, folding due to H+ bonds between amino acids
TERTIARY - 3-D folding of alpha helices and beta pleated sheet forming hydrogen, ionic and sulphide bonds
QUATERNARY - multiple polypeptide chains held together by hydrogen ionic and disulphide bonds e.g. haemoglobin
Describe and explain the effect of concentration of competitive inhibitors on
the rate of enzyme-controlled reactions
- as concentration of competitive inhibited increases, rate of reaction decreases
- inhibitor is similar shape to substrate so it competes for active site
- fewer enzyme substrate complexes form
Preventing:
-> increasing substrate concentration reduces the effect of inhibitors
Describe and explain the effect of concentration of
non-competitive inhibitors on the rate of enzyme-controlled reactions
- as concentration of non competitive inhibitors increases, rate of reaction decreases
- competitor binds to site other than active site (allosteric site), usually opposite active site
- changes tertiary structure of enzyme
- so active site no longer complementary to substrate
- fewer enzyme substrate complexes
-> increasing substrate concentration has no effect on the rate of reaction as the change to active site is permanent
Compare and contrast the structure of DNA and RNA
DNA:
- Deoxyribose sugar
- Thymine
- Double stranded
- Longer
RNA:
- Ribose sugar
- Uracil
- Single stranded
- Shorter
Explain Meselson and Stahl’s experiment
- Bacteria grown in a broth containing the heavy (15N) nitrogen isotope
- bacteria replicates and uses nitrogen from the broth to make new DNA nucleotides as nitrogen is in bases
- After some time, the culture of bacteria only contained heavy (15N) nitrogen
- DNA from the 15N culture of bacteria was extracted and spun in a centrifuge
- settled near the bottom of the centrifuge tube, this was compared with the 14N culture which settled at the top
- bacteria containing only 15N DNA was then taken out of the 15N broth and added to a broth containing only the lighter 14N nitrogen
- bacteria left for enough time for one round of DNA replication to occur before their DNA was extracted and spun in a centrifuge
- DNA settled in the middle showing that semi conservative replication had occurred as the band settled in the middle of the tube
Describe the complete digestion of starch by a mammal
- Hydrolysis of glycosidic bonds
- starch hydrolysed to maltose by amylase
- maltose hydrolysed to glucose by maltase in the small intestine
(No digestion occurs in the stomach)
Describe the basic function and structure of starch and glycogen
Starch: energy store in PLANT cells
- polysaccharide of alpha glucose
Amylose - 1,4 glycosidic bonds -> unbranched
Amylopectin - 1,4 and 1,6 glycosidic bonds -> branched
Glycogen: energy store in ANIMAL cells
- polysaccharide of alpha glucose
- 1,4 and 1,6 glycosidic bonds -> branched
Explain how the structures of starch and glycogen relate to their functions
Starch (amylose):
- helical = compact for storage in cell
- large, insoluble = cannot leave cell/cross cell membrane
- insoluble in water = water potential of cell not affected (no osmotic effect)
Glycogen (and starch amylopectin):
- branched = compact for storage in cell
- branched = more ends for faster hydrolysis (to realise glucose for respiration to make ATP for energy release)
- large, insoluble = cannot leave cell/cross cell membrane
- insoluble in water = no osmotic effect
Describe the basic structure and function of cellulose
Provides strength and structural support to plant/algal cell walls
- polysaccharide of beta glucose
- 1,4 glycosidic bonds (straight, unbranched chains)
- chains linked in parallel by hydrogen bonds forming micro fibrils
Explain how the structure of cellulose relates to its function
- every other beta glucose molecule is inverted in a long, straight, unbranched chain
- many hydrogen bonds link parallel strands (crosslinks) to form microfibrils
- hydrogen bonds are strong in high numbers -> provides strength to plant cell walls
Name 2 types of lipid
Triglycerides
Phospholipid
Describe the difference between saturated and unsaturated fatty acids
Saturated - no c=c double bonds, all carbons fully saturated with hydrogen
Unsaturated - one or more c=c double bond in hydrocarbon chain
What is a triglyceride composed of
1 glycerol molecule
3 fatty acid molecules
3 ester bonds
What is a phospholipid composed of
1 glycerol molecule
2 fatty acid molecules
1 phosphate group
Describe how triglycerides form
● 1 glycerol molecule and 3 fatty acids
● Condensation reaction
● Removing 3 water molecules
● Forming 3 ester bonds
Suggest how the properties of ATP make it a suitable immediate source of energy for cells
- releases energy in small amounts
- single reaction (one bond hydrolysed to release energy)
- immediate release of energy
- cannot pass out of cell
Explain 5 properties of water
METABOLITE - many chemical reactions involve water (condensation, hydrolysis, photosynthesis, respiration)
SOLVENT - many substances dissolve in water (allows transport of substances around body)
HIGH SPECIFIC HEAT CAPACITY - requires a lot of energy to change its temperature allows the body to remain a fairly stable temperature)
HIGH LATENT HEAT OF VAPORISATION - high boiling point, takes a lot of energy to change from a liquid to a gas (organisms can use evaporation of water as a method of cooling without loosing too much water
STRONG COHESION BETWEEN WATER MOLECULES - tendency of water molecules to stick together due to hydrogen bonds (makes transport of water easier eg. columns of water in xylem), also creates surface tension allowing small organisms to walk across its surface
Describe the role of inorganic ions
HYDROGEN - maintains pH levels in the body (pH scale is determined by number of H+ ions, more H+ ions = lower pH so more acidic) also affects enzyme rate of reaction as it can cause enzymes to denature
IRON - component of haem group of haemoglobin, allows oxygen to bind for transport as oxyhemoglobin)
SODIUM - involved in co transport of glucose/amino acids into cells, involved in action potentials, affects water potential of cells/osmosis
PHOSPHATE - component of nucleotides, component of ATP allowing energy release, phosphorylates other compounds making them more reactive, hydrophilic part of phospholipids allowing a bilayer to form
Describe the digestion of protein in mammals
Protein digestion begins in the stomach
- endopeptidase hydrolyses peptide bonds within proteins, creating smaller sized protein ‘chunks’ of polypeptides
- partially digested food then moves to the small intestine
- pancreatic juice travels from the pancreas, containing exopeptidase
- exopeptidases hydrolyse peptide bonds at the ends of the polypeptide chains to produce dipeptides
- dipeptidases found in the cell membrane of the epithelial cells hydrolyse dipeptides into amino acids
