carbohydrates and lipids

State the type of reaction which converts excess monosaccharides to polysaccharides (1)

condensation/dehydration/synthesis/anabolic/

anabolism ✔

Explain how a polypeptide chain is synthesized in a eukaryotic cell (7). - hint no transcription

a. translation occurs on ribosomes ✔

b. tRNA-activating enzymes attach amino acids to tRNAs ✔

c. small and large ribosome units assemble on mRNA
OR
translation/polypeptide synthesis starts at a start codon ✔

d. each tRNA arriving at the ribosome binds to the A site ✔

e. anticodon «on tRNA» binds to codon «on mRNA» ✔

f. according to complementary base pairing/A with U and G with C ✔

g. ribosome moves along the mRNA / mRNA moves over ribosome ✔

h. t-RNA shifts from the A site to P site/from the P to the E site ✔

i. peptide bond between amino acids «on tRNAs at A and P sites» ✔

j. tRNA released from ribosome at E site ✔

k. cycle repeats with other tRNAs / polypeptide grows as tRNAs bring more amino acids ✔

l. until stop codon on mRNA is reached ✔

m. components are disassembled / polypeptide leaves the ribosome ✔

Broad beans are rich in starch and cellulose. Compare and contrast the structure of starch and cellulose (2)

a. both polymers of glucose molecules / polysaccharides
OR
both form 1,4 glycosidic bond ✔

b. starch is formed by alpha glucose while cellulose is formed by beta glucose
OR
in starch C1 hydroxyl groups are found in same plane while in cellulose on different planes
OR
in cellulose, alternatively the beta glucose needs to be placed upside-down in order to have C1 hydroxyl groups on the same plane
OR
two types of starch (amylose and amylopectin) but one type of cellulose ✔

Once the germinated bean grows above the ground, state the process used by the bean in the production of starch (1)

photosynthesis

Describe the structure of starch (5)

a. starch is a carbohydrate ✔

b. starch is formed by carbon, hydrogen and oxygen ✔

c. it is a polymer/chain/polysaccharide ✔

d. formed from monosaccharides/simple sugars/glucose ✔

e. linked together by condensation/dehydration ✔

f. consists of amylose and amylopectin ✔

g. amylose is a long chain/unbranched ✔

h. amylopectin is branched ✔

Outline how the structure of cellulose makes it suitable as a component of cell walls (2)

a. chains of glucose/1-4 glycosidic linkages/covalent bonding between glucose ✔

b. beta glucose so alternating orientation of glucose units
OR
beta glucose forms straight chains ✔

c. forms microfibrils/long and thin/thin fibres/parallel bundles of cellulose molecules
OR
hydrogen bonding/cross linkage between cellulose molecules holds them together ✔

d. high tensile strength/rigid/doesn’t stretch so provides support/allows turgidity ✔

Outline a function of cholesterol in cell membranes (1)

reduces fluidity of membrane / reduces permeability of membrane (to some molecules);

State the property of amphipathic phospholipids that enables them to form a bilayer (1)

have both a hydrophilic and a hydrophobic region
OR
have both a polar and a non-polar region ✔