Describe the genetic code and its relationship to polypeptides and proteins.

Outline the role of proteins in active and passive transport of molecules through membranes.

Many cell functions, like synthesis of macromolecules and transport, require energy in the form of ATP.  Explain how ATP is generated in animal cells.

Remember, up to TWO “quality of construction” marks per essay.

a. (the genetic code is based on) sets of three nucleotides/triplets of bases called codons;
b. bases include adenine, guanine, cytosine and thymine in DNA / adenine, guanine, cytosine and uracil in RNA; (do not accept ATCG)
c. each codon is code for one amino acid;
d. some codons are (start or) stop codons;
e. DNA is transcribed into mRNA by base-pair matching/complementary base pairing;
f. mRNA is translated into a sequence of amino acids/polypeptide;
g. each gene codes for a polypeptide;
h. polypeptides may be joined/modified to form proteins;

Remember, up to TWO “quality of construction” marks per essay.

a. channel proteins allow diffusion/osmosis/passive transport;
b. large/polar molecules cannot cross the (hydrophobic) membrane freely;
c. facilitated diffusion involves moving molecules through proteins down their concentration gradient/without requiring ATP;
d. aquaporins (specific integral membrane proteins) facilitate the movement of water molecules/osmosis;
e. some proteins (for facilitated diffusion) are specific to molecule/ions;
f. active transport involves moving molecules through proteins against their concentration gradient/requiring ATP;
g. (some) proteins in the membrane are pumps / pumps perform active transport / sodium potassium pump;

Remember, up to TWO “quality of construction” marks per essay.

a. ATP is a form of energy currency/immediately available for use;
b. ATP is generated in cells by cell respiration (from organic compounds);
c. aerobic (cell respiration) requires oxygen;
d. anaerobic (cell respiration) does not require oxygen;
e. glycolysis breaks down glucose into pyruvate;
f. glycolysis occurs in cytoplasm;
g. (by glycolysis) a small amount of ATP is released;
h. ADP changes into ATP with the addition of a phosphate group/phosphoric acid / accept as chemical equation;
i. in mitochondria/aerobic respiration produces large amount of ATP / 38 mols (for the cell, per glucose molecule);
j. oxygen/aerobic respiration is required for mitochondrial production of ATP;
k. in mitochondria/aerobic respiration pyruvate is broken down into carbon dioxide and water;

Many mentioned codons and anticodons, but few explained what they are. Most gained marks from stating that one gene codes for one polypeptide, and that polypeptides can be linked or modified to form proteins.

Many were confused by the differences between channel proteins (passive) and protein pumps (active).

There were several comments about how the students could gain 8 marks on a question about ATP. It was obvious that some students had studied option C, but this should not really have given them an advantage. In fact the students found this question much easier than the teachers thought, scoring well in this section.