Cambridge International A Level Biology Revision Guide

Chapter 12: Energy and respiration
CO 2 glucose O 2
cell surface membrane of cell
mitochondrion
glycolysis
pyruvate
cytoplasm
mitochondrial envelope
intermembrane space
link reaction
inner
membrane
outer
membrane
ATP
ACoA
Krebs
cycle
reduced
NAD
reduced
FAD
matrix
H +
electron
transport
chain
ADP + P i
ATP
oxidative
phosphorylation
crista
H +
H 2 O
Figure 12.11 The sites of the events of respiration in a cell. ACoA = acetyl coenzyme A.
molecule entering the chain produces on average two and a
half molecules of ATP, and each reduced FAD produces one
and a half molecules of ATP. The number of ATP molecules
actually produced varies in different tissues and different
circumstances, largely dependent on how much energy is used
to move substances into and out of the mitochondria.
Hydrogen carrier molecules
NAD is made of two linked nucleotides (Figure 12.12).
Both nucleotides contain ribose. One nucleotide
contains the nitrogenous base adenine. The other has a
nicotinamide ring, which can accept a hydrogen ion and
two electrons, thereby becoming reduced.
NAD + 2H reduced NAD
NAD + + 2H NADH + + H +
A slightly different form of NAD has a phosphate group
instead of the hydrogen on carbon 1 in one of the ribose
rings. This molecule is called NADP (nicotinamide
adenine dinucleotide phosphate) and is used as a hydrogen
carrier molecule in photosynthesis.
FAD (flavin adenine dinucleotide) is similar in
function to NAD and is used in respiration in the Krebs
cycle. FAD is made of one nucleotide containing ribose
and adenine and one with an unusual structure involving
a linear molecule, ribitol, instead of ribose.
O –
nicotinamide ring
O
P
O
O
CH 2
H
NH 2
N
N
H
N N
O – P O CH 2
O
O
H H
H
H
OH
OH OH
Key
replaced by a phosphate group in NADP
site which accepts electrons
Figure 12.12 NAD (nicotinamide adenine dinucleotide). You
do not need to learn the structure of this molecule, but may
like to compare it with the units that make up DNA and RNA.
O
H
OH
N
H
H
H
O
C
NH 2
ribose
adenine
ribose
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