Essay
DISTINCTION - Unit 10 Biological Molecules and Metabolic Pathways - Assignment B
- Module
- Unit 10
- Institution
- PEARSON (PEARSON)
the effect of activity on respiration in humans and factors that can affect respiratory pathways
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UNIT 10 ASSIGNMENT BB.P2 - explain the stages involved in human respiratory pathway
B.P3 - carry out investigations involving the effect of activity on respiration in humans
B.P4 - describe factors that can affect respiration
B.M2 - analyse primary and secondary data to explain the effect of activity on respiration
B.M3 - explain the harmful effects of factors on respiration
B.D2 - evaluate the effect of harmful substances on the efficiency of respiration
The are four stages in aerobic respiration known as glycolysis, the link reaction, the Krebs
cycle, and oxidative phosphorylation. The first three stages are reactions. The products of
these reactions are used in the final stage to produce loads of ATP.
STAGE 1 – GLYCOLYSIS – makes pyruvates from glucose
Glycolysis involves splitting one molecule of glucose (with6 carbons) into two smaller
molecules of pyruvate (each has 3 carbons). The process happens in the cytoplasm. It is the
first stage of both aerobic and anaerobic respiration and does not need oxygen to take place
making it aerobic.
There are two stages in glycolysis called phosphorylation and oxidation
Glycolysis is the process of converting one molecule of glucose (with six carbons) into
two smaller pyruvate molecules (each has 3 carbons). The procedure takes place in the
cytoplasm. It is the first stage of both aerobic and anaerobic respiration, and it is aerobic
because it does not require oxygen.
Phosphorylation and oxidation are the two stages of glycolysis.
1. Phosphorylation – glucose is phosphorylated by the addition of two phosphates from
two ATP molecules. One molecule of hexose bisphosphate and two molecules of ADP
are produced. Hexose bisphosphate is then broken down into two molecules of triose
phosphate.
2. Oxidation: When triose phosphate loses hydrogen, it forms two molecules of
pyruvate. The hydrogen ions are collected by NAD, which results in the formation of 2
reduced NAD. There are four ATP molecules produced, but two were used up in stage
one, resulting in a net gain of two ATP molecules.
STAGE 2 – THE LINK REACTION – converts pyruvates to acetyl coenzyme A
The link reaction takes place in the mitochondrial matrix.
Pyruvate is decarboxylated, which means a carbon from the pyruvate is removed in
the form of CO2.
NAD is converted to NADH by collecting hydrogen from pyruvate and converting it
to acetate.
Acetate is combined with coenzyme A to form acetyl coenzyme A
No ATP is produced in this reaction
Every glucose molecule undergoes the link reaction twice. For every glucose molecule that
enters glycolysis, two pyruvate molecules are produced. This means that for every glucose
molecule, the link reaction and the third stage occur twice.
(Fielding and Anderson, n.d.)
, STAGE 3 – THE KREBS CYCLE -produces reduced coenzymes and ATP
The Krebs cycle is a series of oxidation-reduction reactions that occur in the mitochondria's
matrix. Because the cycle occurs once for each pyruvate molecule, it occurs twice for each
glucose molecule.
1. 1. Citrate is formed when the acetyl group from acetyl coenzyme A binds with
oxaloacetate. Citrate synthase catalyses this reaction. Coenzyme A returns to the link
reaction to be used again
2. 2. A 6C citrate molecule is transformed into a 5C citrate molecule. When CO 2 is
removed, decarboxylation occurs. From NAD, hydrogen is used to produce reduced
NAD.
3. The 5C molecule is converted into a 4C molecule Decarboxylation and
dehydrogenation occur, producing one reduced FAD molecule and two reduced NAD
molecules. The direct transfer of a phosphate group from an intermediate
compound to ADP produces ATP. Substrate-level phosphorylation occurs when a
phosphate group is transferred directly from one molecule to another. Oxaloacetate
has now been formed from citrate.
4. (Fielding and Anderson, n.d.)
STAGE 4 – OXIDATIVE PHOSPHORYLATION AND THE ELECTRON TRANSPORT CHAIN – makes
lots of ATP
Oxidative phosphorylation is the process where the energy carried by electrons from
reduced coenzymes is used to make ATP. It takes place in the inner mitochondrial
membrane
Alcoholic fermentation and lactate fermentation are two types of anaerobic respiration.
Anaerobic respiration occurs in the cytoplasm and does not require oxygen. They both types
begin with glycolysis, but the organisms in which they occur and what happens to the
pyruvate differ.
1. Lactate fermentation – occurs in mammals and produces lactase
Reduced NAD from glycolysis transfers hydrogen to pyruvate to form lactate
and NAD
NAD Can then be reused in glycolysis
NAD is regenerated when lactate is produced. NAD is required for glycolysis to occur. This
means that glycolysis can continue even if there isn't enough oxygen present, allowing a
small amount of ATP to be produced to keep some biological processes functioning. For
short periods of time, our cell can tolerate a high level of lactate. However, too much lactate
is toxic and is excreted into the bloodstream by the cells. In a process known as
gluconeogenesis, the liver absorbs lactate from the bloodstream and converts it back to
glucose.
2. Alcoholic fermentation – occurs in yeast cells and produces ethanol
Co2 is removed from pyruvate to form ethanol
Reduced NAD transfers hydrogen to ethanol to form ethanol and NAD
NAD can then be reused in glycolysis
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