Respiration including Glycolysis and Link Reaction

Respiration

Energy cannot be created nor destroyed but san be converted from one form to another.

It exists as potential (stored) energy and kinetic energy.

a) All living organisms need energy to run their biological processes. These are collectively called metabolism.

Anabolic= build up large molecules, catabolic= large molecule → small molecules
some energy from catabolic reactions is heat which is useful as metabolic reactions are controlled by enzymes which need a suitable temp.
These metabolic processes need energy:

Active transport- moving ions across membrane against conc. gradient.

Secretion- large molecules made in some cells exported by exocytosis.

Endocytosis- bulk movement of large molecules into cells

Anabolism examples- smaller molecules → large e.g. proteins AA, steroids cholesterol, cellulose from B-glucose.

Replication of DNA & synthesis of organelles before a cell divides

Movement e.g. flagella, cilia and muscle contraction

Activation of chemicals- glucose is phosphorylated at start of respiration so more unstable and can be broken down to release energy

b) The hydrolysis of ATP is coupled with synthesis reactions e.g. DNA replication or protein synthesis as these require energy. The energy released from ATP hydrolysis is the immediate source of energy for these biological processes.

c) ...

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Endocytosis- bulk movement of large molecules into cells

Anabolism examples- smaller molecules → large e.g. proteins AA, steroids cholesterol, cellulose from B-glucose.

Replication of DNA & synthesis of organelles before a cell divides

Movement e.g. flagella, cilia and muscle contraction

Activation of chemicals- glucose is phosphorylated at start of respiration so more unstable and can be broken down to release energy

c) Adenosine= 0 phosphate groups
Adenosine Monophosphate (AMP) = 1 PG
Adenosine Diphosphate (ADP) = 2 PG
Adenosine Triphosphate (ATP) = 3 PG

Stages of Respiration:
1. Glycosis (cytoplasm) can take place in aerobic & anaerobic conditions. Glucose (6C sugar) broken into 2 molecules of pyruvate (3C).

2. The link reaction (matrix of mitochondria). Pyruvate is dehydrogenated (H removed) and decarboxylated and converted to acetate.
3. Krebs cycle (matrix of mitochondria) acetate is decarboxylated and dehydrogenated.
4. Oxidative Phosphorylation (cristae of mitochondria) ADP is phosphorylated to ATP.

The last three stages will only take place under aerobic conditions. Under anaerobic condition, pyruvate is converted to either ethanol or lactate.

f) Stages of Glycosis (cytoplasm)

Stage one- phosphorylation

Glucose is phosphorylated by adding 2 phosphates from 2 molecules of ATP.
This creates 1 molecule of hexose bisphosphate and 2 molecules of ADP.
Then, hexose bisphosphate is split up into 2 molecules triose phosphate.

Stage two- oxidation

Triose phosphate is oxidised (loses hydrogen), forming 2 molecules of pyruvate.
NAD collects the H+ forming 2 reduced NAD.
4 ATP are produced put 2 are used in stage one, so there is a net gain of 2 ATP.

The 2 molecules of reduced NAD go to the last Stage (oxidative phosphorylation). The 2 pyruvate molecules are actively transported into the matrix of the mitochondria for the link reaction.

Mitochondria are adapted to their function in the following ways:

Inner membrane folded into cristae hence increasing membrane’s SA to maximise respiration.
Lots of ATP synthase molecules to produce lots of ATP in the final stage of respiration.
Matrix contains all reactants and enzymes needed for the Krebs cycle.

i) j) link reaction takes place in the matrix of mitochondria.

1) Pyruvate (3C) is decarboxylated; 1C atom removed from pyruvate in the form of CO2

2) NAD is reduced; it collects H from pyruvate, changing pyruvate into acetate.

3) Acetate (2C) is combined with coenzyme A (CoA) to form acetyl CoA (2C).

4) No ATP is produced in this reaction.

The link reaction occurs for every glucose molecule, so for each g molecule:
2 molecules of acetyl CoA go into Krebs cycle. 2 CO2 molecules released as a waste product of respiration. 2 molecules of NAD formed and go to last stage (OP)

Peer Reviews

Here's what a star student thought of this essay

skatealexia

19th of Aug 2012

Quality of writing

Simple spelling mistakes made by errors in proof-reading. Otherwise, grammar, spelling and punctuation all to a good level. The tone of the piece is correct, but the text is in a format which can be quite hard to read so a simpler font should be used. The candidate splits the work into sections but should use clear subheadings between pieces.

Level of analysis

The definition and the image which are provided do not really add to the essay and explanation of respiration. The candidate would have been better providing equations which they could have then explained a bit better rather than images which are quite subjective in definition. The candidate gives a very long winded definition of anabolism and catabolism without linking it to respiration until the end, and they should have linked earlier to show a direct focus to the question. The different reactions of respiration are explained well and they are broken down into stages and related to the structure of the mitochondria. However, images would have made the stages clearer, and deeper detail in the stages would have showed a deeper understanding and research of the topic.

Response to question

The candidate does this essay well. They relate to the ocr objectives on respiration well and show the different stages of respiration. They go into relatively good detail, although the text could be a bit more focused near the beginning.

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