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Why do living organisms need energy?

Active transport; endocytosis, exocytosis incl secretion of large molecules from cell; protein synthesis; DNA replication; cell division; movement of flagella, cillia, motor proteins; activation of molecules eg phosphorylation of glucose in glycolysis.


Define a catabolic reaction.

Metabolic reaction in which large molecules are hydrolysed to small molecules.


Define an anabolic reaction.

Metabolic reaction in which larger molecules are synthesised from smaller molecules.


What is the structure of ATP?

Adenine, ribose, three phosphate groups.


Why is ATP a good energy store?

Universal; stable in solution within cells; energy easily released by hydrolysis; energy released in small, manageable amounts.


What are the two types of respiration and when are they used?

Aerobic respiration – in presence of plenty of oxygen.
Anaerobic respiration – in absence of oxygen.


Name the 4 stages of respiration.

Glycolysis, link reaction, Krebs cycle, electron transport chain.


Describe what happens in glycolysis, where it occurs and what is produced.

Glycolysis happens in the cytoplasm of all living organisms.
It does not require oxygen.
Glucose is phosphorylated by two phosphate molecules to make phosphorylated glucose.
Two phosphate molecules came from the hydrolysis of 2 molecules of ATP into ADP and Pi.
This lowers the activation energy so that the following reactions can occur.
Phosphorylating glucose maintains glucose concentration gradient so diffusion continues.
Phosphorylated glucose is split into 2 molecules of triose phosphate.
Triose phosphate is oxidised, NAD reduced to NADH.
4 ATP are regenerated from ADP and Pi, per triose phosphate.
Triose phosphate is converted to pyruvate.
Net yield is: 2 ATP, 2 NADH, 2 pyruvate.


Describe the structure of a mitochondrion.

Rod shaped, cylindrical.
Length: 2.0-5.0μm.
Inner and outer phospholipid membranes separated by intermembrane space.
Inner membrane folded into cristae, embedded with transport proteins and ATP synthase.
Inner membrane encloses matrix - semi rigid, gel like, contains ribosomes, looped mitochondrial DNA and enzymes.


How do the structures of mitochondria support their function?

Matrix: contains enzymes needed for link reaction and Krebs cycle, contains coenzymes NAD and FAD, contains 4C oxaloacetate needed for Krebs cycle, mitochondrial DNA which codes for some mitochondrial enzymes and proteins, mitochondrial ribosomes for protein synthesis.
Outer membrane: phospholipid bilayer similar to that of other membrane bound organelles, contains carrier and transport proteins.
Inner membrane: phospholipid bilayer differs in composition, impermeable to small ions eg H+, folded to provide large surface area for carrier proteins and ATP synthase - the electron transport chain.
Intermembrane space: space between membranes allows for compartmentalisation of ions and intermediates, enables proton concentration gradients to form for chemiosmosis.
Electron transport chain: series of electron carrier proteins embedded in cristae, known as oxio-reductase enzymes, each protein complex contains a non-protein haen cofactor, three of the four complexes use energy from electrons to pump protons from matrix to intermembrane space, proton gradient forms, protons flow through ATP synthase to synthesis ATP.
ATP synthase: stalked enzyme embedded in cristae, acts as proton channel for proton flow.


Describe what happens in the link reaction, where it occurs and what is produced.

The link reaction only occurs in the presence of oxygen.
The link reaction occurs between the cytoplasm and the mitochondria.
The pyruvate from glycolysis is actively transported into the mitochondria via a pyruvate H+ symport protein
pyruvate is decarboxylated, CO is removed as carbon dioxide.
Pyruvate is dehydrogenated, H is used to reduce NAD the remaining 2C acetyl group combines with coenzyme A to make acetylcoenzyme A.
Acetyl group carried into matrix to be used in Krebs cycle.


What is the coenzyme involved in the link reaction?

Coenzyme A, CoA.


Describe what happens in the Krebs cycle (citrus acid cycle), where it occurs and what is produced.

The Krebs cycle happens in the mitochondrial matrix in a series of enzyme catalysed reactions.
Acetylcoenzyme A is released from the 2C acetate.
CoA is recycled back to cytoplasm.
2C acetate combines with a 4 carbon molecule, oxaloacetate, to make a 6 carbon molecule, citrate.
Citrate is decarboxylated, releasing carbon dioxide, and it is dehydrogenated, hydrogen used to reduce NAD.
5C molecule is decarboxylated and dehydrogenated to produce one molecule of carbon dioxide and one molecule of NADH.
This gives a 4C molecule which briefly combines with CoA leading to the phosphorylation of ADP to give ATP by substrate level phosphorylation. The 4C molecule is dehydrogenated to form FADH2.
The 4C molecule is isomerized and dehydrogenated to regenerate oxaloacetate.
For every glucose molecule there are two turns of the Krebs cycle.
Net yield: Two molecules of carbon dioxide are released; three NADs are reduced to NADH; one FAD is reduced to FADH2; one molecule of ATP is made from ADP and Pi by substrate level phosphorylation.


State the product made per glucose molecule and how much is made in the link reaction and Krebs cycle.

NADH (redNAD): Link reaction: 2 Krebs cycle: 6
FADH (redFAD): Link reaction: 0 Krebs cycle: 2
Carbon dioxide: Link reaction: 2 Krebs cycle: 4
ATP: Link reaction: 0 Kreb cycle: 2


State the other respiratory substrates that can be respired aerobically.

Fatty acids - broken down into acetate, enter Krebs cycle via CoA.
Glycerol - converted into pyruvate, into link reaction then Krebs cycle.
Amino acids - deamination, remaining carbon skeleton enters Krebs or is converted to pyruvate and enters link reaction.


What is chemiosmosis?

Flow of protons, down their concentration gradient, across a membrane, through a proton channel in ATPsynthase.


What is oxidative phosphorylation?

Formation of ATP in the presence of oxygen using energy released from the electron transport chain.


What is the total yield of ATP during aerobic respiration and where does it occur?

Glycolysis: 2
The link reaction: 0
The Krebs cycle: 2
Oxidative phosphorylation: 28
Total: 32


Describe what happens in the electron transport chain (chemiosmosis), where it occurs and what is produced.

NADH and FADH2 are oxidised and donate electrons from the hydrogen atoms to the first protein in the electron transport chain (complex I for NADH) (complex II for FADH2) Protons from hydrogen atoms in solution in matrix.
Electrons are passed down the electron transport chain through a series of oxidation – reduction reactions; carrier proteins contain iron ions.
As electrons pass some energy used to actively pump protons into the intermembrane space.
Proton gradient is established.
Protons move back into matrix through ATP synthase, chemiosmosis.
Energy used to condense ADP + Pi → ATP/ phosphorylation of ADP to ATP.
Oxygen used as final electron acceptor in the electron transport chain (combines with the electrons and protons).
Water is formed.


Why is the theoretical yield of 32 ATP/ molecule of glucose rarely met?

Outer mitochondrial membrane partially permeable to protons.
ATP used to actively transport pyruvate into mitochondria.
ATP used to transfer NADH from cytoplasm into mitochondria.


What happens during respiration if oxygen is absent?

No final electron acceptor.
Protons and electrons not able to combine with oxygen to form water.
Proton concentration in matrix increases, proton gradient across inter membrane space decrease.
Oxidative phosphorylation stops.
NADH and FADH cannot be reduced.
Krebs cycle and link reaction stop.
Feedback inhibition.


Describe what happens in anaerobic respiration in animals, where it occurs and what is produced.

Lactate fermentation pathway.
Happens in the cytoplasm.
Pyruvate accepts hydrogen atoms from NADH.
Pyruvate reduced to form lactate.
NADH reoxidised to NAD.
Glycolysis pathway continues.


What happens to the lactate produced during anaerobic respiration?

Only in the presence of oxygen.
Lactate is converted back to pyruvate and enters link reaction and Krebs cycle.
Or recycled to glucose and glycogen.


Describe what happens in anaerobic respiration in yeast (fermentation) (and some other microorganisms) and what is produced.

Pyruvate from glycolysis decarboxylated by pyruvate decarboxylase to give ethanal.
Pyruvate decarboxylase has a bound coenzyme, thiamine diphosphate.
Ethanal reduced by ethanol dehydrogenase to form ethanol.
NADH is reoxidised and made available to accept more H ions from triose phosphate so glycolysis can continue.
Ethanol and NAD are made as a result of this.


Why does anaerobic respiration occur if no ATP is synthesised?

Allows reoxidation of NAD so glycolysis can continue.
Glycolysis yields 2 ATP.
Low yield but many molecules of glucose can be split/ minute.
Yield is 1/15th that of aerobic respiration.


Yeast is a facultative anaerobe, what does this mean?

If oxygen is available, yeast follows the aerobic pathway.
If oxygen concentrations are low, yeast follows the ethanol fermentation pathway.


Describe how to use a respirometer to measure respiration rate.

Place an equal volume of sodium hydroxide solution in each test tube - absorbs carbon dioxide.
Record the mass / volume of the living organism being used, and record an equivalent mass / volume of glass beads - this ensures the same volume of gases in each test tube.
Place the organism in one tube and the beads in the other, suspended above the sodium hydroxide to prevent the death or injury to the organism.
Use the syringe to calibrate the fluid in the manometer / U tube - make the fluid level in each arm of the tube and mark this level so you know where the fluid started.
Close the valve on each test tube - to ensure no gases enter / leave the respirometer.
As the organism respires, oxygen is removed from the test tube and carbon dioxide is released into the test tube. The carbon dioxide is absorbed by the soda lime -
this reduces the volume of gas in the tube containing the organism. A reduction in volume leads to a reduction in air pressure. The air pressure in the tube containing the glass beads is greater than the air pressure in the tube containing the organism.
Air moves down the pressure gradient from the glass bead tube to the tube containing the organism, pushing the fluid up the arm of the tube, towards the organism.
Start the timer and leave investigation to run - suggest a time, e.g. 120s. Record distance moved, mm.
Calculate rate-distance/time =rate mm/s OR use the syringe to adjust the fluid back to the starting point and record the volume of gas needed. Use this volume to calculate rate of respiration -ml/s.


What is a respiratory substrate?

An organic substance that can be oxidised by respiration. Energy released is used to synthesise ATP.


Name three respiratory substrates.

Carbohydrates containing alpha glucose; lipids; proteins.


Why can’t we respire beta glucose?

Enzymes are not available for its digestion so it doesn’t enter body cells.