OCR A Level Biology Respiration

What type of molecule is cyanide?

What type of molecule is cyanide?

Small and non-polar, so can pass through membranes

What are the three categories that organisms can be grouped into based on their dependence on oxygen?

1. Obligate anaerobe
2. Facultative anaerobe
3.Obligate aerobe

What are obligate anaerobes?

Organisms which cannot survive in the presence of oxygen.

What type of organism are obligate anaerobes?

Mostly prokaryotes, some fungi

What are facultative anaerobes?

Organisms which synthesise ATP by aerobic respiration if oxygen is present, but can switch to anaerobic respiration if necessary

What is an example of a facultative anaerobe?

Yeast

What are obligate aerobes?

Can only synthesise ATP in the presence of oxygen

Why are humans obligate aerobes even though some cells in them can be facultative anaerobes?

The compounds produced by anaerobic respiration in those cells must be broken down by oxygen, so the organism as a whole is an obligate aerobe

What type of cell does lactate fermentation occur in?

Animal cells

Why is fermentation of pyruvate necessary in anaerobic respiration?

To ensure that NAD can cycle between its reduced and oxidised states, so that glycolysis can continue occurring

Briefly summarise the reactions of glycolysis

1. Two Pi groups from ATP attach to glucose to form hexose bisphosphate
2. Hexose bisphosphate breaks down into 2 triose phosphate molecules because it is unstable
3. Each triose phosphate has a free Pi group attach to form triose bisphosphate
4. Both Pi are removed by ADP to form ATP, and a H atom dissociates and forms NADH. Pyruvate is what is left behind

What is glycolysis an example of?

Substrate level phosphorylation

What is the net gain of glycolysis?

2 ATP, 2 NADH, 2 pyruvate

What is the function of cristae?

Increase the surface area of the inner mitochondrial membrane for oxidative phosphorylation

What is the function of the outer mitochondrial membrane?

Separates the contents of the mitochondrion from the rest of the cell to allow maintenance of conditions perfect for aerobic respiration

What does the matrix contain?

Enzymes for the Krebs cycle and Link Reaction, mitochondrial DNA

What does the inner mitochondrial membrane contain?

Electron transport chains and ATP synthase

What is an adaptation of the intermembrane space in mitochondria?

Is small so allows a quick buildup of protons when they are pumped in for chemiosmosis

How does pyruvate enter the mitochondria?

Via active transport

What is another name for the Link Reaction?

Oxidative decarboxylation

Briefly summarise what happens in the Link Reaction?

CO2 is removed from pyruvate. This forms a H+ ion which reduces NAD, and leaves an acetyl group which combines with CoA to form acetyl CoA

Where does the Krebs Cycle occur?

The matrix

What is the Krebs Cycle also known as?

The Citric Acid Cycle

What are the products of one turn of the Krebs cycle (i.e. after inputting one acetyl CoA)?

2 CO2, 3 NADH, 1 FADH and 1 ATP

What are the products of oxidative phosphorylation for one molecule of glucose?

10 NAD, 2 FAD, 6 H2O, 28 ATP

How does oxidative phosphorylation produce ATP?

Hydrogen atoms on reduced coenzymes dissociate to form H+ ions and high energy electrons. These high energy electrons enter an electron transport chain, with the energy thus provided used to produce ATP via chemiosmosis.

Where does oxidative phosphorylation occur?

The inner mitochondrial membrane and intermembrane space

How many electron carriers are involved in the electron transport chain of oxidative phosphorylation?

3

How is water formed during oxidative phosphorylation?

1/2 an O2 molecule and 2 H+ ions act as electron acceptors for two low energy electrons from the electron transport chain

How many ATP molecule can one NADH molecule synthesise?

2.5

How many ATP molecule can one FADH molecule synthesise?

1.5

How many ATP molecules are in theory produced by aerobic respiration and why is this not the true net gain?

32, but is lower in practice as active transport needed to transport pyruvate into the mitochondria

How does cyanide kill you?

It readily binds to a haem group in the last electron transport chain of oxidative phosphorylation, so electrons cannot bind and oxidative phosphorylation (and therefore ATP production) are inhibited

Why does cyanide inhibit the Krebs Cycle and Link Reaction?

Lots of NADH and FADH would stockpile as they couldn't be oxidised, so there wouldn't be enough NAD and FAD.

What is an example of a class of obligate aerobes?

Mammals

What type of cells does alcoholic fermentation occur in?

Yeast and some plant root cells

What are the 4 stages of aerobic respiration?

1. Glycolysis
2. Link Reaction
3. Krebs Cycle
4. Oxidative Phosphorylation

What is the primary substrate used in respiration?

Glucose

What are the 3 coenzymes used in respiration?

1. CoA (Coenzyme A)
2. NAD (Nicotine Adenine Dinucleotide)
3. FAD (Flavine Adenine Dinucleotide)

What stage of respiration uses reduced coenzymes?

Oxidative phosphorylation

What is NAD derived from?

Vitamin B3

What is FAD derived from?

Vitamin B2

What is CoA derived from?

Vitamin B5

Where does glycolysis occur?

In the cytosol

What are the three products of glycolysis?

1. Pyruvate
2. ATP
3. NADH

What is substrate level phosphorylation?

The formation of ATP without using electron transport chains

Where does lactate oxidation occur in humans?

The liver

What are two reasons that anaerobic respiration is not sustainable in mammals?

1. It does not produce enough ATP
2. Lactate is a toxin (due to the pH change it causes which affects enzymes) and needs oxygen to break it down

What is the word equation for anaerobic respiration involving lactate fermentation?

Glucose ----> Lactic Acid + Water

What happens to NADH during fermentation?

It is oxidised to NAD, which is one of the molecules necessary for glycolysis

Is lactate fermentation reversible?

Yes

Is alcoholic fermentation reversible?

No

What are the two stages of anaerobic respiration?

1. Glycolysis
2. Fermentation

Which enzyme catalyses the conversion of pyruvate to ethanal?

Pyruvate decarboxylase

What is pyruvate converted to in alcoholic fermentation? (2 steps)

First ethanal, then ethanol

What happens to ethanal in alcoholic fermentation?

It accepts a H atom from NADH, forming ethanol and NAD.

Why can't ethanolic fermentation continue indefinitely?

Due to the buildup of ethanol, which is a toxin as it damages plasma membranes and kills yeast if concentrations reach above about 15%

How is respiratory quotient calculated?

CO2 produced/O2 consumed

What can respiratory quotient be measured using?

A respirometer

What is the approximate respiratory quotient of carbohydrates?

1.0

What is the approximate respiratory quotient of proteins?

0.9

What is the approximate respiratory quotient of lipids?

0.7

Why is the RQ of lipids lower than that of glucose?

Because of the increased number of C-H bonds in lipids

Why can lipids produce lots more ATP than carbohydrates per molecule?

Because the long fatty acid chains have lots of C-H bonds and can lead to the formation of lots of acetyl CoA, and in turn lots of ATP

How are lipids respired?

Lipids are hydrolysed into fatty acids and glycerol. Glycerol can be converted to pyruvate, whilst the fatty acids can be converted to many CoA molecules

How are proteins respired?

They are metabolised into amino acids, then deaminated, and can then enter the respiratory pathway (usually as pyruvate)

Why are proteins usually only used as a respiratory substrate as a last resort?

They are less efficient than other substrates,this reduces the number of amino acids available to synthesise proteins, damages muscles and causes urea buildup

What is RQ during anaerobic respiration?

Above 1, although this is difficult to measure

What is human RQ during normal activity?

0.8-0.9

What does the human RQ during normal activity show?

Shows that both lipids and carbohydrates are being used