Respiration

Question 1

What is an anabolic reaction?

Answer 1

Chemical reaction in which small molecules are built up into larger ones,using an energy input

Question 2

How do cells continuously regenerate ATP during respiration?

Answer 2

Substrate-level phosphorylation = direct transfer of a phosphate group from a donor molecule to ADP

Chemiosmosis = uses movement of protons across a membrane to drive ATP synthesis

Question 3

What is respiration?

Answer 3

Enzymatic release of energy from organic compounds in living cells, energy stored in ATP the primary energy carrier in all living organisms

Question 4

What are the 2 types of cellular respiration?

Answer 4

Aerobic = requires oxygen
Anaerobic = doesn’t require oxygen

Question 5

What are the 4 main stages of aerobic cellular respiration?

Answer 5

• glycolysis
• link reaction
• Krebs cycle
• oxidative phosphorylation

Question 6

Where does glycolysis occur?

Answer 6

In the cell cytoplasm

Question 7

What are the reactants of glycolysis?

Answer 7

• 1 glucose molecule
• 2 ATP molecules

Question 8

What are the products of glycolysis?

Answer 8

• 4 ATP molecules
• 2 reduced NAD molecules
• 2 pyruvate molecules

Question 9

What is the net energy gain from glycolysis?

Answer 9

• 2 ATP molecules
• 2 reduced NAD molecules

Question 10

Describe what happens at the 4 main stages of glycolysis?

Answer 10

Glucose phosphorylation = 2 ATP molecules donate Pi groups to glucose forming hexose bisphosphate

Lysis = hexose bisphosphate molecule is split into 2 molecules of TP

TP phosphorylation = 2nd Pi group is added to each TP molecule converting them into 2 molecules of triose bisphosphate

Dehydrogenation = H removed from each triose bisphosphate molecule (they are oxidised) used to form 2 NADH, 2 pyruvate and 4 ATP through substrate level phosphorylation

Question 11

What happens after glycolysis is finished?

Answer 11

If O2 is available pyruvate moves through mitochondrial membranes by active transport

Question 12

What are the main mitochondria structures?

Answer 12

Outer membrane = separates contents of mitochondrion from rest of cell

Intermembrane space = space between outer and inner membranes which protons are pumped during oxidative phosphorylation

Inner membrane = contains proteins involved in oxidative phosphorylation

Cristae = folds in inner membrane of mitochondria

Matrix = space within inner membrane, site of link reaction and Krebs cycle

Mitochondrial DNA = codes for some proteins required for mitochondrion to function

Mitochondrial ribosomes = used for protein synthesis within mitochondria

Question 13

What are the adaptions of the mitochondria?

Answer 13

Matrix = contains enzymes needed for link reaction and Krebs cycle

Mitochondrial DNA + ribosomes = allow it to produce proteins e.g enzymes

Cristae = increase inner membrane’s SA so contain more proteins e.g those in ETC and enzymes like ATP synthase

Intermembrane space = small so proton conc gradient between the intermembrane space and mitochondrial matrix builds up quickly

Question 14

What are the reactants of the link reaction?

Answer 14

• pyruvate
• NAD
• coenzyme A

Question 15

What are the products of the link reaction?

Answer 15

• acetyl coenzyme A
• reduced NAD
• CO2

Question 16

Where does the link reaction occur?

Answer 16

Mitochondrial matrix

Question 17

What are the 3 main stages of the link reaction?

Answer 17

• decarboxylation
• pyrite oxiddation
• NAD reduction
• acetyl CoA formation

Question 18

What are the stages of the link reaction?

Answer 18

Pyruvate active transport = pyruvate from glycolysis is actively transported into mitochondrial matrix by specific carrier proteins

Decarboxylation = in mitochondrial matrix each pyruvate molecule is decarboxylated losing one CO2 molecule

CO2 removal = CO2 diffuses out of mitochondria as a waste product

Pyruvate oxidation = 2 H atoms are removed from pyruvate to form a 2C molecule (acetate)

NAD reduction = H atoms used to reduce coenzyme NAD forming NADH (an electron carrier)

Acetyl CoA formation = Acetate binds to CoA forming acetyl CoA

Question 19

What happens to acetyl CoA at the end of the link reaction?

Answer 19

Delivers acetyl group to next stage of aerobic respiration (Krebs cycle)

Question 20

Where does the Krebs cycle take place?

Answer 20

Mitochondrial matrix

Question 21

What does each acetyl CoA produce in the Krebs cycle?

Answer 21

• 2 CO2 (by product)
• 3 NADH
• 1 FADH
• 1 ATP molecule

Question 22

What are the main stages in the Krebs cycle?

Answer 22

1) Acetyl CoA (2C acetate) merges with 4C molecule oxaloacetate creating 6C molecule citrate
2) citrate is decarboxylated releasing 2 CO2 molecules
3) citrate also dehydrogenated (oxidised) releasing H that reduce 3 molecules of NAD and 1 molecule of FAD
4) for or each acetyl CoA entering cycle 1 ATP is synthesised directly via substrate-level phosphorylation
5) oxaloacetate is regenerated for next turn of the cycle

Question 23

What is the role of coenzymes?

Answer 23

Initially act as oxidising agents accepting electrons and protons and becoming reduced themselves

reduced coenzymes later donate those gained electrons to ETC facilitating the transfer of electrons crucial for synthesis of ATP

Question 24

What is the difference between NAD and FAD?

Answer 24

• NAD accepts 1 electron and 1 proton when reduced while FAD accepts 2 protons and 2 electrons when reduced
• NAD participates in all stages of respiration while FAD only accepts protons and electrons in Krebs cycle
• NAD results in synthesis of about 3 ATP molecules while FAD results in synthesis of about 2 ATP molecules

Question 25

What is the importance of the Krebs cycle?

Answer 25

- oxidises and breaks down large nutrients into smaller ones e.g CO2 which can be removed as waste product - generates NADH and FADH carrying protons and electrons into oxidative phosphorylation - continually regenerates 4C molecule to combine with acetyl CoA molecules - provides variety of intermediate compounds required for biosynthesis of essential cellular components e.g fatty acids and amino acids

Question 26

Where does oxidative phosphorylation occur?

Answer 26

Inner mitochondrial membrane of the cristae

Question 27

What are the reactants of oxidative phosphorylation?

Answer 27

- reduced NAD - reduced FAD - O2 - ADP and Pi

Question 28

What are the products of oxidative phosphorylation?

Answer 28

- NAD - FAD - H2O - ATP

Question 29

What are the key stages of oxidative phosphorylation?

Answer 29

1) NADH and FADH release H, transferring protons (H+) and electrons (e-) into mitochondrial matrix 2) High-energy electrons passed to an electron carrier from NADH and FADH 3) electrons passed along series of electron carrier molecules in ETC embedded in inner mitochondrial membrane releasing energy as they are transferred 4) energy used to actively transport protons across inner mitochondrial membrane from mitochondrial matrix into intermembrane space 5) accumulation of protons in intermembrane space sets up a steep electrochemical gradient of protons across inner membrane 6) protons diffuse back into mitochondrial matrix down their electrochemical gradient through ATP synthase 7) releases energy and catalyses synthesis of ATP from ADP and Pi 8) final electron acceptor combining with electrons and protons to form H2O helping maintain proton gradient

Question 30

What is chemiosmosis in aerobic respiration?

Answer 30

Chemiosmosis is diffusion of protons across the partially permeable inner mitochondrial membrane down their electrochemical gradient through ATP synthase channels proton movement releases energy used to synthesise ATP converting energy from electrochemical gradient into chemical energy stored in ATP molecules

Question 31

How many ATP are synthesised in oxidative phosphorylation?

Answer 31

Approximately 30

Question 32

What is the difference between aerobic and anaerobic respiration?

Answer 32

- some steps of aerobic respiration occur within mitochondria, while anaerobic respiration only occurs in cytoplasm - only aerobic respiration includes the link reaction, Krebs cycle and oxidative phosphorylation. - aerobic respiration yields approximately 34 ATP per glucose molecule, while anaerobic respiration yields only 2 ATP per glucose molecule

Question 33

How can organisms be classified based on their oxygen requirements?

Answer 33

Obligate anaerobes = organisms can't survive in presence of oxygen Facultative anaerobes = organisms switch between aerobic and anaerobic respiration depending on O2 availability Obligate aerobes = organisms depend on oxygen to synthesise ATP

Question 34

Why can aerobic respiration not continue after glycolysis without NAD?

Answer 34

Can only continue if NADH produced can be oxidised again If all FAD and NAD are reduced they can't accept any more protons and electrons so oxidative phosphorylation can't occur without O2 as the final electron acceptor

Question 35

What are 2 pathways through which cells undergo anaerobic respiration?

Answer 35

- alcohol fermentation - lactic acid fermentation

Question 36

Describe alcohol fermentation?

Answer 36

1) occurs in yeasts and some plants 2) pyruvate loses a molecule of CO2 and is converted into ethanal 3) ethanal accepts a H from reduced NAD 4) produces ethanol and regenerates NAD 5) ethanol can't be further metabolised so must be removed as waste product

Question 37

Describe lactic acid fermentation?

Answer 37

1) occurs in some animals and bacteria 2) pyruvate accepts H from NADH catalysed by lactate dehydrogenase 3) forms lactic acid and regenerates NAD 4) lactic acid can be oxidised back to pyruvate to generate more ATP or stored as glycogen

Question 38

What are alternative respiratory substrates?

Answer 38

Substances other than glucose that can be oxidised by cells to release energy e.g lipids and proteins

Question 39

How can lipids be used as respiratory substrates?

Answer 39

1) lipids are hydrolysed into glycerol and fatty acids 2) glycerol converted into TP and enters glycolysis pathway 3) fatty acids broken down into 2-C fragments and converted into acetyl coenzyme A entering Krebs cycle

Question 40

How can proteins be used as respiratory substrates?

Answer 40

1) proteins hydrolysed into amino acids 2) amino group removed from amino acids (deamination) 3) 3-C compounds converted into pyruvate while 4 and 5 carbon compounds are converted into intermediates in Krebs cycle

Question 41

What are lipids like as an energy store?

Answer 41

Highest ATP yield providing more than 2x ATP per gram compared to carbs, due to their high proportion of C-H bonds making them ideal for long-term energy storage

Question 42

What are proteins like as an energy store?

Answer 42

Intermediate energy yield offering moderate amount of energy with a diverse role in cellular function, only used for respiration when other sources are low

Question 43

What are carbohydrates like as an energy store?

Answer 43

Least energy per gram but similar to proteins although are primary choice for quick energy due to easy accessibility in metabolic pathways

Question 44

What is the respiratory quotient?

Answer 44

Ratio of volume of CO2 produced to volume of O2 used during respiration

Question 45

How can respiratory quotient be calculated?

Answer 45

RQ = volume of CO2 produced ÷ volume of O2 consumed

Question 46

What are the RQ values of the respiratory substrates?

Answer 46

Carbohydrate = 1 Lipid = 0.7 Protein = 0.9

Question 47

What does the RQ tell you about respiratory substrates?

Answer 47

RQ of more than 1 indicates anaerobic respiration is occurring In plants low RQ values might suggest photosynthesis is occurring as CO2 released during respiration is being used

Question 48

How can we work out the specific substrate being respired?

Answer 48

Lipids and proteins require more O2 for oxidation so RQ values are lower