Unit 5 - Energy Transfers in & b/w Organisms

Question 1

what does respiration produce?

Answer 1

ATP

Question 2

what is the structure of atp?

Answer 2

adenine base
ribose
3 phosphate groups

Question 3

how is atp useful in biological processes?

Answer 3

releases energy in small manageable amounts
one step hydrolysis so immediate energy compound
can phosphorylate substances to make them more reactive
can be reformed
small & soluble so easily transported around cell
cannot pass out of cell

Question 4

by what 2 processes is atp formed?

Answer 4

1. substrate-level phosphorylation
   phosphate group is transferred by an enzyme from substrate onto ADP molecule
2. chemiosmosis
   involves the diffusion of protons down electrochemical gradient across ppm
   this releases energy needed by ATP synthase to combine ADP + Pi
   only in aerobic respiration

Question 5

what does chemiosmosis require to work?

Answer 5

specialised membrane containing specific proteins:
- electron transport chain including e- carriers/proton pump proteins
- ATP synthase

source of excited/high energy e-s to be passed along etc

final e- acceptor to enable redox reactions in etc to happen

source of protons (from NADH)

Question 6

what is glycolysis?

Answer 6

the first stage anaerobic and aerobic respiration that occurs in the cytoplasm & is an anaerobic process

Question 7

what stages does glycolysis involve?

Answer 7

phosphorylation of glucose to glucose phosphate (6C) using ATP
splitting of phosphorylated glucose into triose phosphate (3C)
oxidation of triose phosphate to pyruvate (3C) with a net gain of ATP & reduced NAD

Question 8

what happens in glycolysis in anaerobic respiration?

Answer 8

if respiration is only anaerobic, pyruvate is converted to ethanol or lactate
reduced NAD is oxidised
oxidised NAD can be used in further glycolysis, producing ATP

Question 9

what happens after glycolysis in aerobic respiration?

Answer 9

if respiration is aerobic, pyruvate from glycolysis enters the mitochondrial matrix by active transport
then link reaction

Question 10

what stages does the link reaction involve?

Answer 10

1. pyruvate from glycolysis enters the mitochondrial matrix by active transport
2. pyruvate is oxidised to acetate, producing reduced NAD
3. acetate combines with coenzyme A to produce acetylcoenzyme A
4. no atp produced

happens twice so products are 2x

Question 11

overview of Krebs cycle

Answer 11

in a series of oxidation-reduction reactions, the Krebs cycle generates reduced coenzymes and ATP by substrate-level phosphorylation, and carbon dioxide is lost

Question 12

what stages does the Krebs cycle involve?

Answer 12

series of oxidation-reduction reactions in the matrix
1. 2C acetylcoenzyme A from link reaction combines with 4C molecule to produce 6C molecule
2. 6C molecule loses CO2 & hydrogen to form a 4C molecule & single ATP molecule by substrate-level phosphorylation
3. 4C molecule combines with new acetylecoenzyme A to repeat cycle
4. NAD & FAD are reduced in the Krebs cycle too

cycle happens twice bc 2 pyruvate molecules so 2 acetylecoenzyme A molecules

Question 13

define oxidative phosphorylation

Answer 13

the mechanism by which some of the energy in e-s in H atoms carried by reduced NAD & reduced FAD is conserved in the formation of ATP

Question 14

describe the process of oxidative phosphorylation

Answer 14

1. H atoms are released from reduced NAD & reduced FAD as they are oxidised to NAD & FAD. H atoms split into H+ & e-
2. e-s move along the electron transport chain made up of e- carrier proteins in a series of oxidation-reduction reactions, releasing energy at each carrier
3. this energy is used by e- carrier proteins to pump protons from mitochondrial matric into intermembrane space
4. conc. of protons in intermembrane space is greater than in matrix, forming electrochemical gradient
5. protons diffuse down electrochemical gradient through ATP synthase embedded in the inner mitochondrial membrane. this synthesises ATP from ADP & Pi
6. the diffusion of H+ ions across membrane is called chemiosmosis
7. at the end of the etc, the e-s & protons combine with an O2 molecule to form H2O. the O2 molecule is the final electron acceptor

Question 15

what are other respiratory substrates?

Answer 15

lipids
amino acids
which enters the Krebs cycle

Question 16

application: what is the effect of cyanide on the processes of respiration?

Answer 16

prevents transfer of e-s from e- carrier to O2 molecule
–> prevents movement of e-s down etc
–> prevents pumping of protons
–> no electrochemical gradient & no diffusion of H+ through ATPsynthase
–> no ATP produced by oxidative phosphorylation
–> no aerobic respiration
so death of cells that rely on aerobic respiration e.g. cardiac muscles & neurones

Question 17

application: what is the effect of uncoupling proteins on the processes of respiration?

Answer 17

protein channel inserted into inner mitochondrial membrane
gives alternative routes for H+ to diffuse from intermembrane space into matrix not through ATP synthase
this releases heat energy
(common in mitochondria in adipose fat in newborns)

Question 18

application: what is the effect of DNP on the processes of respiration?

Answer 18

gives alternative routes for H+ to diffuse from intermembrane space into matrix not through ATP synthase
this releases heat energy

Question 19

what happens in respiration when oxygen is removed?

Answer 19

etc does not function bc no final electron acceptor
reduced NAD & reduced FAD accumulate bc they cannot release their H atoms at atc to become oxidised
Krebs cycle stops because less NAD or FAD available to transport H
link reaction stops bc no 4C molecule is regenerated so acetylcoenzyme A cannot enter Krebs cycle

only glycolysis can continue, producing 2 ATP molecules

Question 20

describe lactate fermentation in anaerobic respiration

Answer 20

commonly happens in skeletal muscles during exercise when O2 demand exceeds O2 supply

pyruvate is reduced to lactate (lactic acid)
reduced NAD is oxidised
oxidised NAD can be used in further glycolysis, producing ATP

Question 21

what is the problem with lactate & how is it removed?

Answer 21

lactate is acidic & toxic as it can denature enzymes & proteins involved in muscle contraction
lactate is transported to liver where it is oxidised to pyruvate & respired aerobically or converted back into glucose & stored as glycogen

Question 22

describe ethanol fermentation in anaerobic respiration

Answer 22

pyruvate is decarboxylated (CO2 lost) & reduced to ethanol
reduced NAD is oxidised
oxidised NAD can be used in further glycolysis, producing ATP

Question 23

what is the use of ethanol fermentation?

Answer 23

ethanol used in brewing
CO2 used to make bread rise

Question 24

describe a method to investigate the effect of temperature on the rate of respiration of yeast

Answer 24

1. put known conc. & col. of glucose into test tube & add yeast & buffer solution
2. put known vol. of the yeast & glucose solution to three different test tubes. place the test tubes in the 35°C water bath. leave them in there for 10 minutes so the solution temp. equilibrates
3. add methylene blue indicator, using the pipette, to each test tube and start the stopwatch. shake the test tube for 10 seconds then place it back in the water bath.
4. record the time taken for the methylene blue to turn colourless in each test tube
5. repeat the experiment using temperatures 20°C, 30°C, 40°C, 50°C, 60°C and 70°C. 20°C (room temperature water bath) could be used as a control experiment
6. find the mean time at each temperature to calculate the average rate of respiration using the formula rate = 1/mean time
7. plot a graph of temperature (x-axis) against rate of respiration (y-axis)

Question 25

anaerobic yeast

Question 26

respirometer