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HNC Applied Science in Biology and Chemistry > Biochemistry - Outcome 3 > Flashcards

Biochemistry - Outcome 3 Flashcards

Cellular Respiration and Photosynthesis (60 cards)

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1
Q

what are exergonic reactions?

A

reactions that give out energy

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2
Q

what are endergonic reactions?

A

reactions that take in energy

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3
Q

what molecule participates in the most energy transfers?

A

adenosine triphosphate (ATP)

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4
Q

how is ATP linked to anabolic and catabolic reactions?

A
  • simple molecules eg. glucose, amino acids, fatty acids
  • anabolic reactions transfer energy from ATP to complex molecules
  • complex molecules and polymers eg. glycogen, protein, TAGs
  • catabolic reactions transfer energy from complex molecules to ATP
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5
Q

what are the bonds between the two terminal phosphates called?

A

phosphoanhydride bonds

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6
Q

why is ATP used as the universal metabolic fuel in preference to acid anhydrides?

A
  • it has a longer biological half life compared to acid anhydride
  • more kinetically stable - won’t break down as quickly and will last longer
  • releases energy at a slower rate
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7
Q

what is meant by the term oxidation?

A

the removal of electrons or hydrogen from and atom or molecule

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8
Q

what is meant by the term reduction?

A

the addition of electrons or hydrogen to a molecule

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9
Q

what are the three stages of cellular respiration?

A
  • glycolysis
  • citric acid cycle
  • electron transport chain
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10
Q

is oxygen required in glycolysis?

A

no
- known as anaerobic cellular respiration

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11
Q

how many chemical reactions does glycolysis consist of and what happens during them?

A
  • 10 chemical reactions
  • they split glucose into 2 pyruvate molecules
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12
Q

where does glycolysis occur in a cell?

A

cytosol

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13
Q

what is produced during glycolysis?

A
  • 4 ATP molecules are produced - 2 ATP molecules are used up giving net yield of 2 ATP
  • 2 NADH molecules and 2H+ are produced
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14
Q

what happens if there is oxygen present during glycolysis?

A

pyruvate enters the mitochondrial matrix and is converted into acetyl coenzyme A

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15
Q

what happens if there is inadequate oxygen present during glycolysis?

A

pyruvate is converted into lactate
- the reaction restores NAD+ consumed in step 6 of glycolysis

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16
Q

what happens in organisms that can grow anaerobically, such as yeast, and what is this process called?

A
  • pyruvate is converted (via acetylaldehyde) into carbon dioxide and ethanol
  • reaction regenerates NAD+ from NADH so that glycolysis can continue
  • known as alcoholic fermentation
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17
Q

how is pyruvate converted to acetyl coenzyme A?

A
  • carbon dioxide is removed
  • acetyl group is then attached to coenzyme A to produce acetyl coenzyme A
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18
Q

what is the reaction called if it involves an oxidation and loss of carbon dioxide?

A

oxidative decarboxylation

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19
Q

where does the citric acid cycle occur in a cell?

A

mitochondrial matrix

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20
Q

what does the citric acid cycle allow?

A

intermediates from not only carbohydrate metabolism but also fat and amino acid metabolism to be completely oxidised to carbon dioxide and water

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21
Q

to what type of molecule is the chemical energy stored in the intermediates transferred?

A

reduced coenzymes = NADH+ and FADH2

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22
Q

what molecule is produced from the citric acid cycle and converted into ATP?

A

GTP

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23
Q

where do reduced coenzymes transfer their stored energy to?

A

the electron transport chain

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24
Q

what starts the citric acid cycle?

A

a reaction with acetyl CoA with oxaloacetate that produces citric acid

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25
what does each cycle of the citric acid cycle produce?
- 2 molecules of CO2 - 3 molecules for NADH + H+ - 1 molecule GTP - 1 molecule of FADH2
26
what is the electron transport chain?
a series of electron carriers that are integral membrane proteins situated within the mitochondrial membrane
27
what does the inner mitochondrial membrane fold into?
cristae
28
what happens in the electron transport chain?
- NADH molecules bind to complex I and release their hydrogen atoms as protons (H+) and electrons (e-) - NAD molecules then return to the citric acid cycle to collect more hydrogen - FADH2 binds to complex II to release its hydrogen - electrons are passed down the chain of proteins complexes from I to IV, each complex binding electrons more tightly than the previous one
29
what happens in protein complexes I, II , and III in the ETC?
electrons give up some of their energy, which is then used to pump hydrogen ions across the inner mitochondrial membrane by active transport through the complexes
30
what happens in protein complex IV in the ETC?
electrons are combined with H+ and molecular oxygen to form water
31
what molecule acts as the final electron and proton acceptor?
oxygen
32
in the ETC, what are the energy of electrons stored in the form of?
a proton gradient or a hydrogen ion gradient
33
how is ATP generated?
through protons flowing through ATP synthase
34
how much ATP is produced by each molecule of NADH + H+ and by FADH2?
- NADH + H+ produces 3ATP - FADH2 produces 2ATP
35
compare the overall energy yields and anaerobic and aerobic respiration?
anaerobic respiration - glycolysis - produced by oxidising one glucose molecule = 2ATP aerobic respiration glycolysis oxidation of glucose to 2 pyruvate - substrate level oxidation = 2 ATP - plus 2 NADH = 6 ATP 2 pyruvate to 2 acetyl CoA 2 NADH = 6 ATP citric acid cycle 3 NADH = 9 ATP 1 FADH2 = 2 ATP 1 GTP = 1 ATP = 12 ATP each glucose produces 2 pyruvate so total = 24 ATP total energy produce by oxidising one glucose molecule = 38 ATP
36
what organisms carry out photosynthesis?
plants, algae and bacteria
37
what are two distinct reactions that make up photosynthesis?
- light reaction - light independent reaction
38
what happens in the light reaction?
light energy drives the synthesis of ATP and NADPH (nicotinamide adenine dinucleotide phosphate)
39
what happens in the light independent reaction?
NADPH and ATP produced during the light reaction are used to synthesis carbohydrate from carbon dioxide and water
40
where does photosynthesis occur?
chloroplasts
41
what are chloroplasts ?
disc shaped structures which appear green due to the presence of the pigment chlorophyll
42
what is each chloroplast surrounded by?
a double membrane, enclosing the storm in which is a system of flattened membranous sacs called thylakoids
43
where does the light reaction occur?
thylakoid membrane
44
where does the light independent reaction occur?
the stroma
45
what is a granum?
stack of thylakoids
46
what is absorbed by chlorophyll?
photons
47
where is the chlorophyll located ?
in multiprotein complexes called photosystems found within the thylakoid membrane
48
what are the two linked components in a photosystem?
- antenna complex - photochemical reaction centre
49
describe the structure of the antenna complex
contains chlorophyll and acts like a satellite dish to absorb energy
50
describe what happens when a photon of light is absorbed by chlorophyll in the antenna complex?
- photon excites electrons and promotes them to a higher energy level which makes them unstable in a chlorophyll molecule - energy is then transferred to a neighbouring molecule whose electron is excited whilst original molecule returns to base state - passage of energy from molecule to molecule continues rapidly and randomly around antenna complex until energy is received by photochemical reaction centre
51
what is the photochemical reaction centre?
- a transmembrane protein complex containing a chain of electron carriers - contains 2 specific molecules of chlorophyll
52
what happens in the photochemical reaction centre when the electrons are excited?
- they pass along a series of electron carriers releasing energy at each step - energy is initially harnessed to pump hydrogen ions across thylakoid membrane into the thylakoid to create a hydrogen ion gradient - hydrogen ions flow back through ATP synthase to produce ATP - final electron acceptor is oxygen
53
how is photosynthesis started?
energy from sunlight is captured by photosystem II and is passed on to 3 electron carriers: - plastoquinone - cytochrome bf complex - plastocyanin further energy is captured by photosystem I - used to re-energise electrons from plastocyanin to a higher potential energy state - electrons pass to another energy carrier called ferredoxin and then to NADP+ to reduce it to NADPH
54
why do plants need to undergo cyclic photophosphorylation?
so that the demand for ATP is met as only a small amount of ATP is produced from non-cyclic photophosphorylation
55
what happens during cyclic photophosphorylation?
- instead of the electrons from ferredoxin being used to reduce NADP+ they are recycled back to plastoquinone in photosystem II - they can then be passed through the bf complex to produce more ATP
56
what happens in the Calvin cycle?
- ribulose diphosphate carboxylase (rubisco) located in the stroma condenses a molecule of CO2 with ribulose 1,5 diphosphate to produce a transient six carbon intermediate that rapidly hydrolyses into two molecules of 3-phosphoglycerate - 3 molecules of rubisco (3x5C) condense with 3 molecules of CO2 (3x1C) to produce 6 molecules of 3-phosphoglycerate (6x3C) - cycle converts the 6 3-phosphoglycerate into 6 glyceraldehyde 3-phosphates (6x3C) - 5 of the glyceraldeyhyde 3-phosphates are used to regenerate three rubisco (3x5C) - 1 glyceraldeyhyde 3 -phosphate is combined with another glyceraldeyhyde 3 -phosphate to produce fructose 6-phosphate and eventually fructose and starch
57
what are the 3 limiting factors of photosynthesis?
- light levels - CO2 levels - temperature
58
how are light levels a limiting factor of photosynthesis?
- without enough light plant can't photosynthesise fast even with plenty H2O and CO2 - increasing light intensity, increasing photosynthesis - can get to a point where rate of photosynthesis does not increase as light intensity increases - could be due to photosynthesis reaching maximum rater or other factor limiting rate
59
how are CO2 levels a limiting factor of photosynthesis?
- if ran out of CO2 plant can't photosynthesise - increasing CO2 concentration, increases rate of photosynthesis until photosynthesis reaction has reached its maximum rate to some other factor limiting rate
60
how is temperature a limiting factor of photosynthesis?
- if too cold photosynthesis will slow down because enzymes involved slow down - if too hot plants cannot photosynthesis because enzymes denature

HNC Applied Science in Biology and Chemistry (22 decks)

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