Topic 5 - Energy for Biological Processes

Question 1

What is energy

Answer 1

The ability to do work

Question 2

Why do we need energy

Answer 2

• Metabolism
• Movement
• Active transport
• Maintenance, repair and division of cells
• Production of substances
• Maintenance of body temperature

Question 3

Structure of ATP

Answer 3

• Mononucleotide (nucleotide occurs singly)
• x3 phosphates
• Adenine
• Ribose sugar

Question 4

ATPase ?

Answer 4

The enzyme that catalyses the breakdown of ATP (ATP synthase catalyses the synthesis of ATP)

Question 5

Redox reactions?

Answer 5

Reduction and oxidation reactions in which one reactant loses electrons (is oxidised) and another gains electrons (is reduced)

Question 6

Where does the energy to produce ATP usually come from?

Answer 6

Usually from breakdown ~(catabolic) or redox reactions

Question 7

Advantages of ATP

Answer 7

• Instant source of energy
• Releases energy in small amounts as needed
• Resynthesized
• It is mobile and transports chemical energy to where it is needed in the cell
• Universal energy carrier and can be used in many different chemical reactions

Question 7

What is respiration

Answer 7

• The process by which energy in organic molecules is made available for an organism to do biological work
• Cellular respiration occurs in every living cell to produce ATP

Question 7

Uses of ATP

Answer 7

• Muscle contraction
• Control of cytoskeleton
• Active transport
• Photosynthesis
• RNA synthesis
• Protein synthesis
• DNA synthesis

Question 7

Aerobic respiration

Answer 7

Refers to the cellular respiration that depends on oxygen

Glucose + oxygen > carbon dioxide + water + ATP

Question 8

Why doesn’t respiration produce flames like combustion?

Answer 8

• Cells have to oxidise glucose in a much more controlled way so that the heat generated does not destroy them
• The heat is spread over many biochemical reactions which occue in a series of steps

Question 9

What are some features of the structure of mitochondria?

Answer 9

• Outer membrane
• Inner membrane
• Compartment between inner and outer membrane
• Mitochondrial matrix
• Stalked particles

Question 10

Summary of glycolysis

Answer 10

• Occurs in the cytoplasm and does not require oxygen
  1) Glucose (6 carbon sugar) phosphorylated by 2 molecules of ATP
  2) This molecule is unstable and immediately breaks down into 2 molecules of glycerate 3-phosphate (2 x 3 carbon molecules)
  3) 2 Glycerate 3-phosphate oxidised into 2 pyruvate (3 carbon molecules)
  4) 2 NAD coenzymes are oxidised into 2 reduced NAD (NADH)
  5) 2 molecules of ADP are phosphorylated to 2 molecules of ATP

Question 11

What is the link reaction?

Answer 11

It links glycolysis in the cytoplasm with the krebs cycle in the mitochondria (matrix of mitochondria)
Glucose is too large and there’s no transport proteins to allow it to enter the mitochondria (link reaction allows this)

Question 12

Describe process of link reaction

Answer 12

Pyruvate converted into acetyl coenzyme A with help of NADH (dehydrogenation), loss of carbon dioxide (decarboxylation) and addition of CoA

Question 12

Describe process of Krebs cycle

Answer 12

• Consists of a series of enzyme-controlled reactions
• 2 carbon (2C) Acetyl CoA enters the circular pathway from the link reaction
• 4 carbon (4C) oxaloacetate accepts the 2C acetyl fragment from acetyl CoA to form the 6 carbon (6C) citrate (coenzyme A is released in this reaction)
• Citrate is then converted back to oxaloacetate through a series of oxidation-reduction (redox) reactions

Question 13

Regeneration of oxaloacetate

Answer 13

Oxaloacetate regenerated through redox reactions
- Decarboxylation of citrate (6C) , releasing 2 CO2 as waste gas
- Oxidation (dehydrogenation) of citrate
- Releasing H+ that reduce coenzymes NAD and FAD
- 3 NAD and 1 FAD & H+ > 3NADH and 1FADH2 substrate-level phosphorylation
- Phosphate transferred from one of the intermediates to ADP forming 1 ATP

Question 14

Products of Krebs cycle

Answer 14

• ATP
• 3 NADH
• 1 FADH2
• CO2

(for each glucose molecule there are 2 turns of the krebs cycle)

Question 15

Electron Transport Chain (oxidative phosphorylation) requires:

Answer 15

• In presence of oxygen, energy is released to allow phosphorylation of ADP
• Oxygen (to accept the electrons and hydrogen at the end)
• Reduced NAD and FAD which are carrying hydrogen
• Electron carriers (cytochromes)

Question 16

Describe oxidative phosphorylation

Answer 16

• Reduced NAD/FAD, transfer H+ ions/electrons
• From coenzyme to coenzyme/ carrier to carrier/ along an electron transport chain by series of redox reactions
• driven by oxygen as terminal acceptor pf electrons
• H+/protons passed into intermembrane space
• H+/protons flow back through stalked particles/ ATP synthase
• by chemiosmosis this energy used to synthesise ATP from ADP and inorganic phosphate by condensation reaction

Question 17

Products of the electron transport chain

Answer 17

• ATP
• Water
• NAD
• FAD

Question 18

Chemiosmosis

Answer 18

Process that moves hydrogen ions through the membrane along a concentration gradient. It links the electron transport chain with production of ATP

Question 19

What’s oxygen used for in electron transport chain?

Answer 19

Acts as terminal electron/proton acceptor to form the safe by-product water.

Question 20

Anerobic respiration

Answer 20

Takes place in the absence of oxygen
It involves glycolysis and generates ATP and NADH.
Because of lack of oxygen NADH is oxidised by fermentation a process in which no more ATP molecules generated

Question 21

2 types of anerobic fermentation

Answer 21

1) Alcoholic fermentation (2CO2 released) 2) Lactate fermentaion

Question 22

Ethanol fermentation

Answer 22

- Reduced NAD transfers its hydrogens to ethanol to form ethanal - First step of the pathway pyruvate is decarboxylated to ethanol producing CO2 - Then ethanal reduced to ethanol by enzyme alcohol dehydrogenase - Ethanal is hydrogen acceptor - Ethanol cannot be further metabolised - waste product

Question 23

Lactate fermentation

Answer 23

- reduced NAD transfers its hydrogen to pyruvate to form lactate - Pyruvate reduced to lactate by enzyme lactate dehydrogenase - Pyruvate is a hydrogen acceptor - Final product lactate can be further metabolised

Question 24

Autotroph

Answer 24

An organism which makes complex organic compounds e.g. glucose from simple inorganic compounds

Question 25

Heterotroph

Answer 25

An organism that obtains complex organic compounds e.g. glucose by feeding on other organisms or their dead remains

Question 26

Photosynthesis overview

Answer 26

- Series of chemical reactions that occur in autotrophs such as plants and algae - Converts light energy into chemical energy which is then stored in biomass of autotrophs (producers) - Light energy used to split strong bonds in water - Oxygen released into the atmosphere as a waste products - Hydrogen combined with carbon dioxide to produce glucose - Chemical energy stored in bonds in glucose molecules - therefore function as a fuel for respiration - Hydrogen stored in glucose molecules

Question 27

Light dependent reaction

Answer 27

1) electrons are excited to higher energy level by energy trapped by chlorophyll molecules in the thylakoid membranes. 2) Electrons passed down electron transport chain from one electron carrier to the next 3) process generate ATP from ADP and inorganic phosphate in a process called photophosphorylation 4)This can be cyclic or non-cyclic 5) Reduced NADP also generated in light-dependent stage as electrons transferred to NADP along with a proton 6) Both ATP and reduced NADP used in light-independent stage of photosynthesis

Question 28

Cyclic phosphorylation

Answer 28

1) A photon of light hits a chlorophyll molecule 2) Electrons are excited 3) Electrons taken up by an electron acceptor 4) Electrons passed along an electron transport chain. Energy is released, ATP is synthesised 5) Electron returns to photosystem l chlorophyll

Question 29

Non-cyclic phosphorylation

Answer 29

1) Photon hits chlorophyll in photosystem ll 2) Electrons are excited 3) Electrons taken up by an electron acceptor , passed along an electron transport chain to photosystem l chlorophyll. Energy released, ATP is synthesised 4) Photon hits chlorophyll in photosystem l 5) Photolysis - water dissociates into hydrogen and hydroxide ions. Replaces lost electrons in photosystem ll chlorophyll 6) Electrons are excited 7) Electrons are taken up by an alectron acceptor, passed along an electron transport chain to NADP 8) NADP takes up an H+ ion from dissociated water and forms reduced NADP 9) Hydroxide ions react together to from water and oxygen

Question 30

Light independent reaction

Answer 30

AKA Calvin-Benson cycle Final stage of photosynthesis which uses ATP (source of energy) and reduced NADP (reducing power) to produce glucose. 1) RuBP combined with carbon dioxide (carbon fixation), catalysed by RUBISCO 2) RuBP converted into 2 glycerate 3-phosphate (GP) molecules 3) Reduced NADP and ATP used to convert GP to GALP 4) Some GALP molecules used to make glucose, then converted to organic compounds like lipds, amino acids & nucleic acids 5) Remaining GALP molecules used to reform RuBP with help of ATP