ATP use, synthesis and structure

A2 Human Biology

Miss Tagore

Learning Outcomes

1. Outline the need for ATP in living organisms, as illustrated by anabolic reactions, active transport, movement, and the maintenance of body temperature;

2. Describe, with the aid of diagrams, the structure of ATP;

3. State that ATP provides the immediate source of energy for biological processes.

Uses for ATP

Adenosine triphosphate is the body’s most common energy source. It is used in every cell in the body for activities such as:

Active transport

Maintaining body temperature

Anabolic reactions (synthesis of smaller molecules into larger ones)

http://www.bbc.co.uk/schools/gcsebitesize/science/videos/aerobic_video1.shtml

The Structure of ATP

The structure of ATP is similar to that of a nucleotide. What two features are similar?

ATP is water soluble and so is easily transported across membranes within a cell.

Free electrons surround the phophate groups – these give the molecule its high energetic potential.

Nitrogenous base

5-carbon Ribose sugar

3 phosphate groups

The Structure of ATP

Adenosine

Adenosine monophosphate (AMP)

Adenosine diphosphate (ADP)

Adenosine triphosphate (ATP)

ATP as a source of energy The phosphate “tail” of an ATP

molecule is where the main source of energy is.

Removal of a phosphate group by the process of hydrolysis (the addition of water) releases energy.

When ATP is hydrolysed to ADP, 30.5KJ of energy is released.

ADP can be further broken down into AMP, which also releases a small amount of energy.

Pi + ADP

ATP as a source of energy The energy released as a result of hydrolysis can be

channelled into other molecules and used directly by cells. Some energy is lost as heat.

ATP is continually being brown down and reformed at a rate of 8000 cycles per day.

30.5KJ released

How is ATP synthesised?

All living organisms use and synthesis ATP in different ways: Plants - photophosphorylation Yeast - glycolysis and fermentation Animals – glycolysis and respiration

Varying amounts of ATP are produced in different reactions, as are the locations and requirements for oxygen.

Plant and animal ATP synthesis both require the enzyme ATP snythase (ATPase).

Questions (from page 135)

1. Explain how an ATP molecule is similar to that of DNA or RNA

2. Describe how the hydrolysis of ATP helps maintain the core body temperature

3. Explain why it is an advantage for an organism to hydrolyse ATP to meet its energy requirements rather than hydrolyse glucose directly

For next time…

Read pages 136 – 139 (do 136-137 on one day and 138-139 on another)

Write down the key points under each heading – try to put this in your own words!

Bring this to class – we will discuss it at the start of the lesson

First stages of respiration

Learning Outcomes

(d) state the locations of glycolysis, the link reaction and the Krebs cycle;

(e) outline glycolysis, with reference to the production of pyruvate and NAD;

(f) outline the link reaction, with reference to the decarboxylation of pyruvate (3C) to acetyl (2C) coenzyme A and the reduction of NAD;

First stages of respiration

Cellular respiration has many stages.

It occurs in the cytoplasm of a cell, the matrix and the cristae of the mitochondria.

Glucose cannot be broken down directly to produce ATP – a series of metabolic reactions must take place that leads the the synthesis of ATP.

Three stages that you should know are glycolysis, Kreb’s cycle and oxidative phosphorylation.

The role of enzymes and coenzymes in respiration Respiration is an enzyme-controlled process. It relies on

different enzymes and coenzymes.

Dehydrogenase enzymes remove hydrogen from other molecules and make this hydrogen available to be passed on to coenzymes (this is important later).

Decarboxylase enzymes hydrolyse the carboxyl group (COOH) from a molecule, usually producing CO2

FAD and NAD are coenzymes that act as hydrogen acceptors for the dehydrogenase enzymes.

FAD and NAD

FAD and NAD enable potential energy to be transferred from one molecule to another.

Coenzymes are important because they can be oxidised and reduced (lose and gain electrons)

Glycolysis

Occurs in the cytoplasm (cystol) of a cell.

Glucose is split in this stage

ATP, pyruvate and reduced NAD are produced (reduction is gain of electrons!)

Glycolysis Glucose enters cells by active transport or diffusion.

To make sure that the glucose does not leave the cell, it is chemically altered.

The glucose molecule becomes phosphorylated. 2 ATP molecules do this.

Phosphorylation is when phosphate groups are added to a molecule. This changes the chemical conformation.

Glycolysis

Phosphorylated glucose is eventually broken down through enzyme controlled steps.

The following are produced in glycolysis: 4 x ATP are released 2 x NADH2 (reduced NAD) 2 x 3-carbon pyruvate molecules

Glycolysis

This stage of respiration is the “setting up” stage

Glucose is prepared for further breakdown to produce more ATP

Reduced NAD created here has the potential to make ATP in later stages

Link reaction

Pyruvate produced in glycolysis contains lots of potential energy that can be channelled into ATP synthesis.

This will not happen without the presence of oxygen.

Only when oxygen is present is pyruvate actively transported to the mitochondria.

Here it undergoes a link reaction to become acetyl coenzyme A

Link reaction Pyruvate loses a hydrogen (becomes dehydrogenated)

Pyruvate also loses carbon as carbon dioxide (becomes decarboxylated)

This results in the formation of a substance called acetyl coenzyme A

Acetyl co-A is fixed in the matrix of the mitochondria. From here it can enter the next stage of aerobic respiration, the Kreb’s cycle.

The hydrogen acceptor molecule is NAD.

Questions

Read over pages 136-137 of your textbook.

Write down the key definitions

Answer questions 1-4

Question 1 - answer

Glycolysis can be described as a metabolic pathway because it is a biochemical reaction that involves a series of enzymes to control processes that are linked together.

Question 2 - answer

Glycolysis means to split glucose into two lots of pyruvate

Question 3 - answer

Substrate level phosphorylation changes the confirmation of a glucose molecule by adding a phosphate group to it (from ATP). This allows glucose to be broken down in glycolysis to pyruvate.

Question 4 - answer

Starting molecules

Products of reactions

Site of reactions

Oxygen required

Glycolysis Glucose, ATP, NAD

2 x pyruvate Cytoplasm / cystol

no

Link reactions Pyruvate Acetyl co-A, CO2 and

reduced NAD

Mitochondria yes

The Krebs Cycle

Learning Outcomes

(g) outline the Krebs cycle, with reference to the formation of citrate from acetate and oxaloacetate and the reconversion of citrate to oxaloacetate (names of intermediate compounds are not required);

(h) explain that during the Krebs cycle, decarboxylation and dehydrogenation occur, NAD and FAD are reduced and substrate level phosphorylation occurs.

The Krebs Cycle

A series of chemical reactions that occur in the matrix of the mitochondrion

Acetyl is completely broken down into carbon dioxide

Hydrogen is removed to form reduced coenzymes

More ATP is synthesised directly

The Krebs Cycle

2C acetyl coenzyme A combines with a 4C compound called oxcaloacetate.

This forms a 6C compound called citrate

The Krebs Cycle 6-carbon citrate is an intermediate compound that is

rapidly decarboxylated in a series of enzyme-linked reactions

This compound is also dehydrogenated

The carrier molecules NAD and FAD combine with the liberated hydrogen

Carbon is released as carbon dioxide

It is eventually broken down to 4C oxaloacetate again.

Dehydrogenation

Decarboxylation

Importance of Krebs Cycle

The Krebs cycle breaks down acetyl co-A to CO2

Decarboxylase and dehydrogenase enzymes also release hydrogen atoms.

Coenzyme hydrogen carriers become reduced (NADH/FADH). This is really important for later stages of ATP synthesis.

Acetyl co-enzyme A can be produced from fatty acids and amino acids. The body will metabolise any substrate available to produce ATP.

The Outcome of the Krebs Cycle Three molecules of reduced NAD

One molecule of reduced FAD

One molecule of ATP produced by substrate-level phosphorylation

Two molecules of CO2

One molecule of regenerated oxaloacetate

Control of the Krebs cycle Allosteric feedback mechanisms:

High levels of ATP inhibit first three stages of Krebs cycle

Following enzymes then become inhibited by high levels of reduced coenzyme (NADH/FADH) to stop the cycle from continuing

This means substrates are only broken down as and when needed

High concentration of citrate inhibits continual glycolysis of glucose, therefore regulating the amount of substrate going through the pathways

What is allosteric inhibition? Enzymes involved in respiration pathways can be

inhibited by an inhibitor binding temporarily to somewhere other than the active site, changing the active site.

What to do…

Answer questions on page 139.

Mark your answers and add to them if you are missing information in a different colour pen.

Lesson starter

Answer these three questions:1. What is the name of the 4C molecule that

combines with acetyl CoA to form a 6C acid?

2. What is the name of the 6C acid?

3. What stage in respiration do the above questions refer to?

Answers

1. Oxaloacetate

2. Citric acid

3. Kreb’s cycle

Oxidative Phosphorylation

Learning Outcomes

(i) outline the process of oxidative phosphorylation, with reference to the roles of electron carriers, oxygen and the mitochondrial cristae;

(j) outline the process of chemiosmosis, with reference to the electron transport chain, proton gradients and ATPsynthase (HSW7a).

Recap…

Krebs cycle occurs in matrix of mitochondrion.

Dehydrogenase enzymes remove hydrogen at various stages

NAD and FAD become reduced (accept hydrogen atoms)

Some products of Krebs cycle are used in oxidative phosphorylationProduct from Krebs cycle Where it goes

1 coenzyme A Reused in the next link reaction

Oxaloacetate Regenerated for use in the next Krebs cycle

2CO2 Released as a waste product

1 ATP Used for energy

3 Reduced NAD To oxidative phosphorylation

1 Reduced FAD To oxidative phosphorylation

Oxidative Phosphorylation

Reduced coenzymes from the Krebs cycle are now full of potential energy to make ATP through oxidative phosphorylation.

Oxidative phosphorylation occurs on the cristae of the mitochondrion and involves a series of enzyme controlled

reactions.

What is oxidative phosphorylation?! It’s a two part process.

First stage is electron transport chain

Second stage is the chemiosmosis

The entire process is called oxidative phosphorylation

The Stages of Oxidative Phosphorylation1. There are cytochrome carriers on

the cristae of the mitochondria. Reduced NAD and FAD become oxidised (lose their hydrogen atoms) when they come into contact with these carriers.

2. The hydrogen atoms split up into protons (H+) and electrons (e-)

The Stages of Oxidative Phosphorylation3. Electrons pass along the cytochrome carriers

and the energy released is used to pump protons (H+) into the intermembrane space.

Oxidation of

NAD/FAD

e- passing through the membrane

H+ building up in the

intermemebane space

Lots of hydrogen ions end up in the innermembrane space. This is the opposite side of where they started.

The Stages of Oxidative Phosphorylation

4. Protons create an electrochemical gradient as they cannot pass back through the membrane. (High concentration of H+) outside, low concentration inside

5. Protons which have built up in the intermembrane space end up diffusing through specialised protein channels back into the matrix.

The Stages of Oxidative Phosphorylation

6. These channels contain a structure on the matrix side which consists of the enzyme ATP synthease and is where ADP is phosphorylated to form ATP

(phosphorylated means that a phosphate group is added)

The Stages of Oxidative Phosphorylation7. As the protons (H+) flow

through these channels they “turn” this enzyme and fuel the process of ATP production. The “used” protons (H+) then combine with electrons (e-) and oxygen atoms to form water.

8. The electrons (e-) move along the membrane’s carriers until they reach the final carrier molecule, oxygen.

This process is referred to as chemiosmosis

e- passing through the membrane lose energy as they progress through each carrier (pink

proteins above)Some of the energy given off allows H+ to

move across the membrane

http://www.youtube.com/watch?v=lRlTBRPv6xM

Group Task

That was A LOT of information to take in!

In groups (3/4), discuss what events took place in the cytochrome system.

Come up with a list of steps to explain this process to the other group.

What to do…

Answer questions on page 141.

Mark your answers and add to them if you are missing information in a different colour pen.

Practice Questions

1. Carbon monoxide inhibits the final electron carrier in the electron transport chain.

(a) Explain how this affects ATP production via the electron transport chain (2)

(b) Explain how this affects ATP production via the Krebs cycle

Answers

(a) the transfer of electrons down the electron transport chain stops (1 mark). There is no energy released to phosphorylate ADP/produce ATP (1 mark)

(b) the Krebs cycle stops (1 mark) because there is no oxidised FAD/NAD coming from the electron transport chain (1 mark)

(remember that when the electron transport chain is inhibited, the reactions that depend on the products of the chain are also affected)

32 ATP can be made from 1 glucose moleculeStages of respiration Molecules produced Number of ATP

molecules

Glycolysis 2 ATP 2

Glycolysis 2 reduced NAD 2 x 2.5 = 5

Link reaction (x2) 2 reduced NAD 2 x 2.5 = 5

Krebs cycle (x2) 2 ATP 2

Krebs cycle (x2) 6 reduced FAD 6 x 2.5 = 15

Krebs cycle (x2) 2 reduced NAD 2 x 1.5 = 3

Total ATP = 32

2.5 ATP are made from each reduced NAD1.5 ATP are made from each reduced FAD