Download 7-cellular-respiration

Human Cells
Cellular Respiration
1
What do you know?
 In Pairs
 From N5 Brain Storm what you know of respiration and
put it on the sheets of A2 paper.
 Review with class
2
What are you going to learn?
 More detail about the 3 different stages of cellular
respiration including the names of the enzymes involved.
 More detail about how ATP is synthesised.
 About some alternative substrates for respiration.
 About the regulation of the chemical pathways involved
with respiration.
3
Introduction and ATP
 Why is respirations so important to cells?
 It regenerates ATP from ADP and Pi
 How do they do that?
 They take ‘food’ i.e. glucose and through a series of
metabolic pathways release energy which used to
regenerate ATP
 What do cells use the energy rich ATP for?
 Building proteins, cellular respiration etc. ….
4
ATP
 Glucose is broken down, releasing hydrogen ions and
electrons by dehydrogenase enzymes.
 The electrons provide the energy to regenerate ATP from
ADP + Pi.
requires energy
low energy ADP + Pi
ATP high energy
state
releases energy
state
 The metabolic pathways for cell respiration are linked to
many other pathways because they produce the energy
needed for them as ATP.
 ATP = adenosine triphosphate
5
ATP
 ATP is the molecule that transfers energy between
catabolic and anabolic metabolic pathways in cells.
carbon dioxide
and water
(catabolic)
glucose and
oxygen
ATP
amino acids
(anabolic)
ADP + Pi
protein
 ATP is able to release energy by removing a Pi molecule.
6
ATP
 ATP makes phosphate available to phosphorylate other
molecules in a process called phosphorylation.
 Phosphorylation is where a phosphate group is added to
another molecule.
HOW MUCH ATP?
 ATP is continuously being used and regenerated.
 This may occur at a rate equivalent to 400g/h.
 The store of ATP in the body is thought to remain at
approximately 50 g at any one time.
7
What type of reactions need energy?
8
What do you know now?
 What is the purpose of cellular respiration?
 What is the primary substrate for respiration?
 What is released from the substrate?
 What are the enzymes called that do this?
 What is regenerated in respiration?
 What is phosphorylation?
 What are catabolic reactions?
 What are anabolic reactions?
 Name examples of these reactions
9
Mitochondria
10
Cellular respiration
 The three stages of cellular respiration are called
 Glycolysis
 Citric acid cycle
 Electron transport chain
TRIOS
Sit in groups of 3 and number yourselves 1, 2, 3
1s are glycolysis and sit table 1
2s are citric acid cycle and sit at table 2
3s electron transport system and sit at table 3
On A2 paper summarise your section, use diagrams etc.
Come back together and share your section, 1 then 2 then 3
11
Glycolysis
 In cytoplasm
 Splitting of glucose to form pyruvates
 A series of enzyme controlled steps
 2 ATP used in energy investment phase
 4 ATP generated in energy pay off stage
 Net gain of 2 ATP
 Some H+ ions released by dehydrogenase in energy pay
off stage carried by coenzyme molecule NAD to give
NADH
12
Glycolysis
13
Phosphorylation in glycolysis
 Occurs twice in glycolysis.
 First phosphorylation occurs when phosphate is added to
glucose producing an intermediate compound that can go
into a number of metabolic pathways.
 Second phosphorylation occurs with enzyme
phosphofructokinase adds another phosphate. This is
irreversible and leads to the production of pyruvate in the
glycolytic pathway.
 Pyruvate will progress into the citric acid cycle if oxygen is
present.
 Fermentation will occur if no oxygen is present.
14
Citric Acid Cycle
 Occurs in the matrix of the mitochondria.
 Pyruvate is broken down to an acetyl group.
 Each acetyl group combines with Coenzyme A to give




Acetylcoenzyme A.
Acetylcoenzyme A combines with oxaloacetate to
produce citrate
Citrate goes through a series of enzyme mediated
reactions to produce oxaloacetate. This produces CO2,
NADH, FADH2 and ATP
Dehydrogenase enzyme removes hydrogen ions and high
energy electrons which are passed to coenzymes NAD or
FAD to produce NADH and FADH2.
Both are used later in the electron transport chain.
15
Citric Acid Cycle
16
Electron Transport Chain
 On inner membrane of the mitochondria.
 Produces most of the ATP fro aerobic respiration.
 High energy electrons are used to pump hydrogen ions




across the inner membrane.
The flow of ions allows ATP synthase to rotate and
catalyse the regeneration of ADP and Pi into ATP.
The final electron receptor is oxygen.
Oxygen combines with the hydrogen ions to produce
water.
This produces 36 molecules of ATP
17
Electron transport chain
18
Substrates for Respiration
 Glucose is the usual respiratory substrate used by cells
from either the breakdown of starch or glycogen.
 Other sugars can be used as these can produce glucose or
other intermediates.
 Proteins form amino acids when broken down.
Deamination in the liver produces molecules that can be
used either in glycolysis or the citric acid cycle as
respiratory substrates.
 Fats can be broken down to glycerol and fatty acids.
These can be used as intermediates in glycolysis and the
citric acid cycle respectively.
19
Glucose as the respiratory substrate
starch
maltose
glycogen
glucose
sucrose
fructose
pyruvate
20
Protein as a respiratory substrate
glucose
protein
Amino acids
e.g. alanine
pyruvate
Amino acids
e.g. leucine
Acetyl
coenzyme A
Amino acids
e.g. aspartic
acid
intermediate
Citric acid
cycle
21
Fat as a respiratory substrate
glucose
glycerol
fat
intermediate
pyruvate
fatty acids
acetyl coenzyme A
Citric acid cycle
22
Regulation of cellular respiration
by feedback inhibition
 Like many biochemical pathways cellular respiration is
regulated by feedback inhibition
 If ATP is not being used then the high concentration will
inhibit the activity of phosphofructokinase which will
slow down glycolysis.
 If ATP concentration decreases the enzyme will no longer
be inhibited and glycolysis will speed up.
23
Regulation of cellular respiration
by feedback inhibition
 A high concentration of citrate will inhibit
phosphofructokinase but if the citrate concentration falls
the enzyme will not be inhibited. Glycolysis will speed up
supplying more acetyl groups for the citric acid cycle.
 This feedback inhibition has the advantages of conserving
resources, producing ATP when needed and not building
up too many intermediate compounds.
 So the inhibition of the phosphofructokinase
synchronises the rates of glycolysis and citric acid cycle
24
What do I need to know?
Glycolysis










Where does this stage occur?
What is glucose broken down to?
What is meant by the energy investment phase?
What occurs during step 1?
Where does the second phosphorylation occur?
What is the name of the enzyme that catalyses the second
phosphorylation?
Is the second phosphorylation reversible/irreversible?
What occurs in the energy payoff phase?
What happens to the pyruvate produced?
How many ATP are produced during this phase?
25
What do I need to know?
Citric acid cycle
 Where does this stage occur?
 What happens to the pyruvate?
 What does the acetyl coA combine with and what odes it







produce?
A series of intermediates are produced, what controls theses
reactions?
Why is carbon dioxide produce at this stage?
Why is it important that oxaloacetate is continually produced?
What are the names of the two coenzymes involved?
What do these coenzymes do?
What enzymes remove the hydrogens?
What else is generated at this stage?
26
What do I need to know?
Electron transport chain









Where does this stage occur?
What is the electron transport chain?
What do NADH and FADH2 do here?
What are the electrons used for?
What is the fate of the H+ ions?
What does the return flow of H+ ions cause to happen?
How is ATP synthesised?
What is the final electron acceptor?
What does the final electron acceptor combine with and what
does this produce?
 How many ATP molecules are generated in the Aerobic phase
of respiration?
27
What do I need to know?
Substrates
 What are the possible substrates for respiration?
 For each of the possible substrates state the following:
 What must happen to them first?
 Where in the cycle they enter?
 In what circumstances are these substrates uesd?
28
What do I need to know?
Regulation
 Why does the production of ATP need to be regulated?
 When would the supply of ATP increases/decrease?
 What happens if the cell produces too much ATP?
 Describe the mechanism of inhibition of the enzyme
phosphofructokinase by citrate
 How does the inhibition of phosphofructokinase by
citrate synchronise the rate of both glycolysis and the
citric acid cycle?
29