Transcript Poisonous mushrooms

Poisonous mushrooms
Poisonous mushrooms
Bill Indge
Poisonous mushrooms
Bringing it all together
Molecules
Ecology
Cells
Poisonous
mushrooms
Genes and
genetics
Physiological
systems
Poisonous mushrooms
Amino acids and peptide bonds
R
R
H
H
O
N
C
H
C
H
O
N
C
OH H
H
C
OH
Poisonous mushrooms
Amino acids and peptide bonds
R
R
H
H
O
N
C
H
C
H
O
N
C
OH H
H
C
OH
Poisonous mushrooms
Amino acids and peptide bonds
R
R
H
H
O
N
C
H
C
H
Peptide
bond
O
N
C
C
H
OH H
OH
Poisonous mushrooms
1 (c) In the simplest cyclic polypeptides, the amino acids
bind together to form a ring.
How many peptide bonds would there be in a
cyclic polypeptide containing eight amino acids?
Explain how you arrived at your answer.
(2 marks)
Amino acid
Peptide bond
joining two
amino acids
Poisonous mushrooms
Digesting peptides and polypeptides
Endopeptidases break peptide
bonds in the middle of a
polypeptide chain producing
smaller polypeptides
Exopeptidases break peptide
bonds in the end
of a polypeptide chain
releasing amino acids
Poisonous mushrooms
Exopeptidases break peptide
bonds in the end
of a polypeptide chain
releasing amino acids
2
-amanitin is not broken down
by endopeptidases. Use this
information to suggest
why exopeptidases do not
digest -amanitin. (2 marks)
Endopeptidases break peptide
bonds in the middle of a
polypeptide chain producing
smaller polypeptides
Cyclic
polypeptide so
no smaller
polypeptides
produced;
No free amino/
carboxylic acid
groups;
Will not bind
with enzyme;
Poisonous mushrooms
Bile salts and their circulation
• Bile salts are produced
in the liver and enter
the duodenum
• Most of the bile salts
are reabsorbed in the
lower part of the small
intestine
• These bile salts are
returned to the liver in
the blood
3 (a)
intestine
liver
(Stored in gall
bladder) then
through bile
duct
Describe the route by which bile salts produced
in the liver enter the duodenum. (1 mark)
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Bile salts and their circulation
• Bile salts are produced
in the liver and enter
the duodenum
• Most of the bile salts
are reabsorbed in the
lower part of the small
intestine
liver
Hepatic portal
vein
• These bile salts are
returned to the liver in
the blood
3 (b)
Name the blood vessel through which bile salts
are returned to the liver. (1 mark)
intestine
Poisonous mushrooms
4
There is a delay of 2–6 days between eating fungi
containing -amanitin and the development of
symptoms associated with liver damage.
(a)
Explain why this delay might suggest that it would be
inappropriate to treat patients showing symptoms with
substances that remove poisons from the gut.
(2 marks)
• Takes less than 2 days/short time for substances in gut to be
absorbed;
• Will pass out as faeces;
• So would not expect any -amanitin to still be in gut
Poisonous mushrooms
(b) In spite of this delay, patients are often given oral doses
of activated charcoal. Activated charcoal absorbs
poisonous substances in the gut which are then safely
removed from the body in faeces.
Use information provided in this question to explain why
giving activated charcoal might still be a useful
treatment for a person who has eaten fungi
containing -amanitin.
(2 marks)
• -amanitin is recycled/passes back into the gut;
• Activated charcoal may remove the -amanitin that
re-enters the gut;
• So would not reach such high concentrations in the liver;
Poisonous mushrooms
Getting into liver cells
Concentration of amanitin/µmol dm–3
Rate of uptake of -amanitin/
µmol min–1 mg–1 protein
50
1.0
100
2.2
150
3.0
200
3.8
400
4.4
600
5.0
800
5.0
Poisonous mushrooms
Make sure that you understand the data
Read the stem
It is suggested that -amanitin enters cells by facilitated diffusion,
making use of the same transport protein as bile salts.
Scientists investigated factors affecting the rate of uptake of
-amanitin through liver cell membranes. In the first experiment they
looked at the effect of the concentration of -amanitin on its rate of
uptake. Their results are shown in the table.
Poisonous mushrooms
Check the table headings in the stem
Concentration should be
clear enough
Concentration of -amanitin/
µmol dm–3
Rate of uptake of -amanitin/
µmol min–1 mg–1 protein
50
1.0
100
2.2
150
3.0
200
3.8
400
4.4
600
5.0
800
5.0
Poisonous mushrooms
Check the table headings in the stem
This is rate of uptake, not the total
amount of -amanitin taken up
Concentration of -amanitin/
µmol dm–3
Rate of uptake of -amanitin/
µmol min–1 mg–1 protein
50
1.0
100
2.2
150
3.0
200
3.8
400
4.4
600
5.0
800
5.0
Poisonous mushrooms
Make sure that you know what the table as a whole is
telling you
Put the information in
this box into words
Concentration of -amanitin/
µmol dm–3
Rate of uptake of -amanitin/
µmol min–1 mg–1 protein
50
1.0
100
2.2
150
3.0
200
3.8
400
4.4
600
5.0
800
5.0
Poisonous mushrooms
Concentration of -amanitin/
µmol dm–3
Rate of uptake of -amanitin/
µmol min–1 mg–1 protein
50
1.0
100
2.2
150
3.0
200
3.8
400
4.4
600
5.0
800
5.0
5 (a) Describe the effect of -amanitin concentration on its
uptake by liver cell membranes.
(2 marks)
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Describe
Follow these guidelines
• Look for the overall trend or pattern

Sometimes it
helps to sketch
a simple graph
• Describe this in terms of the column headings
• Quote values where they peak or the gradient changes
and 2 marks are guaranteed.
Poisonous mushrooms
Concentration of -amanitin/
µmol dm–3
Rate of uptake of -amanitin/
µmol min–1 mg–1 protein
50
1.0
100
2.2
150
3.0
200
3.8
400
4.4
600
5.0
800
5.0
5 (a) Describe the effect of -amanitin concentration on its uptake
by liver cell membranes. (2 marks)
The rate of uptake increases and then levels out (as the concentration of
-amanitin increases);
Between 400 and 600 µmol dm–3;
Poisonous mushrooms
Concentration of -amanitin/
µmol dm–3
Rate of uptake of -amanitin/
µmol min–1 mg–1 protein
50
1.0
100
2.2
150
3.0
200
3.8
400
4.4
600
5.0
800
5.0
(b) Explain the change in the rate of uptake at concentrations
of -amanitin between 400 and 800 µmol dm–3.
(2 marks)
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Explain
Follow these guidelines:
•Explain means ‘Give a reason why’. A description, however
good, will not gain marks.
•Start your answer with the word ‘Because’.
•If you are asked to use a table, or a graph or diagram,
make sure you do.
•It is a good idea to include a phrase such as ‘in the table’ or
‘the graph shows’. This will show your examiner that you are
using the relevant information.
•Describe this in terms of the column headings.
•Quote values where they peak or the gradient changes.
If you do all this, 2 marks are guaranteed.
Poisonous mushrooms
Concentration of -amanitin/
µmol dm–3
Rate of uptake of -amanitin/
µmol min–1 mg–1 protein
50
1.0
100
2.2
150
3.0
200
3.8
400
4.4
600
5.0
800
5.0
(b) Explain the change in the rate of uptake at concentrations
of -amanitin between 400 and 800 µmol dm–3.
(2 marks)
Because -amanitin is taken up by facilitated diffusion;
At concentrations above 400 µmol dm–3 the carriers are saturated
with -amanitin;
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Getting into liver cells
Rate of uptake of amanitin/
µmol min–1 mg–1 protein
800
Don’t forget
• Stem
• Axes
• Graph as a whole
600
Amanitin only
400
200
Amanitin + bile salts
0
0
30
60
Time/s
90
120
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6 (a) Explain why the
units for -amanitin
uptake are given per
gram of protein.
(2 marks)
Rate of uptake of amanitin /
µmol min–1 mg–1 protein
Getting into liver cells
800
(b) Explain how the
results shown in the
graph support the
Amanitin only
suggestion that
-amanitin enters
cells by facilitated
diffusion, making use
of the same transport
Amanitin + bile salts protein as bile salts.
(2 marks)
600
400
200
0
0
30
60
Time/s
90
120
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6 (a) Explain why the units for -amanitin uptake are given per gram of
protein. (2 marks)
Because this allows the results to be compared;
As uptake depends on the number of carrier proteins present/
the number of carrier proteins may vary from membrane to membrane;
6 (b) Explain how the results shown in the graph support the suggestion
that -amanitin enters cells by facilitated diffusion, making use of the
same transport protein as bile salts. (2 marks)
Because the graph shows that the rate of uptake is lower when bile
salts are present;
-amanitin and bile salts are competing for the same transport protein;
Poisonous mushrooms
6 (c) The fetus is not harmed if a pregnant women eats fungi containing
-amanitin. Suggest why the fetus is not poisoned by -amanitin.
(2 marks)
This question requires you to apply knowledge to a new situation.
• The question will be based on information you should know.
• You will be given all other information you need.
-amanitin cannot pass through the placental membranes;
No -amanitin/bile salt carrier proteins present;
All you needed to know was that substances reach a developing
fetus by way of the placenta.
Poisonous mushrooms
Bringing it all together
Molecules
Protein structure
Ecology
Poisonous
mushrooms
Genes and
genetics
Protein synthesis
Cells
Facilitated
diffusion
Physiological
systems
The gut and digestion