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AS OCR Biology Learning Grids
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Unit 2 Module 1 continued
2.1.15 Nucleotides coding molecules
Nucleic acids in living
organisms
What does DNA stand for?
Where is DNA found in a human cell?
Nucleotides are monomers of
nucleic acids
Which three components make up a
nucleotide?
What type of reaction links these
together?
Nucleotides common
features
List the five nitrogenous bases found in
nucleotides.
Draw and label a simple diagram of a
nucleotide.
Joining nucleotides together
Which parts of two consecutive
nucleotides attach to each other?
What forms the backbone of a nucleic
acid?
Which groups will be left over at either end of the polymer?
From nucleotides to nucleic
acids
What is the identity of the sugar
molecule in DNA and RNA? DNA: RNA:
Organic bases are either Which bases are purines and which are Adenine: Cytosine: Uracil:
purines or pyrimidines pyrimidines? Thymine: Guanine:
2.1.16 DNA information storage
DNA is a stable
polynucleotide
How many polynucleotide strands create one DNA molecule?
What holds these polynucleotides together?
Why is it important that DNA is a stable molecule?
Hydrogen bonding
and base pairing getting it right
What does antiparallel mean?
What are the base pairing couplets in DNA?
Each polymer strand does not lie flat, but coils up into what
shape?
The two chains twist around each other, giving what final shape to a DNA molecule?
Making copies
Francis Crick, co-discoverer of DNA
Describe the sequence of events which occur when a DNA
molecule is replicated.
1)
2)
3)
4)
Why is DNA replication described as semi-conservative?
Which part of the DNA molecule contains the genetic code?
Fill in the sequence of bases which would be found on this
DNA strands complementary strand. T-T-C-C-G-A-C-A-G-T
If the top strands sugar-phosphate backbone runs from left to right, which way does the other ones run?
If 17% of a DNA molecules bases are thymine, what
percentage are cytosine?
2.1.17 Reading the instructions
RNA is different
Give two ways in which the structure
of RNA monomers differs from the structure of DNA monomers.
How is the structure of the final RNA molecule different to a DNA molecule?
The base-pairing rules apply
What are the base pairing couplets in
RNA?
Which base never appears in RNA?
Give the sequence of RNA bases that is complementary to this DNA strand.
DNA: A-T-T-A-G-A-C-C-G-T-G RNA:
Three forms of RNA What are the three types of RNA?
What are the instructions for?
What do the sequences of bases on
DNA code for?
What does the term gene mean?
Explain the functions of the three types of RNA in protein synthesis.
mRNA:
rRNA:
tRNA:
Place the following statements in the
order which correctly describes the
sequence of events which leads to protein synthesis.
1. An mRNA strand is formed through base pairing. 2. tRNA leaves the ribosome.
3. mRNA attaches to a ribosome.
4. The amino acid joins the growing polypeptide chain. 5. The gene for a particular protein is exposed.
6. The DNA double helix is unzipped.
7. The ribosome moves along the mRNA strand. 8. tRNA holding an amino acid attaches to the ribosome.
9. The new strand leaves the nucleus.
Quick quiz True or false?
1) Uracil is a purine. 4) Purines break down into uric acid, which causes gout.
2) Cytosine is complementary to guanine. 5) Nucleic acid bases always contain nitrogen. 3) The two strands of a DNA molecule are identical. 6) Ribose is a six carbon sugar.
2.1.18 Enzymes are globular proteins
All enzymes are proteins
Glyoxalase 1
A short recap: define the following terms.
Substrate:
Globular
Hydrophilic:
Secondary
Why are enzymes described as specific?
What feature of an enzyme allows it to bind to its substrate?
The active site is a tiny part
of an enzyme
What is the job of most amino acids in an enzyme?
What is an enzymes active site?
Catalysts in nature What is a catalyst?
Why are enzymes often used as industrial catalysts?
Substrate and product Write down a word equation for the reaction catalysed by
lactase.
?
2.1.19 Inside and out where enzymes work best
Organisms vary considerably What types of conditions might change
the shape of a protein?
Enzymes and endotherms Why is regulating body temperature worthwhile for birds and mammals?
Nutrition and digestion enzyme locations
What is a heterotroph?
What is the difference between intracellular and extracellular
enzymes?
Even autotrophs (organisms which dont need to digest) contain enzymes.
Why might this be?
Enzymes and protection
Why do white blood cells contain enzymes which can break down
substances?
What are white blood cells digestive enzymes contained in?
2.1.20 Enzyme action
Falling apart and staying
together
Draw a diagram showing the activation energy
for a reaction.
What is the reason for boiling non-reducing
sugars in acid, when testing for their presence?
How do enzymes increase the rate of a reaction?
From one stable molecule to
another Why do cells need enzymes in order to live?
Not just shape more about fit
Why is enzyme action compared to a lock and key?
What happens after the key has entered the
lock?
Holding it all together the induced fit hypothesis
Carbonic anhydrase, an enzyme in blood
How is the substrate held in place within the
active site?
What name is given to the enzyme while its
substrate is bound?
Why do the products leave the active site?
What is the name for this theory of enzyme
action?
A carbonic anhydrase molecule takes about one s (microsecond) to catalyse its reaction. How
many reactions would be catalysed per minute
by 1000 enzyme molecules?
2.1.21 Enzymes and temperature
Heat and kinetic energy
When a substance is heated, what
happens to the kinetic energy of its molecules?
What two effects does this have on collisions between molecules?
So what effect does heat have on
enzyme activity?
Heat, vibration, breaking
bonds and denaturation
Why can heat break bonds within an enzyme?
What happens if an enzymes bonds begin to break?
Why does this impair the enzymes
activity?
What is the name of this process?
Speeding up and slowing down optimum temperature
What is the meaning of the term optimum temperature?
In what type of habitat might an organism need enzymes with
particularly high optimum
temperatures?
How might those enzymes differ from
normal ones to cope with the
temperature?
On the reverse of this sheet, plot a graph using the data on the next page, and determine what the optimum temperature of this
enzyme is:
Temperature / C Rate of reaction / mol product
formed per minute
0 0
10 5
20 19
30 40
40 58
50 31
60 3
2.1.22 Enzymes at work pH effects
What is pH? What does pH measure?
What pH range is acidic?
pH and bonds
What are hydrogen ions attracted to?
How can hydrogen ions alter the shape of an enzyme?
pH and active sites How will hydrogen ions interfere with
substrate binding to the active site?
Optimum pH varies between enzymes
Why does a change from the optimum pH affect the rate of a reaction?
pH and location What is the optimum pH for the
enzyme pepsin?
A UV spectrometer can be used to measure the rate of a reaction. The products of some reactions absorb UV light by recording how quickly this absorbance changes, the spectrometer can calculate how quickly the concentration of the product is changing. This produces data like that in
the table to the left.
2.1.23 Enzymes at work concentration effects
Increasing the substrate concentration
In figure 1, why does increasing the
substrate concentration above a certain level no longer increase the
rate of reaction?
Why is it important to only record the initial rate of reaction?
Increasing the enzyme
concentration
Describe the sequence of events which
occurs when enzyme concentration is
increased for a fixed concentration of substrate.
1)
2)
3)
Initial reaction rate
What happens to the reaction rate as
the reaction proceeds?
When should the reaction rate be measured in order to give fair results?
Limiting factors Define the term limiting factor.
Enzyme and substrate
concentrations in cells
Why can enzymes be kept at much
lower concentrations than substrates?
How might a cell reduce an enzymes activity?
2.1.24 Enzymes at work inhibitors of action Inhibitors of enzyme-
controlled reactions What is an enzyme inhibitor?
Competitive inhibitors
Ampicillin is a competitive inhibitor
of bacterial enzymes
How do competitive inhibitors work?
How can competitive inhibition be overcome?
How does this work?
Non-competitive inhibitors
How do non-competitive inhibitors differ from competitive ones?
How do non-competitive inhibitors
reduce enzyme activity?
What effect will increasing the
substrate concentration have on the
rate of reaction?
How might you test whether an
inhibitor is competitive or non-competitive?
Why might non-competitive inhibitors
be deliberately produced by the cell?
Permanent inhibitors How do permanent inhibitors differ from reversible inhibitors?
2.1.25 Enzymes at work coenzymes and prosthetic groups
Enzymes shaping up
What is a cofactor?
What three types of cofactor exist?
Coenzymes
The iron-containing haem group is a
vital part of haemoglobin
Where do coenzymes bind to their enzyme?
How are coenzymes similar to
substrates?
How are coenzymes similar to
enzymes?
Why is vitamin B3 essential for human
health?
What is a prosthetic group?
What can prosthetic groups contribute to a protein?
Which metal ion is vital to the
function of carbonic anhydrase?
What is the purpose of the reaction catalysed by carbonic anhydrase?
How can inorganic ions affect reaction rates?
What two features of an enzyme can
inorganic ions affect?
Which halide ion is vital to the
function of amylase?
2.1.26 Interfering with enzymes poisons and drugs
Deadly poisons
Why is potassium cyanide deadly?
Would increasing the concentration of
oxygen a patient breathed save them from
cyanide poisoning? Explain your answer.
Replacement enzymes and cystic fibrosis
Why are enzyme tablets prescribed to cystic
fibrosis sufferers?
Why must these tablets resist acid?
Ethylene glycol poisoning
Ethanol and ethylene glycol.
Competitive inhibitors often have similar shapes to the substrates
they inhibit.
Where is ethylene glycol found?
Why is it dangerous?
What is given as a treatment for ethylene
glycol poisoning?
How does this help?
Snake venom an enzyme and
toxin cocktail
List four components of snake venom and explain how they help the snake kill its
prey.
1)
2)
3)
4)
Quick Quiz True or False?
1. Enzymes increase reaction rate by increasing the stability of the products. 2. Competitive inhibitors have a similar shape to an enzymes substrate. 3. Higher hydrogen ion concentration gives higher pH readings. 4. Increasing enzyme concentration increases reaction rate. 5. The pH of the human stomach is around 2. 6. Prosthetic groups are polypeptides. 7. Carbonic anhydrase converts CO2 to carbonic acid. 8. Heat is a measure of the kinetic energy of a substances molecules.
?
2.1.27 Investigating enzyme action 1
What can we investigate? How can you measure the rate of an
enzyme-catalysed reaction?
Dependent and independent
variables
What is the difference between
dependent and independent variables?
If you record the rate of a reaction at different pH levels, which variable is
dependent?
What can you do to the independent variable to increase the accuracy of
your results?
What needs to be controlled?
In an enzyme-catalysed reaction, which variables are particularly important to
control?
What is the best way to regulate temperature?
Why is using enzyme in living tissue
less accurate than using purified enzyme?
How can pH be regulated?
Timescales, rate and control
tests
Why might using high enzyme
concentrations make getting accurate
results difficult?
What is the relationship between time
and reaction rate?
Which variable always goes on the y-axis of a graph?
What is the purpose of a control test?
2.1.28 Investigating enzyme action 2
Following an enzyme-
controlled reaction
Why is it best to record the initial rate
of reaction?
How can you do this?
Sketch a graph and label it to show how you would measure the initial rate
of a reaction.
How do you calculate the gradient of a
tangent?
Examples of enzyme investigations
Write a method for an investigation
into the effect of pH on amylase
activity.
2.1.29 Enzymes and metabolism an overview
Catalytic power Why is it vital to control the power of enzymes?
Control of metabolic sequences
Explain how end-product inhibition works.
Some enzymes are crucial to
life
Why is ATP synthase vital for life?
Write a word equation for the conversion of ADP to ATP.
Inborn errors of metabolism
What is the cause of problems with the bodys proteins?
Which protein does not work correctly
in sufferers of phenylketonuria (PKU)?
If undiagnosed, what does this
condition lead to?
Phenylalanine is an essential amino acid. How might this affect the way
PKU sufferers are treated?
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