1 Biological Molecules EQs Flashcards
TOPIC 1
Compare and contrast the structure of starch
and the structure of cellulose (6 marks)
- Both polysaccharides
2.Both are glucose polymers
3.Both are made of glucose monomers;
- Both contain glycosidic bonds
- Both contain carbon, hydrogen and oxygen
- Starch made of α-glucose and cellulose made of β-glucose;
- Starch coiled and cellulose is straight
- Starch is branched and cellulose is unbranched
- Cellulose has (micro) fibrils and starch does not
- Starch has 1,6 glycosidic bonds and cellulose does not
- Starch contains two types of molecule and cellulose contains one type of molecule
- Starch is amylose and amylopectin and cellulose is one type of molecule
Describe how the structure of
glycogen is related to its
function (4 marks)
- Branched so compact;
- Polymer of glucose so easily hydrolysed;
- Branched so more ends for faster hydrolysis;
- Insoluble so does not affect water potential/osmosis
In humans, the enzyme maltase breaks down maltose to glucose. This takes place at normal body temp. Explain why maltase:
- only breaks down maltose
- allows this reaction to take place at normal body temp
(5 marks)
- tertiary structure
- active site complementary to maltose
- description of induced fit
- enzyme is a catalyst
- by forming enzyme-substrate complex
Compare and contrast the structure and properties of triglycerides and phospholipids (5 marks)
- Both contain ester bonds
- Both contain glycerol
- Both are insoluble in water
- T has three fatty acids and P has two fatty acids plus phosphate group
- T are hydrophobic and P has hydrophilic and hydrophobic regions
Describe how lactose is formed and where in the cell it would be attached to a polypeptide to form a glycoprotein (4 marks)
- Formed by glucose and galactose.
- Condensation reaction.
- Joined by glycosidic bond.
- Added to polypeptide in golgi.
Suggest how a student could measure the quantity of reducing sugar in a solution (2 marks)
- Filter + dry,
- find weight
Use of a colourimeter could improve repeatability of a student’s results. Give one reason why. (1 mark)
Quantitative, standardises the method
Describe a biochemical test to show that raffinose solution contains a non-reducing sugar. (3 marks)
- Heat with acid + neutralise,
- heat with benedict’s solution,
- red colour
Describe the chemical reactions involved in the conversions of polymers to monomers and monomers to polymers. Give two named examples of polymers and their associated monomers to illustrate your answer. (5 marks)
- Condensation joins monomers together, forms glycosidic bond and releases water
- Hydrolysis breaks a chemical bond between monomers and uses water
3 & 4. Examples: amino acid and protein, alpha glucose and starch, beta glucose and cellulose - Say bonds with your examples!
Describe two differences between the structure of a cellulose molecule and a glycogen molecule (2 marks)
- Cellulose= made of beta-glucose
Glycogen= made of alpha-glucose - Glycogen= 1,4 and 1,6 glycosidic bonds
Cellulose= 1,4 glycosidic bonds
Describe and explain two features of starch that makes it a good storage molecule (2 marks)
- Insoluble so doesn’t affect water potential
- Coiled so makes molecule compact
Describe the structure of glycogen (2 marks)
- Polysaccharide of alpha-glucose,
- branched
💫 Suggest how glycogen acts as a source of energy (2 marks)
- Hydrolysed to glucose,
- glucose used in respiration
Explain how cellulose molecules are adapted for their function in plant cells (3 marks)
- Long and straight chains,
- become linked together by many hydrogen bonds to form fibrils,
- provide strength to cell wall
Compare phospholipids and triglycerides (3 marks)
- Both have glycerol backbone
- Both contain elements C,H,O
- Both formed by condensation reactions
Describe how the structure of a protein depends on the amino acids it contains (5 marks)
- Structure is determined by position of amino acid / R group
- Primary structure is order of amino acids
- Secondary structure formed by hydrogen bonding
- Tertiary structure formed by interactions between R groups
- Creates active site in enzymes
- Quarternary structure formed by interactions between polypeptides
Cotton is a plant fibre used to make cloth. Explain how cellulose gives cotton its strength. (3 marks)
- Long, unbranched chains;
- Multiple chains lie side by side to form (micro)fibrils
- Hydrogen bonds holding chains together
Describe how a triglyceride molecule is formed. (3 marks)
- One glycerol and three fatty acids;
- Condensation reaction and removal of three molecules of water;
- Ester bonds formed
A fat substitute cannot be digested in the gut by lipase.
Suggest why. (2 marks)
- Fat substitute is not complementary
- Unable to bind to active site of lipase so no ES complex formed
Suggest why something cannot cross cell-surface membranes. (1 mark)
It is too large
Describe the induced-fit model of enzyme action and how an enzyme acts as a catalyst. (3 marks)
- Substrate binds to the active site
- The active site slightly changes shape so it is complementary to substrate
- This bends bonds, reducing activation energy;
A competitive inhibitor decreases the rate of an enzyme-controlled reaction.
Explain how. (3 marks)
- Inhibitor similar shape to substrate;
- Binds to active site;
- Prevents enzyme-substrate complex forming;
Explain how the active site of an enzyme causes a high rate of reaction. (3 marks)
- Lowers activation energy;
- Induced fit causes the active site to change shape;
- So enzyme-substrate complex causes bonds to form/break;
Formation of an enzyme-substrate complex increases the rate of reaction.
Explain how (2 marks)
- Reduces activation energy
- Due to bending bonds
Name the type of bond between:
1. complementary base pairs
2. adjacent nucleotides in a DNA strand (2 marks)
- hydrogen
- phosphodiester
Describe how a phosphodiester bond is formed between two nucleotides within a DNA
molecule. (2 marks)
- Condensation reaction
- Between phosphate and deoxyribose;
- Catalysed by DNA polymerase;
In the process of semi-conservative DNA replication, the two strands within a DNA
molecule are separated. Each then acts as a template for the formation of a new
complementary strand.
Describe how the separation of strands occurs. (2 marks)
- DNA helicase;
- Breaks hydrogen bonds between base pairs
Name the two scientists who proposed models of the chemical structure of DNA and of DNA replication (1 mark)
Watson and Crick
A scientist replicated DNA in a test tube. To do this, he mixed an enzyme with identical singlestranded DNA fragments and a solution containing DNA nucleotides.
Name the enzyme used in this DNA replication. (1 mark)
DNA polymerase
Use your knowledge of semi-conservative replication of DNA to suggest:
1. the role of the single-stranded DNA fragments
2. the role of the DNA nucleotides. (3 marks)
Role of single-stranded DNA fragments
1. Template;
2. Determines order of nucleotides
Role of DNA nucleotides
3. Forms complementary pairs
Describe the function of each of these enzymes.
DNA helicase
DNA polymerase (2 marks)
DNA helicase – unwinding DNA and breaking hydrogen
bonds between strands
DNA polymerase – joins adjacent nucleotides and forms phosphodiester bond
Contrast the structures of ATP and a nucleotide found in DNA to give two differences. (2 marks)
- ATP has ribose and DNA nucleotide has deoxyribose;
- ATP has 3 phosphates and DNA nucleotide has 1
phosphate - ATP base always adenine and in DNA nucleotide base can
be different
💫 Describe how an ATP molecule is formed from its component molecules. (4 marks)
- adenine, ribose,
three phosphates - ADP + Pi
- Condensation reaction
- ATP synthase
State and explain the property of water that can help to buffer changes in temperature. (2 marks)
- Water has a high specific heat capacity;
- Can gain / lose a lot of energy without changing temperature;
Describe the process of semi-conservative replication of DNA. (5 marks)
- DNA helicase unwinds DNA and breaks hydrogen bonds;
- Both strands act as templates
- Nucleotides line up in complementary pairs
- DNA polymerase joins adjacent nucleotides
- Forming phosphodiester bonds
- Each new DNA molecule consists of one original strand and one new strand;
Explain five properties that make water important for organisms. (5 marks)
- A metabolite in respiration
- A solvent so metabolic reactions can occur
- High specific heat capacity so buffers changes in temperature
- Large latent heat of vaporisation so provides a cooling effect through evaporation
- Cohesion between water molecules so supports columns of water in plants
Use your knowledge of water potential to suggest why lactulose can be used to help
people suffering from constipation. (2 marks)
- Lactulose lowers the water potential of faeces
- Water enters due to osmosis and softens the faeces
Describe how a peptide bond is formed between two amino acids to form a
dipeptide. (2 marks)
- Condensation reaction
- Between amine and carboxyl
The secondary structure of a polypeptide is produced by bonds between amino
acids.
Describe how. (2 marks)
- Hydrogen bonds;
- Forming β pleated sheets / α helix;
💫 Two proteins have the same number and type of amino acids but different tertiary
structures.
Explain why. (2 marks)
- Different primary structure;
- Forms ionic / hydrogen / disulfide bonds in different places;
Describe the structure of proteins. (5 marks)
- Polymer of amino acids;
- Joined by peptide bonds;
- Formed by condensation;
- Primary structure is order of amino acids;
- Secondary structure is folding of polypeptide chain due to hydrogen bonding;
- Tertiary structure is 3-D folding due to hydrogen bonding and ionic / disulfide bonds;
- Quaternary structure is two or more polypeptide chains.
A polypeptide has 51 amino acids in its primary structure.
What is the minimum number of DNA bases required to code for the amino
acids in this polypeptide? (1 mark)
153
A high concentration of galactose slows down the breakdown of lactose by lactase.
Use your knowledge of competitive inhibition to suggest why. (2 marks)
- Galactose is a similar shape to lactose
- Galactose binds with active site
- Fewer or no E-S complexes;
Sucrase does not hydrolyse lactose. Use your knowledge of the way in which
enzymes work to explain why. (2 marks)
- Lactose has a different shape / structure;
- Does not bind to active site of sucrase;
💫 Explain how digestion of starch in the gut (small intestine) leads to an increase in the concentration of glucose in the blood. Details of co-transport are not required. (3 marks)
- Hydrolysed by amylase /
maltase; - Produces glucose (in the gut);
- Small enough to cross the gut wall into the blood
Suggest a method you could use to estimate the concentration of glucose in several different solutions that all turned brick red with Benedict’s reagent in 3 minutes. (1 mark)
- Time how long it takes to go brick red;
- Weigh precipitate;
- Use smaller volume of glucose samples
Hydrogen bonds are important in cellulose molecules. Explain why. (2 marks)
- Forms microfibrils, providing
strength - Hydrogen bonds strong in large numbers
Amylase digests starch. Suggest an experiment to test if all of amylase had been inhibited (2 marks)
- Add Benedict’s reagent and heat
- If all amylase had been inhibited then the solution would remain blue
What is a pH buffer? (1 mark)
keeps the pH constant
Suggest one advantage of using a pH meter rather than a pH indicator? (1 mark)
pH meter has greater accuracy because pH indicator provides a colour and colour change is subjective
💫 In an experiment on hydrolysis of triglycerides, explain why the pH decreases when the lipase is added to the milk? (1 mark)
fatty acids produced
In an experiment on hydrolysis of triglycerides, suggest why the pH remained constant after 2 minutes? (2 marks)
- No more fatty acids produced
- All triglycerides used up
Describe how a scientist would have produced a calibration curve on the concentration of maltose? (3 marks)
- Make maltose solutions of known concentrations (and carry out quantitative Benedict’s test on each)
- Use colorimeter to measure colour of each solution and plot calibration curve
- Find concentration of sample from calibration curve
💫 Suggest how one protein can be the substrate to two enzymes? (2 marks)
- Different parts of protein
- Each enzyme is specific to a different part
When bread becomes stale, the structure of some of the starch is changed. This changed starch is called retrograded starch.
Scientists have suggested retrograded starch is a competitive inhibitor of
amylase in the small intestine.
Assuming the scientists are correct, suggest how eating stale bread could
help to reduce weight gain. (3 marks)
- Less hydrolysis of starch;
- To maltose;
- So less absorption of glucose
Describe how amino acids join to form a polypeptide so there is always NH2 at one end and COOH at the other end. (2 marks)
- NH2 group joins to a COOH group to form a
peptide bond; - (So in chain) there is a free NH2 group at one end
and a free COOH group at the other
Describe two other ways in which all dipeptides are similar and one way in
which they might differ. (3 marks)
Similarity
1. Amine group
2. Carboxyl group
3. Two R groups
4. All contain C,H,N,O
Difference
1. Different R groups
Lyxose binds to the enzyme.
Suggest a reason why the rate of reaction increases with lyxose? (3 marks)
- Binding alters the tertiary structure of the enzyme
- This causes active site to change shape
- So more successful E-S complexes form per minute
Explain why DNA strands run in opposite directions (4 marks)
- DNA has antiparallel strands
- shape of the nucleotides is different
- Enzymes have active sites with specific shape;
- Only bind with substrates with complementary shape
Explain why ATP causes muscle contraction? (2 marks)
- More ATP hydrolysed by ATP hydrolase
- so more energy
released, so more muscle contraction
Give two ways in
which ATP is a suitable energy source for cells to use. (2 marks)
- Releases relatively small amount of energy
- Releases energy instantaneously
Give two ways in which the hydrolysis of ATP is used in cells. (2 marks)
- To provide energy for other reactions/named process;
- To add phosphate to other substances and make them more reactive/change their shape;
Give two properties of water that are important in the cytoplasm of cells. For each property of water, explain its importance in the cytoplasm. (4 marks)
- Polar molecule;
- Acts as a universal solvent;
- Universal solvent;
- Metabolic reactions occur faster in solution;
Explain why phospholipids can form a bilayer but triglycerides cannot (3 marks)
- Phospholipid both hydrophobic and hydrophilic
- Triglycerides only hydrophobic
- Hydrophilic attracts water (to
either side of bilayer);
Use your knowledge of lipid digestion to explain an increase in concentration of fatty acids but a decrease in concentration of triglycerides (3 marks)
- Triglycerides decrease because of the action of
lipase
OR
Fatty acids increase because of the action of
lipase; - Triglycerides decrease because of hydrolysis of
triglycerides
OR
Fatty acids increase because of hydrolysis of
triglycerides - Triglycerides decrease because of digestion of
ester bonds between fatty acid and glycerol
OR
Fatty acids increase because of digestion of ester bonds between fatty acid and glycerol
Explain the function of ATP hydrolase in co-transport? (2 marks)
- (ATP to ADP + Pi ) Releases energy;
- energy allows ions to be moved against a
concentration gradient
After collecting enzyme samples, why would you immediately heat them to
70 °C for 10 minutes? (2 marks)
- To denature the enzymes
- So no further digestion/hydrolysis
occurred
Describe how an enzyme can be phosphorylated. (2 marks)
- Attachment of inorganic phosphate to the enzyme
- Released from hydrolysis of ATP
Describe the structure of DNA (5 marks)
- Polymer of nucleotides;
- Each nucleotide formed from deoxyribose, a phosphate group and a nitrogenous base;
- Phosphodiester bonds between nucleotides
- Double helix held by hydrogen bonds;
- Hydrogen bonds between adenine, thymine
and cytosine, guanine;
Some people cannot digest lactose when they are adult. They could digest lactose
when they were children.
Use your knowledge of water potential to explain why these adults get diarrhoea when
they drink milk. (2 marks)
- Low(er) water potential in lumen
- Water enters lumen by osmosis;
What reducing sugar, or sugars, would you expect to be produced during chewing?
Give a reason for your answer. (2 marks)
- Maltose;
- Salivary amylase breaks down starch.
Why would samples be mixed with water, hydrochloric acid and pepsin? (1 mark)
mimics effect of stomach
In the control experiments, cooked wheat was chopped up to copy the effect of
chewing.
Suggest a more appropriate control experiment. Explain your suggestion. (2 marks)
- Add boiled saliva;
- Everything same as experiment but salivary amylase denatured.
The lactose-free milk made after hydrolysis with lactase tastes sweeter than the
cow’s milk containing lactose.
Suggest why. (2 marks)
- Lactose hydrolysed to galactose and glucose;
- So more sugar molecules;
Suggest two reasons why they chose to use cats as
model organisms. (2 marks)
- mammals so have same reaction as humans
- can use a large number
Explain why monitoring the pH of the mixture could show whether the cat’s milk
contained lipase. (2 marks)
- Hydrolysis of lipids produces fatty acids;
- Which lower pH of mixture.
Explain two ways in which fatty acids are important in
the formation of new cells. (4 marks)
- Fatty acids used to make phospholipids, phospholipids in membranes;
- More phospholipids more membranes made;
- Fatty acids respired to release energy, more triglycerides more energy released;
- Energy used for cell production
Humans and grasshoppers have very similar percentages of each base in
their DNA but they are very different organisms.
Use your knowledge of DNA structure and function to explain how this is
possible. (2 marks)
- Have different genes
- So bases are in a different sequence
- So different amino acid sequence
Humans synthesise more than their body mass of ATP each day. Explain why it is
necessary for them to synthesise such a large amount of ATP. (2 marks)
- ATP is an immediate source of energy;
- ATP only releases a small amount of energy at a time;
Why was the solution in which the mitochondria were suspended isotonic? (1 mark)
Prevent damage to mitochondria caused by osmosis
