B1 Biological molecules Flashcards
- what is covalent bonding
when atoms share their electrons to fill their outer shells
- what is ionic bonding
ions with opposite charges attract one another
electrons are transferred from one ion to another
- what is hydrogen bonding
a weak electrostatic attraction between the negative part of one polarised molecule and the positive part of another
- what is a monomer
monomers are smaller repeating subunits from which polymers are made
- what is a polymer
polymers are molecules made from a large number of repeating monomers joined together
- explain how polymers are formed
monomers join together in a condensation reaction
a bond is formed
water is removed
- explain how are polymers broken down
polymers are hydrolysed into monomers
a bond is broken
water is used
- Describe the chemical reactions involved in the conversion of polymers to monomers and monomers to polymers.
Give two named examples of polymers and their associated monomers to illustrate your answer.
- A condensation reaction joins monomers together and forms a (chemical) bond and releases water;
- A hydrolysis reaction breaks a (chemical) bond between monomers and uses water;
- A suitable example of polymers and the monomers from which they are made;
- A second suitable example of polymers and the monomers from which they are made;
- Reference to a correct bond within a named polymer;
- Identify polymers of the following monomers, and the bonds formed between them in polymerisation – amino acids, alpha glucose, beta glucose, nucleotides
Amino acids – polypeptide – peptide bonds
Alpha glucose – starch – glycosidic bonds
Beta glucose – cellulose – glycosidic bonds
Nucleotides – polynucleotides (DNA and RNA) – phosphodiester bonds
- reaction that joins two monomers together
condensation
- reaction that breaks bonds between monomers
hydrolysis
- what type of carbohydrate are glucose galactose and fructose
monosaccharides
- what is the general formula for a monosaccharide
(CH2O)n
n is any number from 3 - 7
- what type of molecules are sucrose, lactose and maltose
disaccharides
15a. what monomers make up sucrose
glucose and fructose
15b. what monomers make up lactose
glucose and galactose
15c. what monomers make up maltose
glucose and glucose
16.what do we call a molecule that consists of two monosaccharides
disaccharide
- what do we call a molecule that consists of many monosaccharides bonded together
polysaccharide
- what are isomers
molecules with same molecular formula but different molecular structure
- alpha glucose
two H is on top
- beta glucose
H top left and bottom right
- Identify one similarity and one difference between glycogen and starch.
Similarity – both insoluble polysaccharides formed by condensation reaction of alpha glucose.
Both are branched molecules.
Difference – glycogen is more branched.
- Identify two differences between starch and cellulose.
Starch is made from alpha glucose monomers and cellulose beta glucose.
Starch is branched and cellulose is in straight chains.
Starch does not contain hydrogen bonds but cellulose does.
- Explain the role of starch in plants?
Energy store in plants
Can be hydrolysed into glucose for respiration
- Explain the role of cellulose in plants?
Found in cell wall of plants
Provides structure and support
- Explain the role of glycogen in animals?
Energy store in animals
Can be hydrolysed into glucose for respiration
- Describe how the structures of starch and cellulose molecules are related to their functions
Starch
1. Helical/ spiral shape so compact;
2. Large and insoluble so osmotically inactive;
3. Branched so glucose is easily released for respiration;
4. Large and insoluble molecule so cannot leave cell
Cellulose
5. Long, straight, unbranched chains of β glucose;
6. Joined by hydrogen bonding;
7. To form microfibrils;
8. Provides rigidity and strength;
Add Benedict’s solution and heat. If sugar present then colour changes from blue, green, yellow, orange, brick red.
- Describe the test for a reducing sugar?
Add Benedict’s solution and heat.
If sugar present then colour changes from blue to brick red.
- What is a reducing sugar?
sugar that donates electrons
- Describe the test for a non-reducing sugar
Add Benedicts and heat.
If it remains blue, boil new sample with HCl to hydrolyse the glycosidic bonds
Then neutralise with sodium hydrogen carbonate. Add Benedict’s and heat.
If sugar present then colour changes from blue, green, yellow, orange, brick red.
- Describe the test for starch?
Add iodine in potassium iodide solution
Positive result = yellow to blue/black
- What type of bond joins the monomers on carbohydrates?
glycosidic bonds
- What type of biological molecule are triglycerides?
lipids
- What are triglycerides made of?
glycerol and 3 fatty acids
- What type of bond joins the components of a triglyceride?
ester
- state 5 main roles of lipids
Phospholipid bilayer in cell membranes
Energy source
Waterproofing
Insulation
Protection
- Compare and contrast the structure and properties of triglycerides and phospholipids
- Both contain ester bonds between glycerol and fatty acid;
- Both contain glycerol;
- Fatty acids on both may be saturated or unsaturated;
- Both are insoluble in water;
- Both contain C, H and O but phospholipids also contain P;
- Triglyceride has three fatty acids and phospholipid has two fatty acids plus phosphate group;
- Triglycerides are hydrophobic/non-polar and phospholipids have hydrophilic and hydrophobic region;
- Phospholipids form monolayer/micelle/bilayer in water but triglycerides don’t;
- What is the difference between a saturated and an unsaturated fatty acid?
Saturated has no C=C double bonds but unsaturated does.
- Why do lipids not affect water potential?
large and insoluble
- Explain why lipids are important for animals living in dry environments?
High ratio of hydrogen to oxygen atoms
So can release water
- Why is a low mass to energy ratio in triglycerides useful to organisms?
Good storage molecule
Because much energy can be stored in a small volume
- What is the difference between a triglyceride and a phospholipid?
Triglyceride is made of glycerol attached to 3 fatty acids
Phospholipids one of the fatty acids is substituted by a phosphate – containing group.
- Describe how you could test a sample for the presence of lipid
If solid then grind first
Mix with ethanol
Pour onto water
A milky/ white emulsion indicates a positive result for lipids
- Draw and label the structure of an amino acid
H
I
NH2 —— C —— COOH
I
R
NH2 - amine group
COOH - carboxylate group
R - side chain
- How many amino acids are there
20
- What do you call two amino acids bonded together
dipeptide
- How do dipeptides differ
Type of amino acids they contain
Variable/different R group(s)
- How are dipeptides similar
Amine/NH2 (group at end)
Carboxyl/COOH (group at end)
Two R groups
All contain C and H and N and O
- What would you call many amino acids bonded together?
polypeptide
- What type of bond joins two amino acids bonded together
peptide
- What is the primary structure of proteins
sequence of amino acids
5q. What is the secondary structure of proteins
folding
due to hydrogen bonds
of polypeptide chain
into alpha helix or beta pleated sheets
- What is the tertiary structure of a protein
overall 3D shape due to further folding
- Name 3 types of bond that hold the tertiary structure of a protein
ionic, hydrogen and disulphide bonds
- describe the structure of proteins
- Polymer of amino acids;
- Joined by peptide bonds;
- Formed by condensation;
- Primary structure is order of amino acids;
- Secondary structure is folding in alpha helix and or beta pleated sheets 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.
- Describe the biochemical tests you would use to confirm the presence of lipid, non-reducing sugar and amylase in a sample.
Lipid
1. Add ethanol/alcohol then add water and shake/mix
OR
Add ethanol/alcohol and shake/mix then pour into/add water;
2. White/milky emulsion
OR
emulsion test turns white/milky;
Non-reducing sugar
3. Do Benedict’s test and stays blue/negative;
4. Boil with acid then neutralise with alkali;
5. Heat with Benedict’s and becomes red/orange (precipitate);
Amylase
6. Add biuret (reagent) and becomes purple/violet/mauve/lilac;
7. Add starch, (leave for a time), test for reducing sugar/absence of starch;
- Name the two scientists who proposed models of the chemical structure of DNA and of DNA replication
Watson and Crick
- Draw and label a nucleotide
pentose sugar - deoxyribose
phosphate group
nitrogenous organic bases - ATCG
- What are the components of a DNA nucleotide?
Phosphate group
Deoxyribose sugar
Bases – adenine, thymine, cytosine and guanine
- What are the components of an RNA nucleotide?
Phosphate group
Ribose sugar
Bases – adenine, uracil, cytosine and guanine
- What type of bond joins two nucleotides?
phosphodiester
- Which bases join together by complimentary base pairing?
Adenine – thymine.
Cytosine – guanine.
- What type of bond forms between two complimentary bases?
hydrogen
- Explain how the structure of DNA is related to its functions.
- Sugar-phosphate backbone/ helix so provides strength/ protects bases / protects hydrogen bonds;
- Long / large molecule so can store lots of information;
- Helix / coiled so compact;
- Base sequence codes for amino acids / protein;
- Double stranded so accurate replication can occur by semi-conservatively
- Weak hydrogen bonds for replication / strand separation
- Many hydrogen bonds so stable and strong;
- Identify four differences between RNA and DNA
DNA contains deoxyribose sugar and RNA contains ribose sugar.
DNA contains thymine and RNA contains uracil.
DNA is double stranded and RNA is single stranded.
RNA is shorter than DNA.
- Explain semi-conservative replication
One strand acts as a template
Each new DNA molecule contains one original strand and one new strand
- Who were the 2 scientists that designed an experiment that proved DNA replication was semi-conservative?
Meselsohn and Stahl
- What 3 facts did Meselsohn and Stahl base their experiment on?
All the bases in DNA contained nitrogen
Nitrogen has 2 isotopes – 14N and 15N
Bacteria will incorporate nitrogen form their growing medium into new DNA that they make
- If the DNA in a bacterial culture contains 14N but it grown in a medium containing 15N, why does the second generation have a mixture of 14N and 15N in its DNA?
Each new DNA molecule in the second generation contains one new strand containing 15N and one old strand containing 14N
- Describe the role of two named enzymes in the process of semi-conservative replication of DNA.
- DNA helicase causes breaking of hydrogen between DNA strands;
- DNA polymerase joins the DNA nucleotides;
- Forming phosphodiester bonds;
- Why does each strand of DNA get copied in opposite directions?
DNA has antiparallel strands
Shape of the nucleotides is different at the 5’ and the 3’ end
DNA polymerase has an active sites with a specific shape
Only the 3’ end can bind with the active site of DNA polymerase
- What is ATP made of
adenine
ribose
3 phosphates
- What role does ATP play in cells?
The hydrolysis of ATP provides energy for energy-requiring reactions.
The inorganic phosphate released can be used to phosphorylate other compounds, making them more reactive
- Write an equation showing the hydrolysis of ATP
ATP + (H2O) → ADP + Pi.
- What enzyme catalyses the hydrolysis of ATP?
ATP hydrolase
- Write an equation showing the condensation of ADP and Pi
ADP + Pi → ATP + (H2O)
- What enzyme catalyses the condensation of ATP?
ATP synthase
- Explain why ATP better than glucose as an energy source?
Each ATP release less energy than a glucose molecule so is released in small manageable amounts
Hydrolysis of ATP is a single reaction and therefore an immediate energy source
- Describe 5 uses for ATP in organisms
Metabolic processes, such as making polymers from monomers
Muscle contraction for movement
Active transport to move molecules or ions against their concentration gradient
Secretion where lysosomes are made to aid movement of products out of the cell
Activation of molecules – phosphorylation by addition of Pi makes molecules more reactive
Lowers the activation energy of the reaction it catalyses.
- How do both enzymes and catalysts speed up chemical reactions?
Lowers the activation energy of the reaction it catalyses.
- Explain how the active site of an enzyme causes a high rate of reaction.
Lowers the activation energy of the reaction it catalyses.
Lowers activation energy;
Induced fit causes active site (of enzyme) to change shape
(So) enzyme-substrate complex causes bonds to form/break
- Explain why an enzyme can only catalyse one particular reaction.
Each enzyme has a unique tertiary structure.
Therefore shape of the active site is complimentary to one substrate
Therefore specific for only one substrate
- What needs to happen in order for an enzyme to catalyse a reaction?
Substrate needs to attach to the active site of the enzyme
This causes the enzyme to change shape and mold itself around the substrate
- Explain the effect of low temperatures of the rate of enzyme activity?
Enzymes and substrates have less kinetic energy
Therefore fewer successful collisions between them
So fewer enzyme-substrate complexes formed
So lower rate of reaction
- Explain the effect of very high temperatures on the rate of enzyme activity?
Bonds holding the tertiary structure break due to heat
Active site denatures and irreversible changes shape
Substrate can no longer fit active site
Fewer enzyme-substrate complexes formed
Lower rate of reaction
- Why would a change in pH slow the rate of enzyme activity?
H+ and OH- ions in acidic or alkaline solutions interfere with the ionic bonds in the tertiary structure
Active site changes shape and no longer complimentary for substrate
Fewer enzyme-substrate complexes formed
So lower rate of reaction
- Draw a sketch graph to show the effect of substrate concentration on enzyme activity
rate if reaction - y axis
substrate conc - x axis
increasing curved line
- Describe and explain the effect of increasing substrate concentration on the rate of an enzyme controlled reaction
Increasing substrate conc increases the rate of reaction
Because more substrate molecules colliding with enzyme molecules
After a certain conc, any increase will have no effect on the rate of reaction
Since substrate conc no longer the limiting factor
Active sites become saturated/ all active sites are in use
And are working at their maximum rate
- Draw a sketch graph to show the effect of enzyme concentration on enzyme activity
rate if reaction - y axis
enzyme conc - x axis
increasing curved line
- Describe and explain the effect of increasing enzyme concentration on the rate of an enzyme controlled reaction
Increasing enzyme conc will increase rate of reaction
As more active sites are available for substrates to collide with
After a certain concentration the enzyme conc is no longer the limiting factor
So the rate plateaus
- Describe the lock and key model of enzyme activity
Enzymes active site like a lock and the substrate like a key.
Each substrate is a perfect fit for the enzymes active site like a key is a perfect fit for each lock.
- Explain how the induced fit model is a more realistic model of enzymes
Enzymes active site is complimentary to the substrate but not perfect. As substrate moves into active site, enzyme moulds itself around substrate weakening the bonds in the substrate.
This is likely to be the reason the activation energy is lowered.
- Explain what a competitive inhibitor does?
Similar shape to the substrate so fits into active site
Fewer enzymes-substrate complexes formed.
- How could you overcome the effect of a competitive inhibitor?
Add more substrate and eventually the substrate will out compete the competitive inhibitor.
- Describe competitive and non-competitive inhibition of an enzyme.
- Inhibitors reduce binding of enzyme to substrate / prevent formation of ES complex;
(Competitive inhibition), - Inhibitor similar shape (idea) to substrate;
- (Binds) in to active site (of enzyme);
- (Inhibition) can be overcome by more substrate;
(Non-competitive inhibition), - Inhibitor binds to site on enzyme other than active site;
- Prevents formation of active site / changes (shape of) active site;
- Cannot be overcome by adding more substrate;
- Describe competitive and non-competitive inhibition of an enzyme.
- Inhibitors reduce binding of enzyme to substrate / prevent formation of ES complex;
(Competitive inhibition), - Inhibitor similar shape (idea) to substrate;
- (Binds) in to active site (of enzyme);
- (Inhibition) can be overcome by more substrate;
(Non-competitive inhibition), - Inhibitor binds to site on enzyme other than active site;
- Prevents formation of active site / changes (shape of) active site;
- Cannot be overcome by adding more substrate;
- Explain what a non-competitive inhibitor does?
Not a similar shape to active site but attaches to another part of the enzyme (allosteric site).
This causes active site be distorted
So fewer enzyme-substrate complexes formed.
- Describe how a non-competitive inhibitor can reduce the rate of an
enzyme - controlled reaction.
- Attaches to the enzyme at a site other than the active site;
- Changes (shape of) active site
- (So active site and substrate) no longer complementary so less/no substrate can fit/bind;
- What is the role of DNA helicase and DNA polymerase?
DNA helicase breaks hydrogen bonds
DNA polymerase joins adjacent nucleotides together
- What is the role of ATP synthase in photosynthesis and respiration?
Re-synthesises ATP by the condensation and ADP and Pi.
- Describe the roles of iron ions, sodium ions, and phosphate ions in cells.
Iron ions
1. Haemoglobin binds/associates with oxygen
OR
Haemoglobin transports/loads oxygen;
Sodium ions
2. Co-transport of glucose/amino acids (into cells);
3. (Because) sodium moved out by active transport/Na – K pump;
4. Creates a sodium concentration/diffusion gradient;
5. Affects osmosis/water potential;
Phosphate ions
6. Affects osmosis/water potential;
7. Joins nucleotides/in phosphodiester bond/in backbone of DNA/RNA/in nucleotides;
8. Used in/to produce ATP;
9. Phosphorylates other compounds (usually) making them more reactive;
10. Hydrophilic/water soluble part of phospholipid bilayer/membrane;
- Explain six properties that make water important for organisms.
- A metabolite in condensation/hydrolysis/ photosynthesis/respiration;
- A solvent so (metabolic) reactions can occur
OR
A solvent so allowing transport of substances; - High 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);
- Cohesion (between water molecules) so produces surface tension supporting (small) organisms;
