Section 1- Biological molecules Flashcards
What is a monomer?
Smaller units from which larger molecules are made.
What are polymers?
Molecules made from a larger number of monomers joined together.
What is polymerisation?
Process by which polymers are formed by monomers.
What is a condensation reaction?
Where 2 molecules are joined together forming a chemical bond with the elimination of water.
What is a hydrolysis reaction?
Breaks chemical bond between two molecules and involves the use of water.
What are the 3 types of monosaccharide?
Glucose
Fructose
Galactose
What does GLUCOSE + GLUCOSE form?
MALTOSE + water
What does GLUCOSE + FRUCTOSE form?
SUCROSE + water
What does GLUCOSE + GALACTOSE form?
LACTOSE + water
What bond form between disaccharide?
Glyosidic bond
What reaction occurs to join monosaccharides?
Condensation reaction
What are the 3 polysaccharides?
Starch
Cellulose
Glycogen
What are features of starch?
Alpha glucose
Plant energy storage
Branched: amylopectin
Unbranched: amylose
Insoluble
Compact
What are features of glycogen?
Alpha glucose
Animal energy storage
Short chains
Highly branched
Insoluble
Compact
What are features of cellulose?
Beta glucose
Straight, unbranched chains running parallel
Linked by hydrogen bonds
Plant cell wall- provides rigidity
Microfibrils- Macrofibrils- Fibres
What reaction occurs for polysaccharides and what bond?
Condensation reaction
Glyosidic bond
What are the 5 reducing sugars?
Glucose Galactose Fructose Lactose Maltose
How do you conduct the Benedict’s test?
- Add Benedict’s solution to sample
- Heat it
- Spectrum of colours
Positive= Brick red Negative= Blue
What is the non-reducing sugar?
Sucrose
How do you test for non-reducing sugar?
- Add Hydrochloric acid and heat it
(to hydrolyse non-reducing) - Neutralise solution using sodium hydrogen carbonate
- Add Benedict’s solution and heat
- Spectrum of colours
Positive= Brick red
Negative= Blue
What are the roles of lipids?
- Source of energy
- Waterproofing
- Insulation
- Protection
What are triglycerides made up of?
Glycerol
3x fatty acid
How are triglycerides formed?
- Condensation reaction
- Formation of 3 water molecules
- Ester bond
What are saturated fatty acids?
No double carbon bonds between carbon atoms
What are mono-unsaturated fatty acids?
One double bond between carbon atoms
What are poly-unsaturated fatty acids?
More than one double bond between carbon atoms
What is the advantage on an insect polymerising sugars into polysaccharides?
Polysaccharides are insoluble
Do not affect water potential
How can the active site of an enzyme cause a high rate of reaction?
Induced fit: active site changes shape when substrate collides
Enzyme lowers activation energy
Enzyme-substrate complex causes bonds to form/ break
How does a non-competitive inhibitor reduce the rate of an enzyme-controlled reaction?
Inhibitor binds to allosteric site
Active site has changed shape
Active site and substrate no longer complementary so less substrate can fit
How do you test for amylase?
Add Biuret solution, becomes purple
Add starch to test for reducing sugar
Why do large molecules often contain carbon?
Carbon atoms readily link to one another to form a chain
What is the name for a molecule that is make up of many similar repeating units?
Polymer
Why does Benedict’s reagent turn red when heated with a reducing sugar?
Sugar donated electrons that reduce blue copper sulphate to orange copper oxide
How does the structure of triglycerides relate to their properties?
Non-polar molecules = insoluble in water
High ratio energy-storing carbon-hydrogen bonds to carbon atoms = good source of energy
Low mass: energy ratio = good storage molecule
High ratio of hydrogen : oxygen atoms, release water when oxidised = source of water
How does the structure of phospholipids relate to their properites?
- Polar molecules = form bilayer
- Hydrophilic heads help to hold at surface of membrane
- Phospholipid structure allows them to form glycolipids = important in cell recognition
How do you test for proteins?
Biuret test which detects peptide bond:
- Place sample in sodium hydroxide
- Add copper sulfate solution and mix
- Purple colour indicates presence of peptide bond
What is the semi-conservative model in DNA replication?
Original DNA molecule split into 2 separate strands
Strands acted as templates
1 old strand, 1 new strand
Who proposed evidence for the semi-conservative model?
Watson and Crick
What was the Meselon and Stahl experiment in semi-conservative replication?
Using 2 isotopes of nitrogen - heavy nitrogen 15N and light 14N
- Grew E.coli for several generations in each isotope
- Cells harvested, DNA isolated, centrifuged.
- DNA formed separate bands according to densities. - E.coli from 15N moved with 14N
After 1 generation band in between space formed
What is the covalent chemical bond which links 2 amino acids?
Disulphide bridge
What is a visible similarity between fructose and a-glucose?
Both C6H12O6
What does hydrophilic mean?
Interacts and is attracted to water
What does hydrophobic mean?
Orients itself away from water
What 2 parts is a phospholipid made up of?
Hydrophilic head
Hydrophobic tail
How do you test for lipids?
Emulsion test:
- Add ethanol to sample
- Shake thoroughly
- Add water and shake again
- Milky-white emulsion indicated presence of lipid.
What would be a suitable control test for the emulsion test?
Repeat test but use water instead of sample.
Final solution should remain clear.
Why does the cloudy white colour form when testing for a lipid?
Lipid in sample being finely dispersed in water to form an emulsion.
Light passing through emulsion is refracted as it passes from oil droplets to water droplets, appearing cloudy.
What are the 4 chemical groups in an amino acid?
Amino group
Carboxyl group
Hydrogen atom
R group
How does amino acids form?
Condensation reaction
Combining OH from carboxyl group and H from amino group of another amino acid.
What is the link between 2 amino acids called?
Peptide bond
Between carbon atoms and nitrogen atom
What is the primary structure of a protein?
Sequence, type, number of amino acids
What is the secondary structure of a protein?
Weak hydrogen bonds form.
Causing alpha helix or beta pleated sheet.
What is the tertiary structure of a protein?
Bonds formed between twisting a-helix:
Disulfide bridges- strong
Ionic bonds- broken by change in pH
Hydrogen bonds- easily broken
What is the quaternary structure of a protein?
More than one polypeptide chain.
linked in various ways
What is the structure and function of fibrous proteins?
Can form long chains/ fibres
Insoluble in water
Useful for structure and support
What is the structure and function of globular proteins?
Spherical and compact
Carry out metabolic functions (enzymes)
What is the activation energy?
The minimum amount of energy needed to activate the reaction.
What is the induced fit model of enzyme action?
Enzyme is flexible and can mould itself around substrate.
Enzyme alters shape in presence of substrate.
How is the activation energy lowered using the induced fit model?
When enzyme changes shape, strain is put on substrate molecule.
Stain distorts a particular bond and lowers activation energy needed to break bond.
Why are enzymes effective in tiny quantities?
They are not used up in the reaction and so can be used repeatdly.
Why would changing one amino acid in the active site prevent the enzyme from functioning?
Changed amino acid may no longer bind to substrate.
Why would changing certain amino acids that are not part of the active site also prevent the enzyme from functioning?
Changed amino acid may be one that forms hydrogen bond with other amino acids.
Could cause change in tertiary structure if hydrogen bond does not form.
What is the effect of temperature on enzyme action?
Increases kinetic energy
More collisions due to more rapid movement
Too high:
Enzyme denatures, break in hydrogen bonds
Change in tertiary structure/ active site
Rate decreases
What is the effect of pH on enzyme action?
Away from optimum:
Change in pH alters charges on amino acids
Causes bonds in tertiary structure to break
Changes active site
What is the effect of enzyme concentration on the rate of reaction?
If substrate is limiting:
rate will stabilise to constant
All available substrate is already being used
If substrate is excess:
increase in rate of reaction
What is the effect of substrate concentration on the rate of enzyme action?
If enzyme is limiting:
Rate will stabilise to constant
All available substrate is already being used
If enzyme is excess:
Increase in rate of reaction
What are competitive inhibitors?
Bind to the active site of an enzyme
Inhibitor has complementary shape to active site
Compete with substrate for active site
Inhibitor is not permanent
What are non-competitive inhibitors?
Bind to allosteric site of enzyme
Inhibitor alters shape of enzyme active site
Substrate can no longer occupy enzyme
What is the difference between competitive and non-competitive inhibitors?
Competitive:
Bind to active site
E-S complex form when inhibitor release
Increasing substrate concentration, decreases effect
Non-competitive:
Bind to allosteric binding site
Causes permanent change
Increasing substrate concentration has no effect
How is a peptide bond formed between 2 amino acids to form a dipeptide?
Condensation reaction of 2 amino acids
Between amino group and carboxyl group
2 proteins have the same number and type of amino acid but different tertiary structure.
Why?
Different sequence of amino acids
Causes hydrogen bonds in different places
How do you test for sucrase?
Biuret test
Purple colour = positive
What is the process of producing a calibration curve?
- Make maltose solutions of known concentrations and do Benedict test
- Use colorimeter to measure value of each solution and plot calibration curve
X-axis: concentration
Y-axis: colorimeter reading - Find concentration of sample from calibration curve
What are 4 factors that affect enzyme activity?
- Enzyme concentration
- Substrate concentration
- Temperature
- PH
How is a control set up in a practical measuring enzyme activity?
Replace enzyme solution with distilled water or boiled enzyme solution
How can results of practical measuring enzyme activity be used to find initial rate of reaction?
Plot results on graph of ‘rate of reaction’ against ‘time’
Draw tangent at time
What is the effect of temperature on enzyme activity?
Temperature increases:
- Kinetic energy increases
- E-S complexes form
- Rate of reaction increases up to optimum temperature
What happens after temperature reaches optimum and goes beyond that in enzyme activity?
- Enzyme tertiary structure breaks
- Changes shape of active site
- Substrate and enzyme no longer complementary
- Rate of reaction decreases
What is the practical method to measuring the effect of concentration of enzyme activity, using trypsin and milk?
- Place X on bench
- Measure 5ml of milk and place in flat bottomed tube
- Measure 5ml of 0.25% trypsin
- Add trypsin to test tube and time how long it takes for milk to go clear- when X can be seen.
- Record time
- Repeat for all other concentrations of trypsin
- Repeat each concentration 3 times
What is the risk associated with handling enzymes?
Low risk
Avoid contact with skin
Wear eye protection
How would you make a 1 in 10 dilution using bacteria and sterile liquid and then how would you use that to make a 1 in 1000 dilution of the original liquid culture of bacteria?
Add 1 part bacteria to 9 parts sterile liquid to make 10(-1) dilution.
Repeat using 9 parts fresh liquid and 1 part of 10(-1) and 10(-2) dilutions to make 10(-3) dilution.
What is a control experiment when testing for starch and why is it important?
Disc should be soaked in pure amylase
Show how amylase is responsible for colour change.
How do R groups interact to form the tertiary structure of a protein?
Some R groups repel
Disulphide bridges between cysteine
Ionic bonds between oppositely charged R groups
Hydrogen bonds
What is the Biuret solution?
Sodium hydroxide and copper sulfate
