Module 1 - Biological Molecules Flashcards
Properties of water?
- ice is less dense than water because it has an open lattice. This means ice is formed on the surface and the water beneath becomes insulated.
- cohesion: because water molecules are polar, they stick to each other creating surface tension at the water’s surface
Draw a basic amino acid
NH2CHRCOOH
Draw the synthesis and hydrolysis of dipeptides and polypeptides
- refer to notes for diagram
- condensation: peptide bond formed, water released
- hydrolysis: peptide bond broken, water added
What is the primary structure?
Sequence of amino acids in a polypeptide chain which make a protein
What is the secondary structure?
Formed when the chain of amino acids coil to form an alpha helix or beta pleated sheet. Hydrogen bonds hold the coils in place.
What 3 bonds stabilise the tertiary structure?
1) disulphide bonds
2) ionic bonds
3) hydrogen bonds
Describe the structure of haemoglobin
Globular protein, consists of 2 alpha chains and 2 beta chains, has a prosthetic group (haem group Fe2+), soluble
Describe the structure of collagen
Fibrous protein, 3 polypeptide chains twisted Into a rope, really strong because of cross links formed by covalent bonds between collagen molecules, insoluble
Example of a globular protein
Haemoglobin
Example of a fibrous protein
Collagen
Draw apha glucose chain form and ring form
Refer to notes
What is the structural difference between a-glucose and b-glucose?
In a-glucose, the OH group on the 1st carbon is below the plane. In b-glucose, the OH group on the 1st carbon is above the plane.
Draw and describe the synthesis and hydrolysis of disaccharides and polysaccharides
Refer to notes for diagram.
Condensation: glycosidic bond formed, water released
Hydrolysis: glycosidic bond broken, water added
What is an example of a disaccharide and a polysaccharide?
Disaccharide = maltose, polysaccharide = amylose
2 examples of a glucose molecules?
Starch and glycogen
An example of a b glucose molecule
Cellulose
What is the use and structure of starch?
- energy storage in plants
- a glucose
- insoluble so does not effect water potential in cell
- straight chain
What is the use and structure of glycogen?
- energy storage in animals
- a glucose
- shorter chains so can be broken into glucose more quickly
- more branches so can form granules in animals and so enzymes can attach to them
- insoluble so doesn’t effect water potential
Describe the use and structure of cellulose
- forms cell wall in plant cells
- b glucose
- straight chains
- b glucosidic bond is only broken down by a specific enzyme humans don’t have
Describe the structure of a cell wall
- made out of cellulose
- arrangement of micro tubules allow the movement of H20
- prevents plant cell from bursting
- polypeptide chains form H2 bonds –> very strong
Describe the structure of a triglyceride?
1 glycerol molecule and 3 fatty acids
Describe the structure of a phospholipid molecule?
1 glycerol molecule, 2 fatty acids and 1 phosphate group
Why are unsaturated fatty acids often oils?
The C=C double bond changes the shape of the hydrocarbon chain, making them more fluid.
How to test for proteins?
Biuret reagent. Blue to lilac.
How to test for reducing sugars?
Heat with Benedict’s solution to 80 degrees in water bath. Blue to red.
What is an example of a reducing sugar?
Glucose
How to test for starch?
Iodine solution, yellow to blue-black
Describe the test for lipids
emulsion tests. Add ethanol and pour into water. Mixture turns cloudy/white
Draw the structure of a nucleotide.
On the left hand side, a circle (this is the phosphate group) joined to a pentagon (this is the sugar molecule. If it’s a DNA nucleotide the sugar molecule is deoxyribose and if it’s a RNA nucleotide the sugar molecule is ribose.) the pentagon is joined to an organic base (eg thymine)
How to find the conc of a reducing sugar (eg glucose) using a colorimeter?
- heat the glucose with Benedict’s until there is no further colour change
- red precipitate formed: the more precipitate formed, the greater the reducing sugar conc
- precipitate filtered out
- place the solution between a colorimeter and a photoelectric cell
- the colorimeter shines a beam of light and the cell picks up percentage transmission
- this can be read off a calibration curve with a set of known concs
What are the complimentary base pairings in DNA?
Adenine (A) - Thymine (T)
Cytosine (C) - Guanine (G)
What is the sugar in DNA called?
Deoxyribose. It has 5 carbons but it is more stable than RNA because it lacks an OH group.
Structure of DNA
2 anti parallel chains twisted together to form a double helix shape. The double helix shape gives the molecule stability. The 2 anti parallel chains are held together by hydrogen bonds.
What does RNA and DNA stand for?
RNA - ribonucleic acids
DNA -deoxyribonucleic acids
What are the three forms of RNA?
Messenger RNA (mRNA)- copies part of DNA because DNA is unable to leave nucleus Ribosomal RNA (rRNA) - found in ribosomes Transfer RNA (tRNA) - carries amino acids to ribosomes
What is a gene?
Sequence of DNA nucleotides that code for a polypeptide
Describe protein synthesis.
1) bases on DNA code for a particular protein
2) this sequence of bases is revealed by splitting open the hydrogen bonds that hold the double helix in place
3) mRNA is formed (copy of coding strand), leaves the nuclear envelope through nuclear pore and attaches to ribosome
4) tRNA brings amino acids to ribosome according to the base sequence on the mRNA
5) amino acids joined by peptide bonds to make the primary structure
What are enzymes?
Speed up metabolic reactions without being used in the process. proteins with a specific tertiary structure that catalyse metabolic reactions.
What are intracellular and extracellular enzymes? Give examples of these.
Intracellular: inside cell. found in the cytoplasm of cells/attached to membranes.
Extracellular: outside cell. Used in the digestive system.
What do enzymes do to the activation energy needed for a reaction?
Enzymes reduce the activation energy needed for a reaction to take place. This means that the reaction can proceed at temperatures much lower than boiling point.
Describe the two enzyme theories.
1) lock and key: the shape of the enzyme’s active site is complimentary to the shape of the substrate. The substrate ‘key’ fits into the active site ‘lock’ and an enzyme substrate complex is formed.
2) induced fit hypothesis: when the substrate collides with the enzyme, the enzyme’s active site changes shape slightly to fit more closely around the substrate.
How does temperature effect enzyme activity?
When heated, the kinetic energy of the molecules increase and they move more quickly. There are an increased number of collisions so the rare of reaction increases.
However, heat also makes the enzymes vibrate. Vibrations can break hydrogen bonds responsible for holding the tertiary structure of the active site.
What are the effects of pH on enzyme activity?
Reducing/increasing pH away from optimum reducing the rate of reaction because the concentration of H+ ions effects the tertiary structure of the enzyme’s active site.
What is the effect of increasing substrate/enzyme conc on the enzyme’s activity?
Increased conc leads to an increased reaction rate because there are either more substrates/more active sites. Eventually a plateau occurs because there are no more substrate molecules.
How do competitive inhibitors work?
Competitive inhibitors: similar shape to substrate. The competitive inhibitor fits into active site so substrate can’t.
How do non competitive inhibitors work?
Non competitive inhibitors bind to a region away from the active site. This disrupts the tertiary structure of the active site and enzyme substrate complexes can no longer form.
What are co enzymes?
Coenzymes are small, organic non protein molecules that bind to the active site temporarily at the same time or just after the substrate.
They are recycled for use again (unlike substrates).
What do metabolic poisons do?
Inhibit enzymes
Give one example of a metabolic poison and how it works
Potassium cyanide inhibits cell respiration. It is a non competitive inhibitor. ATP cannot be made so the organism can only respire anaerobicly, causing a build up of lactic acid in the blood.
Outline the process of DNA replication
- Semi conservatively - 1 conserved strand and 1 newly built strand.
- Double helix uncoils, hydrogen bonds break and the free nucleotides align with the complementary base pairings.
- The hydrogen bonds reform.
How are the base pairings of RNA different to the base pairings of DNA?
RNA never contains thymine. Instead, Uracil (U) pairs with Adenine (A)
