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Biological molecules

Terms in this set (58)

State the chemical elements that make up these biological molecules: (4)
Carbohydrates - Carbon, hydrogen, oxygen
Lipids - Carbon, hydrogen, oxygen
Proteins - Carbon, hydrogen, oxygen, nitrogen (R groups may contain sulphur)
Nucleic acids - Carbon, hydrogen, oxygen, nitrogen, phosphorous
Describe a biological function of these cations: (5)
Ca²⁺ - Stimulates the vesicles with neurotransmitter to move to the presynaptic membrane
Na⁺ - Involved in transmission of action potentials along a neurone
K⁺ - Involved in transmission of action potentials along a neurone
H⁺ - Used in the active loading of sucrose into the companion cells
NH₄⁺ - Absorbed from the soil by plants - used a source of nitrogen
Describe a biological function of these anions: (5)
NO₃⁻ - Absorbed from the soil by plants - used a source of nitrogen
HCO₃⁻ - How the majority of carbon dioxide is carried in the blood
Cl⁻ - Acts a cofactor for amylase
PO₄³⁻ - Needed for the synthesis of nucleotides
OH⁻ - pH determination - makes solutions alkaline
Describe the difference between a monomer and polymer. Give an example of each. (4)
A monomer is a small, basic molecular unit.
For example an amino acid, monosaccharide or nucleotide.
A polymer is a large, complex molecule made up of lots of monomers bonded together in a long chain.
For example proteins, polysaccharides and nucleic acids.
Describe what happens in a condensation reaction. (4)
Two molecules are bonded together
A covalent bond is formed
Water is formed as a by product
From the OH from one molecules and the H from the other
Describe what happens in a hydrolysis reaction. (4)
A larger molecule is split into two smaller ones
A covalent bond is broken
Water is added
To form the OH of one molecules and the H of the other
Draw the structure of alpha glucose.
Draw the structure of ribose
Describe the main difference between glucose and ribose
Glucose is a hexose sugar with 6 carbon atoms.
Ribose is a pentose sugar with 5 carbon atoms.
Explain how the structure of glucose aids its function
Soluble - therefore easily transported
The chemical bonds contain a lot of energy
Describe how to carry out a qualitative test for reducing sugars
Add Benedict's solution to the sugar solution
Place in a water bath and heat to 80°C
If solution stays blue is a negative result - no reducing sugar
A green, yellow, orange or red precipitate is a positive result
Can be a semi quantitative test
Describe how to carry out a test for a non-reducing sugar
Carry out reducing sugar test first
If negative, obtain a new sample of the sugar solution
Add dilute hydrochloric acid and boil
Neutralise with sodium hydrogencarbonate
Repeat the Benedict's test for a reducing sugar
If blue, no sugar present (reducing or non-reducing)
A green, yellow, orange or red precipitate indicates non-reducing sugar is present
Describe how to carry out a quantitative test for a reducing sugar
Complete serial dilutions to obtain different concentrations of reducing sugar
Measure out the same volume of each reducing sugar solution
Add the same volume of Benedict's solution to each reducing sugar solution
Heat in a water bath at 80°C for 10 minutes
Filter each solution to remove the precipitate
Pour each solution into a cuvette
Turn on the colourimeter and put on the red filter
Zero with a cuvette of distilled water
Measure the transmission of light of each solution
Plot a calibration curve
Test the unknown solution of reducing sugar and use the calibration curve to estimate the concentration of reducing sugar
State the monosaccharides present in these disaccharides: sucrose, lactose, maltose
Sucrose - One alpha glucose molecule, one fructose molecule
Lactose - One beta glucose molecule and one galactose molecule
Maltose - Two alpha glucose molecules
Describe the synthesis of a disaccharide
Condensation reaction
Forms a 1,4 - glycosidic bond
Water is formed
From a hydrogen atom of one sugar and a hydroxyl group (OH) from the other
Describe the synthesis of two monosaccharides from a disaccharide
Hydrolysis reaction
Breaks a 1,4 - glycosidic bond
Water is needed for the reaction
Adds a hydrogen atom to one sugar and a hydroxyl group (OH) to the other
Describe the structure of starch
Polysaccharide of alpha glucose
A mixture of amylose and amylopectin
Amylose is unbranched chain of alpha glucose molecules
All 1,4 - glycosidic bonds
Coiled structure
Amylopectin is branched
Contains 1,4 and 1,6 - glycosidic bonds
Explain how the structure of starch aids its function
Insoluble - doesn't affect the water potential of the cell
The coiled structure of amylose makes it compact
Can store a lot of starch in a small space
The branches of amylopectin allow enzymes to hydrolyse it quickly
Glucose can be released more quickly
Describe the structure of glycogen
Polysaccharide of alpha glucose
Lots of branching
Contains 1,4 and 1,6 - glycosidic bonds
Explain how the structure of glycogen aids its function
Insoluble - doesn't affect the water potential of the cell
Compact - can store a lot in a small space
Lots of branches allow enzymes to hydrolyse it quickly
Glucose can be released more quickly
Describe the structure of cellulose
Polysaccharide of beta glucose
Alternate beta glucose molecules are flipped over
Forms straight cellulose chains
Cellulose chains bonded together with hydrogen bonds
This forms microfibrils
Microfibrils join together to form macrofibrils
Explain how the structure of cellulose aids its function
Many hydrogen bonds provide structural strength
Necessary for the cell wall
Draw the general structure of an amino acid
Describe how a dipeptide is formed from two amino acids
Condensation reaction
The OH of the carboxylic acid group in one amino acid bonds with a H atom from the amino group of the other amino acid
This produces water
Forms a peptide bond
Define the term primary structure
The sequence of amino acids in a polypeptide chain
Describe how the secondary structure of a protein is formed
The polypeptide chains coil to form an alpha helixes
Or fold to forma beta pleated sheet
Describe how the tertiary structure of a protein is formed (include details of the different bonds that hold the protein in its tertiary structure).
The alpha helixes and beta pleated sheets coil and fold further.
Held in place by lots of bonds:
Ionic bonds between amino acids of opposite charge
Hydrogen bonds between amino acids with slight charges
Disulphide bonds that form between sulphur atoms in two cysteine amino acids
Hydrophilic interactions - hydrophilic amino acids are found on the outside of the protein.
Describe two examples of where the tertiary structure of a protein is crucial to its function
1. Enzymes
Shape of active site is specific
And complementary to the substrate
If the tertiary shape is altered, the enzyme can't hydrolyse the substrate
2. Hormones
Shape is specific and complementary
To the receptor
If the tertiary shape is altered the hormone won't combine with the receptor
Define the term quaternary structure
A protein made up of different polypeptide chains
Define the term conjugated protein
A protein with a non-protein group attached.
The non-protein group is called a prosthetic group
Describe the general structure of a globular protein
Spherical
Amino acids with hydrophilic R groups are on the outside
Soluble
Describe the structure of heamoglobin
Four polypeptide chains
Each polypeptide chain has a haem group as a prosthetic group.
Each haem group contains iron.
Describe the function of heamoglobin
To carry oxygen in erythrocytes.
Describe the structure of insulin
Two polypeptide chains
Held together with disulphide bonds
Describe the function of insulin
Hormone
Reduces blood glucose concentration
Describe the structure of amylase
A single chain of amino acids
Describe the function of amylase
Enzyme
Catalyses the hydrolysis of starch
Describe the general features of fibrous proteins
Insoluble
Strong
Structural proteins
Describe the properties of collagen
Very strong
Minerals can bind to increase rigidity
Describe where collagen is found
Found in connective tissue, such as skin, bone and muscle.
Describe the properties of keratin
Can be flexible (if fewer disulphide bonds)
Or can be hard and tough (if more disulphide bonds)
Describe where keratin is found
Found in nails, skin hair, feathers and horns
Describe the properties of elastin
Allows tissues to return to their original shape after thy have been stretched
Describe where elastin is found
Found in elastic connective tissue, such as in large blood vessels and ligaments.
Describe how to carry out a biochemical test for proteins
Add a few drops of biuret solution
Blue = no protein, negative result
Purple = protein, positive result
Describe the difference between the mobile phase and the stationary phase in chromatography
Mobile phase - the molecules can move. This is usually the liquid solvent
Stationary phase - the molecules can't move.
This can be chromatography paper or a silica gel in thin layer chromatography
Describe how the molecules are separated in chromatography
The mobile phase (solvent) moves through the stationary phase (paper).
The longer the molecule is in the mobile phase, the further it will travel up the paper.
Describe how to separate a mixture of amino acids by paper chromatography
Draw a pencil line across a piece of chromatography paper.
Put a concentrated spot of the amino acid solution on the line.
Add a small volume of solvent to a beaker.
Stand the chromatography paper in the beaker, making sure that the pencil line is above the solvent.
Cover with a lid to stop the solvent evaporating.
When the solvent nearly reaches the top of the chromatography paper remove the paper from the beaker.
Mark the solvent front with a pencil line.
Leave the paper to dry out.
Spray the chromatogram with ninhydrin solution to turn the amino acids purple.
This should be done in a fume cupboard.
Once dry, mark the centre of each amino acid spot, with a pencil.
State the formula used to calculate an Rf value
Rf = distance travelled by spot / distance travelled by solvent
Describe the structure of a triglyceride (include details of saturated and unsaturated fatty acids
One glycerol molecule
Three fatty acids tails
The fatty acids can be saturated or unsaturated
Saturated fatty acids only contain single bonds between the carbon atoms
Unsaturated fatty acids have at least one double bond between the carbon atoms
Describe how triglycerides are formed
A condensation reaction occurs
Between the glycerol molecule and the fatty acids
A hydrogen atom is removed from the glycerol
An OH group is removed from the fatty acids
To form three molecules of water
An ester bond is formed
Describe the structure of a phospholipid
One glycerol molecule
One phosphate group
Two fatty acid tails
The phosphate group is hydrophilic and the fatty acids are hydrophobic
Describe the functions of triglycerides and explain how their structure aids the function
Energy storage molecules
They are insoluble
And therefore don't affect the water potential of the cell
The fatty acid tails contain a lot of chemical energy
This energy is released when the bonds are broken
Describe the functions of triglycerides and explain how their structure aids the function
Form the bilayer in membranes
The phosphate heads are hydrophilic and the fatty acid tails are hydrophobic
Therefore the phosphate heads face outwards and the tails face inwards
The fatty acid tails act as a barrier to water soluble substances
Describe the functions of cholesterol and explain how its structure aids the function
Strengthen the cell membrane
Small, flat shape
Therefore, it can fit in between the tails of the fatty acids in the membrane
The cholesterol can bind to the tails of the phospholipids
Therefore making the membrane les fluid and more rigid
Describe the biological test for lipids
Shake the sample with ethanol
Pour the solution into water
If lipid id present the solution turns white
If no lipid is present the solution stays clear
Draw a diagram of 3 water molecules. Include the partial charges, a covalent bond and a hydrogen bond
Describe three properties of water. For each one, explain how it aids living organisms
Ice is less dense than water
Ice will float and insulate the water underneath
The whole body of water does not freeze

Water has a high specific heat capacity
Because the hydrogen bonds can absorb a lot of energy
Therefore it is thermally stable
Good habitat, particularly for ecotherms

Water has a high latent heat of evaporation
Because it takes a lot of energy to break the hydrogen bonds
Therefore, can be used to cool organisms via sweating

Water has high cohesion
Because it is a polar molecule
Therefore it flows by mass flow through the xylem and phloem

Water is a good solvent
Because it is a polar molecule
Therefore ions and glucose easily dissolve and can be transported
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