AQA A level Biology Topic 1

What is a polysaccharide?

What is a polysaccharide?

Two or more monosaccharides are joined together by condensation reactions

What are carbohydrates?

Large, complex molecules that are made from monosaccharides

What elements are in carbohydrates?

Carbon, hydrogen, oxygen

What type of sugar is glucose?
What does this mean?

A hexose sugar.
A monosaccharide with six carbons

Beta (β) glucose molecule

What forms between two molecules when water is released?
What forms when two monosaccharides join together?

A glycosidic bond
A disaccharide

What is the food test for sugars?

Benedict's test

Describe the food test for reducing sugars

Add Benedict's reagent to a sample then heat it in a water bath until it boils.
If reducing sugars are present then a coloured precipitate forms.

Describe the food test for non-reducing sugars

Add dilute hydrochloric acid to the sample and carefully heat in a water bath until it boils. Neutralise by adding sodium hydrogencarbonate. Then add Benedict's reagent and a colour precipitate will form

What two polysaccharides is starch made of?

amylose and andamylopectin

What is amylose?

A long, unbranched chain of alpha glucose.

Describe the food test for starch

To a sample, add iodine dissolved in potassium iodide solution

What are three examples of monosaccharides?

Glucose, fructose and galactose

What are the two types of glucose?

Alpha and beta

What is an isomer?

Molecules with the same molecular formulae but different connections and therefore different properties

Alpha (α) glucose molecule

What is a condensation reaction?

Two molecules join together with the formation of a new chemical bond and a water molecule is released when the bond is formed

What is sucrose?

A disaccharide formed from a condensation reaction between a glucose molecule and a fructose molecule

What is lactose?

A disaccharide formed by condensation of a glucose molecule and a galactose molecule

How can polymers be broken into monomers?

Through hydrolysis reactions

How does hydrolysis reactions break polymers apart?

The chemical bonds between monomer is broken with a water molecule

How can sugars be classified?

Reducing or non-reducing

What is the order of the the colour change in the test for reducing sugars?

Blue, green, yellow, orange, brick red

What colour does a highly concentrated sample of reducing sugar turn?

Brick red

How can samples of reducing sugar be compared?

Filter the precipitates and then weigh the precipitates. Compare the masses

What is a negative result in the non-reducing sugar test?

The solution will remain blue

What do plants store excess glucose as?

Starch. When more glucose is needed then the starch is broken down

Describe the structure of amylose

It has a coiled structure due to the angles of glycosidic bonds. It creates a cylindrical shape due to the coils and it allows large quantities to fit into small spaces

What is amylopectin?

A long branched chain of alpha glucose

Describe the structure of amylopectin

It has side branches so enzymes can breakdown the glycosidic easily

What is a positive result for the starch food test?

The sample will turn from bowny-orange to blue-black

What do animals store excess glucose as?

Glycogen

What is glycogen?

A polysaccharide of alpha-glucose

What polysaccharide is glycogen's structure similar to? How is it different?

Amylopectin
It has many more branches

Why are there many branches on glucagon?

It means that the enzymes can reach the bonds fast so stored glucose can be released very fast.

What type glucose is cellulose made of?

Beta

How are the straight cellulose chains linked?

With weak hydrogen bonds. This forms strong fibres called microfibrils. Cellulose provides structural support for the cells which means its ideal for cell walls.

What is a triglyceride?

A kind of lipid.

What is the structure of a triglyceride?

A glycerol with three fatty acids

What are the 'tails' on fatty acids?

Hydrocarbons which are hydrophobic. This means that lipids are insoluble in water

How are triglycerides formed?

A fatty acid reacts with a sugar molecule and makes an ester bond. A water molecule is released. This happens again to form a triglyceride

What are the two types of fatty acids?

Saturated and unsaturated

How can the two fatty acids be differentiated?

The hydrocarbon tails
Saturated fatty acids don't have any double bonds between carbon acids whereas unsaturated fatty acids have at least one double bond between carbons.

What is a phospholipid?

Lipids found in cell membranes

What is the structure of a phospholipid?

A phosphate group and two fatty acids attached to glycerol

What is important about the phosphate group and fatty acids?

The phosphate group is hyrdophilic and the fatty acids are hydrophobic

What does hydrophilic mean?

Attracts water

What does hydrophobic mean?

It repels water

Why are triglycerides good energy storage molecules?

- Long hydrocarbon tails contain lots of chemical energy so it is released when broken down
-They're insoluble so water potential of the cell is unaffected

What structure does phospholipids make in a cell?

The bilayer of cell membrane

Why is are phospholipids suitable for the structure it makes?

It forms two layers with the heads which are hydrophilic and tails are hydrophobic. The heads face outwards. The centre of the bilayer is hydrophobic so water-soluble substances can't pass through easily

What is does the emulsion test check for?

The presence of fat

Describe the process of the emulsion test

Add ethanol to the substance being tested and shake the test tube for about a minute.
Pour the solution into water

What is a positive result for the emulsion test?

A milky emulsion will be visible

How many amino acids are required to form a dipeptide?

Two

What is a polypeptide?

An organic polymer than is made of more than two amino acids.

What is the general structure of amino acids?

A carboxyl group, an amino group and an R group.

How many different amino acids make up all living things?

20

What is the R group?

The variable group that differentiates the amino acids

What reactions form polypeptides?

Condensation

What is the bond between amino acids in polypeptides called?

Peptide bonds

What are the four structural levels in a protein?

Primary, Secondary, Tertiary and Quarternary

What is the primary structure in a protein?

The sequence of amino acids in the polypeptide chain.

What is the secondary structure in a protein?

Hydrogen bonds between amino acids. This forces the chain to either become an alpha coil or beta pleated sheet

What is the tertiary structure in a protein?

More bonds (hydrogen or ionic) form between parts of the polypeptide chain.
When the two molecules of the amino acid cysteine are close then disulfide bridges form. (a sulfur atom from each amino acid bonds)
This forms a 3D structure.

What is the quarternary structure of a protein?

If there are several different polypeptides then the connections between these polypeptides is the quarternary structure.
Or the quarternary structure is the final 3D structure

What is an enzyme?

A specialised protein that often has roles in metabolism

What is an antibody?

A specialised protein that is involved with immune response.

Describe the basic structure of anitbodies

Two light polypeptide chains and two heavy polypeptide chains

Where are transport proteins located?

Cell membranes

What is the role of transport proteins?

Transports molecules and ions across the cell membrane through a channel created in the proteins due to folds.

What is the structure of structural proteins?

Long, parallel polypeptide chains with cross links

What is in structural proteins?

Keratin and collagen

What test is for proteins?

Biuret Test

What is the first stage of the Biuret test?

Add sodium hydroxide solution to the test solution so it is an alkaline solution

What is the second stage of the Biuret test?

Add copper (II) sulphate solution to the alkaline test solution

What is a positive result for the Biuret test?

Purple

In terms of cells, where can enzymes function?

Both within (intracellular) and outside (extracellular)

What is the active site?

The part of the enzyme that has a particular shape which binds to the substrate molecules

How do enzymes speed up the rate of metabolic reaction?

The activation energy is lowered so reactions occur at lower temperatures.

What is an enzyme-substrate complex?

When a substrate fits into an active site on an enzyme

Why do enzyme-substrate complexes lower activation energy? (when joining molecules)

The substrate is held close to the enzyme and reduces the repulsion so bonding is easier

Why do enzyme-substrate complexes lower activation energy? (when breaking down molecules)

The bonds are strained whilst in the active siteso break quicker.

What, on the graph, is used to compare rates of reaction?

Gradient of the line (this may be a tangent at the same time point)

What type of graph is used to show enzyme-controlled reactions?

Line graphs

What does it mean on an enzyme-controlled reaction graph when the line is flat?

No more products are being produced

What is the Induced Fit model theory for enzymes?

Both the active site and substrate change shape so that the shapes completely match

What controls the shape of the active site?

The tertiary structure

What happens if the tertiary structure of the enzyme is altered?

The substrate won't fit into the active site and so the reaction will notbe catalysed.

What determines the primary structure of an enzyme?

Genes. If the genes mutate then the entire enzyme could be useless.

Why does an increase in temperature lead to enzymes working more frequently?

A higher temperature means that the substrates have a higher kinetic energy so they move faster and increases the chances of the substrate colliding with the enzyme is increased

What does denature mean?

change the shape of the active site by heat, acidity, or other effects that disrupt its molecular conformation.

What is the average optimum temperature for most human enzymes?

37°C

What is the average optimum pH of enzymes in humans?

pH7

What causes the enzyme to become denatured? (pH)

If the the pH is not the optimum then the H+ and OH- will damage the ionic and hydrogen bonds in the tertiary structure.

How does enzyme concentration affect enzyme activity?

A higher enzyme concentration means that there is a higher chance of the substrate colliding with an active site.

At what point does the rate of reaction hinder if the enzyme concentration is high?

When the concentration of substrate is less than the concentration of enzymes.

What does amylase break down?

It catalyses the breakdown of starch to maltose

What apparatus is needed to calculate the speed of breakdown of starch?

A starch solution, test tube, pipette, spotting tile, iodine in potassium iodide, stopwatch

What is the experiment to calculate the speed that substrates are broken down?

Potassium iodide is added to each well of the tile and a drop of iodine is added to each. Amylase and starch (concentrations should be know) are mixed in a test tube. A drop of this mixture is added one well. Check the colour at regular intervals (e.g every 20 seconds)