ALL of Biological molecules 1.1 AQA

Aqa Alevel Biology new spec

condensation definition

forming a chemical bond removing one water molecule

hydrolysis definition

breaking a chemical bond using one molecule of water

Define monomer

A small repeating unit which can form a polymer

Explain how proteins or antibodies are digested

Peptide bonds are hydrolysed

Endopeptidases break internal peptide bonds

Exopeptidases break terminal bonds

Membrane bound dipeptidases break di-peptidases to amino acids

what elements do carbohydrates contain?

C,H,O

give 4 examples of monosaccharides

alpha glucose

Beta glucose

fructose

galactose

give 3 examples of disaccharides

sucrose

maltose

lactose

give 3 examples of polysaccharides

cellulose (plants)

starch (plants)

glycogen (animals)

What is the plant cell wall made of?

cellulose

sucrose is made of ___ and ___

glucose+fructose

lactose is made of ___ and ___

glucose+galactose

maltose is made of ___ and ___

glucose+glucose

Disaccharide definition

carbohydrates formed when 2 monosaccharides are joined by a glycosidic bond by a condensation reaction.

monosaccharide defintion

is the individual monomer of carbohydrates

give the properties of monosaccharides, disaccharides and polysaccharides

monosaccharides- soluble, energy source for respiration

disaccharides-soluble, energy transport and storage

polysaccharides-insoluble, energy storage

definition of a glycosidic bond

the bond between two monosaccharides

define polysaccharide

a carbohydrate formed from many repeating monoscharides joined by glycosidic bonds via condensations reactions

what is cellulose? and what is its structure? how does it relate to it’s function?

• a polysaccharide made of many 'β' (beta) glucose monomers

• long, straight, unbranched chains of beta glucose held in parallel by hydrogen bonds

• forming microfibrils

• the many hydrogens provide structural support to cellulose for plant cell walls

• contains 1,4 glycosidic bonds

what is glycogen ? and what is its structure? how does it relate to it’s function? where is it located in?

• a polysaccharide made of many ‘α’ (alpha) glucose

• highly branched structure- providing a large surface are for rapid hydrolysis into glucose for respiration by enzymes

• insoluble-doesn’t affect the water potential of the cell

• large molecule-doesn’t pass through the cell membrane

• animals - mainly muscle and liver cells

• contain 1,4 and 1,6 glycosidic bonds

what is starch? and what is its structure? how does it relate to it’s function? where is it located in?

a polysaccharide made up of many ‘α’ (alpha) glucose monomers

made of 2 polymers

amylose- unbranched helical structure- making it compact and can lot’s can be stored in a small space

amylopectin- branched molecule- providing a large surface area for the rapid hydrolysis into glucose for respiration by enzymes.

insoluble- won’t affect the water potential of the cells

large molecule-so it won’t pass through the cell membrane

found only in plants

please draw the structure of an ‘α’ (alpha) glucose monomer

please draw the structure of a 'β' (beta) glucose monomer

draw the formation of maltose and the structure of maltose. (2 marks)

explain how maltose is formed and broken down (3 marks)

maltose is formed when two alpha glucose monosaccharides are joined by a glycosidic bond, via a condensation reaction. Releasing one molecule of water.

maltose is broken down by maltases.

where maltase catalyses the hydrolysis of maltose into two alpha glucose monosaccharides with the addition of one molecule of water to break the glycosidic bond.

explain how sucrose is formed and broken down (3 marks)

sucrose is formed when one fructose and one a glucose monosaccharide are joined by a glycosidic bond, via a condensation reaction. Releasing one molecule of water.

Sucrose is broken down by sucrases.

Where sucrase catalyses the hydrolysis of sucrose into one fructose and one glucose monosaccharide with the addition of one water molecule to break the glycosidic bond.

explain how lactose is formed and broken down (3 marks)

lactose is formed when one galactose and one glucose monosaccharide are joined by a glycosidic bond, via a condensation reaction. Releasing one molecule of water.

Lactose is broken down by lactases.

Where Lactase catalyses the hydrolysis of lactose into one galactose and one glucose monosaccharide with the addition of one water molecule to break the glycosidic bond.

What is the chemical equation for both alpha and beta glucose?

C6 H12 O6

Compare the structures of Cellulose and Chitin

Both are polysaccharides made up of many beta-glucose monomers

Both are joined by glycosidic bonds

Both have a linear shape and form long straight unbranched chains.

What is the term used to describe the different structures of alpha and beta glucose

Isomerism

Suggest why the water potential in fruits containing starch decreases as the fruits are stored (3 marks)

Because the starch is being hydrolyed by amylase into maltose.

Maltose is a disaccharide that is soluble in water

Therefore lowers the water potential

Describe the transport of carbohydrates in plants (5 marks)

Sucrose is actively transported into the phloem by companion cells

Lowering the water potential in the phloem, allowing water to enter from the xylem by osmosis

This increases the hydrostatic pressure in the phloem, creating a pressure gradient

Creating mass flow to respiring cells

Sucrose is then unloaded from the phloem to the cells by active transport

Compare and contrast the structure of starch and the structure of cellulose

Starch has a helical structure while cellulose has a linear structure

Starch is a polysaccharide made up of many alpha glucose monomers, while cellulose is a polysaccharide made up of many beta glucose monomers

Starch is highly branched while cellulose is not

Starch and cellulose both have C,H,O

Both have glycosidic bonds

Starch has amylose and amylose pectin while Cellulose does not

Describe how starch is digested (4 marks)

The glycosidic bonds in starch is hydrolysed by amylase, converting starch into maltose.

The glycosidic bonds in maltose are then hydrolysed by membrane bound maltase, converting maltose into alpha glucose

Explain the importance the structure of starch

helix is compact and can fit in small spaces

branches increase surface area for rapid hydrolysis back into glucose.

efficient for storing and source of glucose

Insoluble- wont change (Ψ) water potential

Explain the importance the structure of cellulose

very strong (lots of hydrogen bonds)

cell wall provides structural support to the plant cell

Insoluble- wont change (Ψ) water potential

Explain the importance the structure of glycogen

large surface area for rapid hydrolysis into glucose

Insoluble- wont change (Ψ) water potential

What is the test for starch?

1. add iodine solution

2. positive result- solution turns from orange to blue black

What is the test for reducing sugars?

1. add Benedicts solution and heat in water bath for 5 minutes at 80 C

2. positive result: solution turns from blue to a red precipitate

What is the test for non-reducing sugars? (done after the test for reducing sugars)

1. add acid and boil

2. let it cool

3. add an alkaline to neutralize

4. then add Benedicts reagent and heat

5. positive result: turns blue to red precipitate

The benedicts test is describes as a semi-quantitative test. explain what is mean by this. (1 mark)

the benedicts test is an approximate indication of concentration.

doesn’t provides numerical values

describe how you would test for a sample containing an unknown concentration of glucose. without a colorimeter (5 marks)

prepare a dilution series of 5 known concentrations of glucose in 5 test tubes.

label them. and label a test tube containing the sample

add benedicts reagent to all of them and heat in a water bath for 5 minutes at 80 C

colour change will be from blue green to yellow to orange to brick red (depending on concentration)

then compare the colour of the samples to the known concentrations.

describe how you would test for an unknown concentration of glucose. using a colorimeter (6 marks)

use a dilution series of 5 known concentrations of glucose

carry out the benedicts test for each of them and the unknown sample

place the samples in cuvettes and place them in the colorimeter

record the absorbance of light

plot a graph of absorbance against concentration of glucose

find the absorbance of light of the unknown value, use the graph to find the concentration.

give an example of a non-reducing sugar

sucrose

defintion of a reducing sugar

a sugar that is able to donate electrons to another chemical

Give 2 examples of lipids

Triglycerides and phospholipids

Explain how triglycerides are formed

Triglycerides are formed by 3 condensation reactions between the glycerol and 3 fatty acid chains. Forming 3 ester bonds between them. Releasing three water molecules.

Explain how phospholipids are formed

Where 2 condensation reaction occur between the glycerol that’s attached to a phosphate group and two fatty acid chains. Forming 2 ester bonds and releasing 2 Water molecules

What is the difference between saturated and unsaturated fatty acid chains?

What similarity do they have?

Saturated

• the hydrocarbon has only single C-C bonds, no C=C bonds

Unsaturated

• the hydrocarbon has at least one C=C bond.

Both have a hydrocarbon

Give 4 Properties of triglycerides and their importance

Due to the large ratio of C-H bonds compared to the number of Carbon atoms a lot of energy can be stored. Making them a good for energy storage

Due to high ratio of hydrogen atoms they can be oxidised to release water. Making them a good source of water for animals in the desert. E.g Camels

Large and hydrophobic. Making them insoluble to water, doesn’t affect water potential.

Low/small mass. Therefore a lot can be stored without increasing mass.

Explain why phospholipids can form a bilateral but triglycerides cannot

Triglycerides are fully hydrophobic and non polar

While phospholipids are both hydrophobic and hydrophilic, as it’s consists of a hydrophilic phosphate head that attracts water and hydrophobic fatty acid tails.

Give the properties of phospholipids and how it’s important

They have a polar,hydrophilic head face outwards

And non-polar hydrophobic fatty acid tails facing inwards

This is importantly in the formation of the phospholipid bi-layer of the cell membrane. Where only small, non-polar lipid soluble molecules can diffuse across it.

What is the test for lipids?

• Add ethanol and mix

• Then add distilled water and shake

• Positive result- a white emulsion forms

why do lipids form an emulsion in the test for lipids? (2 marks)

lipids are insoluble to water, but soluble in ethanol

when mixed in water. lipid droplets disperse, forming a white emulsion

What are amino acids?

Monomers from which proteins are made

Draw the structure of an amino acid

Explain how dipepetides and polypeptides are formed

A condensation reaction happens between 2 amino acids

Many condensation reactions of amino acids

What is the primary structure of a protein (1 mark)

The sequence of amino acids, held by peptide bonds

What is the secondary structure of proteins (2 marks)

The sequence of amino acids causes the protein molecule to bend into an alpha helix shape or beta pleated sheet.

Held by hydrogen bonds.

What is the tertiary structure of a protein? (3 marks)

Further folding of the secondary structure

To form a 3D structure

Held in place by ionic, hydrogen and disulfide bonds.

What is the quaternary structure of proteins? And give an example

A protein made of more than one polypeptide chain.

Haemaglobin- has 4 polypeptide chains

Describe how a quarternary protein is formed from its monomers (5 marks)

Primary structure is formed by amino acids joined by peptide bonds to form a peptide a chain

Secondary structure is formed by hydrogen bonding as is either an alpha helix or beta pleated sheet

Tertiary structure is formed by ionic, hydrogen and disulfide bonds between R groups

Quarternary structure contains more than one polypeptide and is formed by further ionic, hydrogen and disulfide bonding between polypeptides

What would happen to an enzyme if the sequence of it’s the amino acids changes?

1. If even one amino acid in the sequence is different

2. then it will cause the ionic, hydrogen or sulphide bonds to form in different locations.

3. Which will change the 3D shape

4. Causing the enzyme’s active site to have a different shape

5. Or a carrier proteins

6. Or a carrier protein’s binding site changes

What is the test for proteins?

1. Add biuret reagent

2. A positive result: solution turns blue to purple

Definition of an enzyme (1 mark)

Are tertiary structure proteins

which are biological catalysts which catalyse reactions by lowering the activation energy.

Describe the lock and key model of enzymes

The active sit is substrate specific and will only for an enzyme substrate complex with the specific substrate that are complementary in shape.

The active site is a fixed shape

Describe the induced fit model of enzymes

(Currently Accepted model)

Substrate enters to the active site

The enzymes active site distorts around the substrate becoming complementary and forming an enzyme substrate complex.

The enzyme Puts strain on the bonds which lowers the activation energy

causing to be broken into products

Enzyme returns to original shape

What are the 5 factors that affect Enzymes? (3 marks)

1. Temperature

2. pH

3. Substrate conc.

4. Enzyme conc.

5. Presence of Inhibitors

Explain how temperature can affect enzymes (2 marks)

If temperature is too low- there is not enough KE for successful collisions between the substrate and enzyme.

If temperature is too high- enzymes will denature and the active site changes shape and will no longer be complementary.

fewer enzyme substrate complexes formed

Explain how pH can affect enzymes (2 marks)

When pH levels are too high or too low it will interfere with the charges in the amino acids in the active site. Causing its tertiary structure to change shape. And the active site is no longer complementary.

The enzyme denatures and fewer enzyme substrate complexes are formed.

Explain how substrate conc./ enzyme conc. can affect enzymes (2 marks)

Low conc. of substrate -Fewer successful collisions between the substrates and enzymes.fewer enzyme substrate complexes.

Low conc. of enzymes- fewer active sites available and becomes a limiting factor.

What is a competitive inhibitor and how does it reduce the rate of reactions?

Competitive inhibitors are similar in shape with the substrate and can bind to the active site.

Preventing substrates from being able to bind.

Reducing the rate of reaction.

How can you stop competitive inhibitors from competing with the substrates?

Increase conc. of substrate, so that it out-competes the inhibitors.

What are non-competitive inhibitors and why are they so bad?

Non-competitive inhibitors bind to an enzymes binding site and causes the active site to permanently change shape.

Causing the substrate to no longer be complimentary with the enzyme’s active site. And no longer for enzyme substrate complexes.

Increasing the conc. of substrate does nothing.

Label the lines on this graph

Give 2 examples of polymers of nucleic acids

1. Deoxyribonucleic acid (DNA)

2. Ribonucleic acid (RNA)

Draw and label the structure of a nucleotide ( both DNA and RNA)

What are the differences and similarities of DNA and RNA?

DNA has thymine bases, while RNA has uracil bases instead

DNA has deoxyribose Pentose sugar, while RNA has just ribose Pentose sugar

DNA is double stranded, while RNA is single stranded

DNA has a double helical shape, while RNA is linear

Explain what a polynucleotide is and how it’s formed

It is a polymer of nucleotides.

And is created via condensation reaction between the deoxyribose sugar and the phosphate group.

Forming phosphodiester bonds.

What are phosphodiester bonds and why are they important in creating polynucleotides?

Phosphodiester bonds are strong covalent bond.

Therefore help ensure the genetic code is not broken down.

Describe the structure of DNA (2 marks)

Two polynucleotide chains that form a double helix.

The 2 chains are held by hydrogen bonds between specific complementary nitrogenous bases.

What are the complimentary base pairs in DNA and RNA? And how many hydrogen bonds will form between them?

Cytosine and guanine will form 3 hydrogen bonds

Adenine and Thymine/Uracil will form 2 hydrogen bonds

How does the structure of DNA relate to its function or inportance? (5 marks)

Strong phosphodiester bonds,Strong sugar phosphate backbone

Double stranded, forms 2 template strands in semi conservative DNA replication

Weak hydrogen bonds between nitrogen bases, easy broken to form the 2 strands

Very large molecule,carry lots of genetic information

Complementary base pairing allows identical copied of DNA to be made

When does Semi-conservative DNA replication occurs in the cell cycle?

Before mitosis in the S phase

What does ‘semi’ mean in semi-conservative DNA replication

One strand is the original parent strand, and the other strand is newly synthesised

In the new daughter DNA

What are the 2 enzymes in semi-conservative DNA replication? And state their roles. (2 marks)

DNA helicase- hydrolyses the hydrogen bonds between the complementary bases

DNA polymerase- joins adjacent nucleotides, forming a phosphodiester bond via condensation

Describe the process of semi-conservative replication

1. DNA helicase hydrolyses the hydrogen bonds between the complementary bases, causes the polynucleotide strands to unwind.

2. Free DNA Nucleotides are attracted to the exposed bases on the template strands.

3. DNA polymerase joins adjacent nucleotides, forming phosphodiester bonds via condensation reactions.

Draw and label the structure of ATP

Describe how ATP is broken down to release energy and resynthisized

ATP is hydrolysed by ATP hydrolase into ADP and an inorganic phosphate

Releasing energy

ATP is resynthesized by condensation reaction between ADP and an inorganic phosphate

What is the reversible reaction of ATP

ATP + Water ← → ADP + Pi +(energy)

Describe the structure of water

Water is a polar molecule and has uneven charge distribution

Where hydrogen is partially positive and oxygen is partially negative

What are the 5 properties of water and how does it link to their importance? (6 marks)

Water can form hydrogen bonds between other water molecules

Strong cohesion between water molecules, Water can move as one mass (important in the xylem and transpiration). And provides surface tension when water meets the air.

Water is a metabolite and is used in condensation and hydrolysis reactions

A universal solvent as positive and negative ions can be dissolved

Has a high heat capacity, lots of energy is needed to raise the temperature of water by 1 degree Celsius (Buffered temperature changes and helps maintain body temperature)

Large latent heat of vaporisation (lots of energy is needed to vaporise water into a gas, so it provides a cooling effect as it evaporates)

What are 2 physical properties of water?

It’s transparent (let light shine through, important for aquatic plants to photosynthesis. E.g algae)

It’s denser than ice (so when a lake freezes only the top is frozen as ice is less dense than water, providing insulation for aquatic organisms below)

Where are 2 places inorganic ions can be found in?

The cytoplasm and bodily fluids

Give 4 example of ions and explain their importance (4 marks)

Hydrogen ions H+ affect pH

Iron irons Fe 2+. Found in haemoglobin, involved in oxygen transport

Sodium ions Na+. Used in the co-transport of glucose and amino acids

Phosphate ions PO4 3- Found in DNA and ATP, needed in the resynthesis of ATP