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3.1.1 Monomers and polymers
3.1.2 Carbohydrates

What are Polymers? (1 point)

Large, complex molecules composed of long chains of monomers joined together


What monomers are carbohydrates made from? (1 point)

Monosaccharides e.g. glucose, fructose and galactose


What elements do carbohydrates contain? (3 elements)

Carbon, Hydrogen and Oxygen


What is the structure of an alpha-glucose molecule?

H 5 C ------ O H
\ / H \ /
4 C 1 C
/ \ OH H / \
HO 3 C -------- 2 C OH


What is the structure of a beta-glucose molecule?

H 5 C ------ O OH
\ / H \ /
4 C 1 C
/ \ OH H / \
HO 3 C -------- 2 C H


How are monosaccharides joined together? (1 point)

Condensation reactions


What is a condensation reaction? (1 point)

When two molecules join together with the formation of a new chemical bond and a water molecule is released


Which bond forms between two monosaccharides? (1 point)

1,4 glycosidic bond


What do two alpha-glucose molecules joined together form?


H 5 C ------ O H
\ / H \ /
4 C 1 C
/ \ OH H / \
HO 3 C -------- 2 C OH


H 5 C ------ O H
\ / H \ /
4 C 1 C
/ \ OH H / \
HO 3 C -------- 2 C OH

---------------------------- \
H2O /

/ \

\ /


What is a disaccharide? (1 point)

It is formed when two monosaccharides join together


What is maltose formed from? (2 things)

Glucose + glucose


What is sucrose formed from? (2 things)

Glucose + fructose


What is lactose formed from? (2 things)

Glucose + galactose


What is a hydrolysis reaction? (1 point)

Breaks the chemical bond between monomers using a water molecule


Describe the Benedict's test for reducing sugars (3 points)

Add benedict's reagent to a sample
Heat in a water bath
If test is positive a coloured precipitate will form. the solution will change from blue to brick-red depending on concentration.


Describe the Benedict's test for non-reducing sugars (5 points)

If test for reducing sugars is negative, you need to break down sample into monosaccharides by adding dilute hydrochloric acid and heat in water bath.
Then neutralise it with sodium hydrogencarbonate.
Carry out normal test for reducing sugars
If test is positive and it turns brick-red, a non-reducing sugar was present
If test is negative the solution will stay blue meaning sample didn't contain any sugar


What is a polysaccharide? (1 point)

Formed when more than two monosaccharides are joined together by condensation reactions with glycosidic bonds


Polysaccharide - Starch
What monomers is it made from? (1 point)

Made up of chains of alpha-glucose monosaccharides linked by 1,4 glycosidic bonds formed by condensation reactions


Polysaccharide - Starch
Describe its structure (2 points)

Chains are unbranched and helical coiled structure like a cylinder (Amylose) or
Chains are branched (Amylopectin)


Polysaccharide - Starch
Where is it found? (3 points)

Found in many parts of a plant in form of small grains. Especially in seeds and storage organs e.g. potatoes
Never found in animal cells


Polysaccharide - Starch
What is its function? (1 point)

Main role is energy storage and it can be broken down to provide energy


Polysaccharide - Starch
How does its structure relate to its function? (5 points)

It is insoluble so doesn't affect water potential as water not drawn in by osmosis
Being large and insoluble means it does not diffuse out of cells
Being unbranched means it is compact and therefore can be stored in small spaces
Being branched means it has many ends so can be acted on by enzymes simultaneously meaning glucose monomers are released rapidly
Easily hydrolysed to form alpha glucose which is easily transported and used in respiration


Describe the iodine test for starch (2 points)

Add iodine dissolved in potassium iodide solution to a test sample
If starch is present, sample changes from
browny-orange to a dark, blue-black colour


Polysaccharide - Glycogen
What monomers is it made from? (1 point)

Made up of chains of alpha glucose


Polysaccharide - Glycogen
Describe its structure (1 point)

Has shorter chains to starch and is more highly branched so is readily hydrolysed


Polysaccharide - Glycogen
Where is it found? (2 points)

Animals and Bacteria
Never in Plants


Polysaccharide - Glycogen
What is its function? (3 points)

Major carbohydrate storage of excess glucose in animals
Stored as small granules mainly in muscles and liver
Small mass of carbohydrate stored as fat is main storage molecule in animals


Polysaccharide - Glycogen
How does its structure relate to its function? (5 points)

It is insoluble so does not draw water into cells by osmosis
It is insoluble so does not diffuse out of cells
It is compact so can be stored in small space
It is more highly branched so has more ends that can be acted on by enzymes so can be more rapidly broken down to form glucose monomers used in respiration. This is important to animals with higher metabolic rate and higher respiratory rate than plants as they are more active


Polysaccharide - Cellulose
What monomers is it made from? (1 point)

Made of monomers of beta-glucose held by 1,4 glycosidic bonds


Polysaccharide - Cellulose
Describe its structure (4 points)

Cellulose has straight unbranched chains which run parallel to each other, allowing hydrogen bonds to form cross-linkages between adjacent cells.
The hydrogen bonds are weak but lots together are strong
Cellulose molecules are grouped together to form microfibrils which are arranged in parallel groups called fibres
Every second beta glucose is inverted (rotated 180') to form straight linear chain structure instead of helical structure


Polysaccharide - Cellulose
Where is it found? (1 point)

In plant cell walls


Polysaccharide - Cellulose
What is its function? (5 points)

It is a structural polysaccharide in plants
Due to its strength it is a valuable structural material
Provides rigidity to plant cell and prevents cell from bursting (cell lysis) as water enters by osmosis
It does this by exerting an inward pressure that stops any further influx of water. Therefore living plant cells are turgid and push against one another, making parts of plant rigid
It is important for maintain stems and leaves in turgid state so they can provide maximum surface area for photosynthesis


Polysaccharide - Cellulose
How does its structure relate to its function? (2 points)

The cellulose molecular chains run parallel to each other and are cross linked by hydrogen bonds to add collective strength
These molecules are grouped to form microfibrils which are grouped to form fibres which all provide more strength


3.1.3 Lipids

What are the types of lipids? (4 points)

Triglycerides (fats and oils)


What are the functions of lipids? (8 points)

Substrate for respiration
Storage of energy
Protection of organs
Buoyancy and streamlining in aquatic mammals
Cell membranes
Water proofing


What is the solubility of lipids? (2 points)

Lipids are insoluble in water
Lipids are soluble in organic solvents (alcohol and acetone)


What is the difference between fats and oils? (2 points)

Fats are solids at room temperature whereas oils are liquids
Fats are saturated whereas oils are unsaturated


Diagram of structure of a fatty acid

O (Carbon atom links fatty acid to glycerol)
C---R (Variable R group hydrocarbon tail)


What is a saturated fatty acid? (1 point)

Saturated fatty acids don't have any double bonds between their carbon atoms


What is an unsaturated fatty acid? (2 points)

Unsaturated fatty acids have at least one double bond between carbon atoms which causes chain to bend the molecule so they cannot pack as tightly together.
This makes them a liqid at room temperate


How are triglycerides formed? (3 points)

The glycerol molecule joins to a fatty acid by a condensation reaction
3 ester bonds are formed (when a carboxylic group -COOH reacts with hydroxyl group -OH) and molecule of water released
All have a carboxyl group and a hydrocarbon chain attached


What is the structure of triglycerides? (4 points)

One molecule of glycerol with three fatty acids attached to it
Fatty acid molecules have long tails made of hydrocarbons.
The tails are hydrophobic (repel water molecules). These tails make lipids insoluble in water


How does the structure of triglycerides relate to its function? (5 points)

Triglycerides are mainly used as energy storage molecules. They are good for this because:
1. The long hydrocarbon tails of fatty acids contain lots of chemical energy so a lot of energy is released when they are broken down. Therefore lipids contain twice as much energy per gram as carbohydrates.
2. They're insoluble so don't affect the water potential of the cell and cause water to enter by osmosis. The triglycerides clump together as insoluble droplets in cells because the fatty acid tails are hydrophobic so the tails face inwards, shielding themselves from water with their glycerol heads
3. Have high ratio of energy storing C-H bonds to C atoms so is an excellent energy store
4. Low mass: Energy so large amounts of energy stored in small space so animals carry less weight
5. High hydrogen: Oxygen atoms so release water when oxidised for desert animals


What are the lipids found in cell membranes called? (1 point)



Describe the structure of phospholipids (3 points)

Only have 2 fatty acids attached to glycerol as one is replaced by a phosphate group.
The phosphate group is hydrophilic (attracts water)
But the tails are hydrophobic (repels water)


How does the stucture of phospholipids relate to its function? (3 points)

Phospholipids make up the bilayer of cell membranes which contol what enters and leaves the cell
Their heads are hydrophilic and their tails are hydrophobic, so they form a double layer with their heads facing out towards the water on either side
The centre of the bilayer is hydrophobic, so water-soluble substances can't easily pass through it. The membrane acts as a barrier to those substances


How are phospholipids and triglycerides similar? (4 points)

Both are lipids
Both have glycerol
Both have fatty acids
Both have ester bonds


How are phospholipids and triglycerides different? (1 point)

Triglycerides have 3 fatty acids whereas phospholipids only have 2 as 3rd fatty acid is replaced by a polar hydrophilic phosphate group


How do lipids arrange themselves in water? (4 points)

Hydrophilic head of phospholipid molecule asscociates itself with water but hydrophobic tail does not.
Therefre hydrophilic head is closest to water and hydrophobic tail furthest away.
This forms a spherical structure called micelles
If not in globular form they form a phospholipid bilayer


Describe the emulsion test for lipids (3 points)

Shake the test substance with ethanol for a minute so that it dissolves
Pour the solution into water
If lipids are present a milky emulsion will show


3.1.4 Proteins

What are the monomers of proteins? (1 point)

Long chains of amino acids


How is a dipeptide formed? (1 point)

When two amino acids join together


How is a polypeptide formed? (1 point)

When more than two amino acids join together


What are proteins made up of? (1 point)

1 or more polypeptide chains


What are the functions of proteins? (8 points)

Structure e.g. collagen and keratin
Enzymes e.g. amylase
Some hormones e.g. insulin
Membrane transport
Mass transport e.g. haemoglobin
Cell recognition


What are amino acids? (4 points)

Are the monomers that form the polymers called polypeptides
Polypeptides join together to make proteins
There are 20 amino acids that occur natuarally in proteins
The fact that the same 20 occur in every living organism is proof for evolution


What is the structure of an amino acid? (5 points)

All have:
Central carbon atom
Amino group
Carboxyl group
Hydrogen atom
R (variable side) group

Only difderence is each amino acid has a different R group

/ / //
H ---- N ----C ---- C ---- OH
R group


Describe the R-group (3 points)

The R-group composition of each amino acid varies greatly
Each of the 20 amino acids has a different side chain structure
Side chains contain mainly hydrogen, carbon and oxygen but some amino acids have nitrogen atoms in R group


How are dipeptides and polypeptides formed? (2 points)

Formed through condensation reactions
A peptide bond is formed C-N


What is polymerisation? (1 point)

Where amino acids join by a series of condensation reactions


What is the primary structure of a protein? (1 point)

The sequence of amino acids in the polypeptide chain


What is the secondary structure of a protein? (2 points)

Weak hydrogen bonds form between the amino acids in the chain due to the O of the -C=O having a negative charge and the H of the -NH group having a positive charge and are slightly attracted to each other
This causes the chain to coil into an alpha helix or fold into a beta pleated sheet


What is the tertiary structure of a protein? (5 points)

The secondary structure is folded and coiled more to create a 3D structure
The structure is maintained by strong disulphide bridges/bonds between two molecules of the amino acid cysteine as the sulphur atoms bond
Also has ionic bonds between carboxyl and amino acid not involved in forming dipeptide bonds.
They are weaker than disulphide and easily broken as pH changes
Also has lots of hydrogen bonds which are easily broken


What is the quaternary structure of a protein? (2 points)

Large proteins made from many individual polypeptide chains bonded together
Includes non-protein (prosthetic) groups e.g. haem group


How are enzymes specialised for its function? (2 points)

Roughly spherical shaped due to tight folding of polypeptide chains
They’re soluble and often have roles in metabolism
e.g. digestive enzymes break down food molecules whilst other enzymes synthesise large molecules


How are antibodies specialised for its function? (3 point)

Involved in the immune response
Made up of two light polypeptide chains and two heavy polypeptide chains bonded together.
Antibodies have variable regions and the amino acid sequences in these regions vary greatly


How are transport proteins specialised for its function? (3 points)

Channel proteins are present in cell membranes. Contain hydrophobic and hydrophilic amino acids, which cause protein to fold up and form a channel.
These proteins transport molecules and ions across membranes


How are structural proteins specialised for its function? (3 points)

Are physically strong
Consist of long polypeptide chains lying parallel to each other with cross-links between them
Includes keratin and collagen


What are fibrous proteins? (2 points)

Have structural features
Form long chains which run parallel to each other
E.g. Collagen


What are globular proteins? (2 points)

Carry out metabolic functions
Not structural
E.g. Haemoglobin and enzymes


What is the function of collagen? (4 points)

Found in tendons.
Tendons join muscles to bones.
When a muscle contracts the bone is pulled in direction of contraction.
Collagen controls this


What is the structure of collagen? (4 points)

Primary structure = unbranched polypeptide chain
Secondary structure = Polypeptide chain very tightly wound. Lots of amino acid glycine helps close packaging
Tertiary structure = Chain is twisted into second helix
Quaternary structure = Made up of 3 polypeptide chains wound together


How does collagen’s structure relate to its function? (3 points)

Quaternary structure makes it suitable molecule for tendons as individual collagen polypeptide chains in fibres are held together by cross-linkages between amino acids of adjacent chains
Cross linkages increase strength and stability of collagen fibre as points where collagen molecule ends and next one starts are spread throughout fibre instead of in one place
Arrangement of collagen is necessary for efficient functioning of tendon because each polypeptide forms long, unfolded strand. Individual polypeptide strands are wound tightly around each other. Long fibrous molecular shape


What is the function of haemoglobin? (1 point)

Efficiently transports oxygen


What is the structure of haemoglobin? (4 points)

Primary structure = consists of 4 polypeptide chains
Secondary structure = In each of polypeptide chains is a coiled helix
Tertiary structure = Each polypeptide chain folded into precise shape to be able to carry oxygen
Quaternary = All polypeptide chains linked together to form spherical molecule


How does haemoglobin’s structure relate to its function? (3 points)

Readily associates with oxygen at the surface where gas exchange takes place
Readily dissociate from oxygen at tissues requiring it
Haemoglobin changes its affinity for oxygen because its shape changes in presence of certain substances due to having different amino acid sequences


Describe the biuret test for proteins (4 points)

Add a few drops of sodium hydroxide solution to food sample to make it alkaline
Then add some copper (II) sulphate solution
If protein is present the solution turns purple
If no protein is present, the solution stays blue


What are enzymes? (1 point)

Enzymes are proteins that speed up chemical reactions by acting as biological catalysts


What do enzymes do? (4 points)

Catalyse metabolic reactions both at a cellular level (e.g. respiration) and for the organism as a whole (e.g. digestion in mammals). Since they ae a catalyst they are not used up in the reaction

They lower the activation energy of a reaction which speeds up the rate of a reaction

Enzyme action can be intracellular or extracellular

Enzymes can affect structures in an organism (e.g. involved in production of collagen) as well as functions (e.g. respiration)


How do enzymes lower the activation energy? (2 points)

When a substrate fits into the enzymes active site it forms an enzyme-substrate complex which lowers activation energy because:

1. If two substrate molecules need to be joined, being attached to enzyme holds them close together, reducing repulsion between molecules so can bond more easily.
2. If the enzyme is catalysing a breakdown reaction, fitting into the active site puts a strain on bonds in the substrate, so the substrate molecule breaks up more easily


What is the structure of an enzyme? (4 points)

Enzymes are made from a long folded chain of amino acids so is a globular protein
Hydrogen bonds hold the chain in the correct shape
DNA dictates the order in which amino acids join
The different amino acids fold in different ways to give enzymes a specific shape


How does enzyme specificity work? (2 points)

A specific and complementary substrate binds to an enzymes active site to form an enzyme-substrate complex.
The enzyme then breaks down the substrate to form the products of the reaction


What is the Lock and Key hypothesis? (3 points)

Outlines that the substrate fits into the enzyme in the same way a key fits into a lock
It correctly identifies concept of active site where substrate binding and catalysis occurs
Explains specificity of enzymes for particular substrates


What are the limitations of the Lock and Key hypothesis? (2 points)

Does not fully explain how products are released
Does not explain why some enzymes act on a small number of similar substrates


What is the Induced Fit Model? (3 points)

This shows that the active site changes shape as substrates bind at the same time causing a change in the shape of the substrate
This results in a tight fit where the active site is now complementary to the altered substrate
The change in substrate shape induces strain in the substrate bonds which lowers the activation energy required for the reaction to occur by lowering the amount of energy needed to break the bonds in the substrate


How does temperature affect enzyme function? (5 points)

As temperature increases, kinetic energy of the enzymes molecules increases.
The molecules move faster and collide more often. Enzymes and substrates successfully collide more often creating more enzyme-substrate complexes.
If the temperature increases above 37˚C the molecules vibrate more which breaks some of the bonds holding the enzyme in shape.
The enzymes active site loses its shape and the enzyme becomes denatured as the enzyme and substrate no longer fit together.


How does pH affect enzyme function? (2 points)

Altering the pH causes a change in charges on amino acids that form active site so substrate can no longer attach to active site, so enzyme-substrate complexes are not possible
Changing pH can break the ionic bonds involved in enzymes tertiary structure which causes a change in shape of active site so the substrate can no longer fit, and the enzyme is denatured


How does substrate concentration affect enzyme function? (3 points)

At low substrate concentration, rate of reaction is slow as there are too few substrate molecules to fill all enzyme active sites so there is a limited number of collisions and enzyme-substrate complexes that can form.
As substrate concentration increases, rate of reaction increases up to a point. There are more substrate molecules so more chances of collisions, so more enzyme-substrate complexes formed, and more products released
At high substrate concentrations, rate levels off as reaction is proceeding as fast as possible but addition of extra substrate molecules doesn’t make difference as active sites are fully occupied only addition of enzymes increase rate


How does enzyme concentration affect enzyme function? (3 points)

As enzyme concentration increases, rate of reaction increases as due to having more enzyme molecules in the solution it is more likely a substrate molecule will collide with an active site and form an enzyme-substrate complex.
Plateau (Vmax) occurs when the number of substrates is limited so no more collisions occur.
To increase rate more substrates must be added


What is Vmax? (1 point)

When the rate of reaction is at its maximum as all available active sites have been occupied at one time


What is competitive inhibition? (4 points)

When molecules have a similar shape to substrate molecules so compete with the substrate molecules to bind to active site, but no reaction takes place.
Instead they block the active site so no substrate molecules can fit in it.
If there's a high concentration of inhibitor it'll take up nearly all active sites and hardly any of substrate will bind to the enzyme
If there's a higher concentration of substrate then it is easier for the substrate to bind to the active site so increasing concentration of substrate will increase rate up to a point


What is non-competitive inhibition? (4 points)

When molecules bind to the enzyme away from its active site.
This causes the active site to change shape so the substrate molecules can no longer bind to it.
They don't compete with the substrate molecules to bind to active site as they are different shape. Increasing concentration of substrate won't make difference to reaction rate as enzyme activity will still be inhibited











3.1.5 Nucleic acids

What is DNA? (2 points)

DNA is a polymer of repeating nucleotides (a polynucleotide)
Scientific name is DeoxyriboNucleic Acid


What does DNA contain? (1 point)

Genetic information to make new cells, control their function and make proteins


Where is DNA found? (2 points)

Nucleus of a cell contains chromosomes which are made of genes which are sections containing DNA.
Genes are sections of DNA which code for different proteins and different characteristics as a result


What is DNA made from? (1 point)

Two polynucleotide chains twisted around each other and held together with hydrogen bonds


What is the structure of a mononucleotide? (1 point)

A deoxyribose pentose sugar attached to a phosphate group and an organic nitrogenous base


What bond joins the pentose sugar and phosphate group? (1 point)

Ester bond - 1st of the 2 condensation reactions occuring to release water


What bond joins the pentose sugar and organic base? (1 point)

Glycosidic bond - 2nd of the 2 condensation reactions occurng to release water


How is a polynucleotide formed? (2 points)

Many nucleotides join together to form a polynucleotide
A condensation reaction occurs between the sugar of one mononucleotide and phosphate group of another


What is the sugar phosphate backbone? (1 point)

The bonded sugar of one mononucleotide and phosphate group of another


What is the bond between sugar of one mononucleotide and phosphate of another called? (1 point)

Phosphodiester bond


What are the 4 possible bases of DNA? (4 points)



What is complementary base pairing in DNA? (3 points)

A pairs with T and has 2 hydrogen bonds
C pairs with G and has 3 hydrogen bonds
A and T, C and G should have equal amounts


Structure and function of DNA (4 points)

S: DNA molecule is very long
F: Stores lots of information

S: Two strands are complementary
F: Each starnd acts as a template for copying the other

S: Two strands are held together by hydrogen bonds
F: It is easy to separate the strands to transcribe the genes and replicate the DNA

S: The bases are located on the inside of double helix
F: The bases are partly protected from damage by free radicals


How is DNA a stable molecule? (2 points)

The phosphodiester backbone protects the more chemically reactive bases
Hydrogen bonds join the bases forming bridges between the 2 phosphodiester uprights


What is RNA? (2 points)

A polymer of nucleotides
So has a pentose sugar attached to a phosphate group and a nitrogenous base


What are the three types of RNA and their roles? (3 points)

1. Messenger RNA (mRNA) - are copies of DNA produced in transcription that leave the nucleus through pores in membrane and give instructions to the ribosomes
2. Ribosomal RNA (rRNA) - makes up part of the ribosome structure (the rest is made of protein)
3. Transfer RNA (tRNA) - used to carry specific amino acids during the process of protein synthesis called translation


Describe the process of protein synthesis (6 points)

1. DNA helicase unzips the DNA molecule (breaks hydrogen bonds between bases)
2. mRNA takes a copy of the DNA template strand (transcription inside of nucleus)
3. mRNA leaves the nucleus through a nuclear pore
4. The ribosome attaches to the mRNA
5. tRNA molecules attach their complementary anti-codon which is attached to an amino acid (translation outside of nucleus)
6. Each amino acid joins together to form a polypeptide


How is DNA different from RNA? (5 points)

1. DNA has a deoxyribose sugar present whereas RNA has a ribose sugar
2. DNA is structured as a double helix whereas RNA is single stranded
3. DNA has complementary base pairing Adenine with Thymine, Cytosine with Guanine whereas RNA has no base pairing and Thymine is replaced with URACIL
4. DNA is a larger and longer molecule whereas RNA is shorter and smaller
5. In DNA you can predict the percentage of bases present as A and T, C and G are equal whereas in RNA you cannot predict the percentage of other bases from percentage of 1 base


What is DNA replication vital for? (3 points)



What is conservative replication? (1 point)

The original DNA double helix replicates to produce a newly synthesised material stranded double helix and an original parental DNA stranded doule helix


What is dispersive replication? (1 point)

The original DNA double helix replicates to produce two double helixes each with each strand having parental DNA interspersed between two daughter molecules


What is semi-conservative replication? (2 points)

The original DNA double helix replicates to produce two DNA double helices each double strand has one parental and one new strand
This is the main theory we use today for DNA replication


Describe the process of semi-conservative replication? (4 points)

1. The enzyme DNA helicase breaks the hydrogen bonds between bases on the two polynucleotide DNA strands which makes the helix unwind to form two single strands
2. Each original single strand acts as a template for a new strand. Complementary base pairing means that free-floating DNA nucleotides are attracted to their complementary exposed bases on each original template strand
3. Condensation reactions join the nucleotides of the new strands togeher by hydrogen bonds forming between bases on original and new strands to form a polynucleotide chain with a phosphodiester bond and strong sugar phosphate backbone formed (polymerisation). Catalysed by enzyme DNA polymerase
4. Each new DNA molecule contains one strand from original parental DNA molecule and one new strand


What is needed for DNA replication? (5 points)

DNA helicase to break apart strands
Free nucleotides to synthesise new strand
DNA template
DNA polymerase to re-synthesise backbone


Why does DNA polymerase move down the template strand in a 3' to 5' direction? (5 points)

Each end of a DNA strand is slightly diferent in its struture.
In a DNA helix the strands run the opposite way (antiparallel)
The active site of DNA polymerase is only complementary to 3' prime end so enzyme only adds nucleotides to the new strand at the 3' end so the new strand is made in a 5' to 3' direction.
Therefore the DNA polymerase moves down the template strnd in 3' to 5' direction
Because the strands in DNA double helix are anti-parallel, the DNA polymerase working on one of template strands moves in opposite direction to DNA polymerase working on other


Describe Meselson and Stahl's method for proving DNA replication only happens via semi-conservative replication (6 points)

1. Two samples of bacteria were grown - one in nutrient broth containing light nitrogen (N14) and one in broth containing heavy nitrogen (N15). As the bacteria reproduced, they took up nitrogen from the broth to help make nucleotides for new DNA. So the nitrogen gradually became part of the bacteria's DNA
2. A sample of DNA taken from each batch of bacteria and spun in centrifuge. DNA from heavier nitrogen bactria settled lower down he centrifuge tube than DNA from light nitrogen because its heavier
3. Bacteria grown in heavy nitrogen broth taken out and put in broth containing only light nitrogen. Bacteria left for one round of replication and then another sample of DNA taken out and spun in centrifuge
4. If replication was conservative the original heavy DNA which would still be together would settle at bottom and new light DNA settle at top
5. If replication semi-conservative new bacterial DNA molecules would contain ne strand old DNA with heavy nitrogen and one new with lighter nitrogen. So DNA would settle out between where light and heavy settle
6. However DNA settled in middle showing that DNA contained a mixture of heavy and light nitrogen so bacterial DNA had replicated semi-conservatively


3.1.6 ATP

What is ATP called? (1 point)

Adenosine Triphosphate


What is the structure of ATP? (3 points)

A molecule of Ribose
A molecule of Adenine
Three Phosphate groups


Why is ATP known as a nucleotide derivative? (1 point)

It's a modified form of a nucleotide


How does ATP act as the immediate source of energy in a cell? (6 points)

Plant and animal cells release energy from glucose through respiration
A cell can't get its energy directly from glucose
So, in respiration the energy released from glucose is used to make ATP
Once made, ATP diffuses to the part of the cell that needs energy
The energy in ATP is stored in high energy bonds between the phosphate groups.
Energy is released via hydrolysis reactions


Describe the process of hydrolysis of ATP (3 points)

When energy is needed by a cell, ATP is broken down into ADP (adenosine diphosphate) and Pi (inorganic phosphate)
A phosphate bond is broken and energy released
The reaction is catalysed by the enzyme ATP hydrolase


What does hydrolysis of ATP require? (2 points)

ATP hydrolase


What does hydrolysis of ATP produce? (3 points)

Inorganic Phosphate Group


What is the energy released used for? (8 points)

Cellular reactions that are endergonic
e.g. Active Transport
Movement and Muscle contraction
Breakdown and synthesis of new molecules
Enzyme controlled reactions
e.g. Respiration
e.g. Photosynthesis
e.g. Digestion


How can ATP hydrolysis be coupled to other energy-requiring reactions? (1 point)

The energy released can be used directly to make the coupled reaction happen, rather than being lost as heat


How can the released inorganic phosphate be used? (1 point)

It can be added to another compound (known as phosphorylation) which makes the compound more reactive


Describe the process of re-synthesis of ATP (2 points)

A condensation reaction occurs between ADP and Pi
Process is catalysed by enzyme ATP synthase


What does re-synthesis of ATP require? (2 points)

ATP synthase


What does re-synthesis of ATP produce? (1 point)

Adenine Triphosphate


Where does re-synthesis occur? (2 points)



Where does the energy to synthesise ATP come from? (1 point)

Catabolic reactions that are exergonic


Where is ATP found? (1 point)

In mitochondria of all cells


3.1.7 Water

What is the structure of water?

A molecule of water (H2O) is made up of 2 atoms of hydrogen and one atom of oxygen by shared electrons


How is water a polar molecule? (3 points)

It has a partial negative charge on one side and a partial positive on the other
Slight positive charge is caused by due to the shared negative hydrogen electrons being pulled towards the oxygen atom, the other side of hydrogen is left with positive charge
Slight negative charge is caused by the unshared negative electrons on the oxygen atom


What is hydrogen bonding in water? (1 point)

When the slightly negatively-charged oxygen atoms attract the slightly positively-charged hydrogen atoms of other water molecules


What are the properties of water? (8 points)

Surface tension
High specific heat capacity/Temperature buffer
High latent heat of vaporisation


Explain the property of surface tension and its biological importance (2 points)

Surface tension is the uneven distribution of force at a boundary interface caused by molecular bonding
The surface of water forms a skin which is strong enough to support small aquatic animals


Explain the property of density and its biological importance (3 points)

Density is a measure of mass per unit of volume
Because water freezes from top down, organisms are able to survive below surface of ice which acts as insulating layer.
Changing density maintains circulation in large bodies of water to help nutrient cycling


Explain the property of water being a solvent and its biological importance (3 points)

A solvent is a liquid substance which can dissolve a wide range of molecules
It allows water to act as a transport medium for polar molecules causing them to dissociate as the positive end of water is attracted to negative ion and negative end of water attracted to positive ion so ions are totally surrounded by water and dissolve
It also removes metabolic wastes such as urea and ammonia


Explain the property of high specific heat capacity/being a temperature buffer and its biological importance (3 points)

Specific heat capacity is the amount of heat required to raise 1kg of water by 1°C. High means it requires a lot of energy
This is crucial for living organisms which need to maintain particular temperatures in order to optimise enzyme activity.
High water content of cells and tissues helps them to maintain a constant temperature. In this way water acts as a temperature buffer


Explain the property of cohesion and its biological importance (3 points)

Cohesion is the tendency of molecules of a substance to attract one another
Water molecules are very cohesive because they are polar which helps water flow, so water is good for transporting substances
The cohesion allows water to move up the xylem


Explain the property of adhesion and its biological importance (3 points)

Adhesion is the tendency of molecules to be attracted to other molecules of a different type
A strong force of attraction between the water molecules and the walls of the xylem allow transpiration to take place.
This is what causes water to be wet


Explain the property of high latent heat of vaporisation and its biological importance (2 points)

High latent heat of vaporisation means it requires a lot of energy to break hydrogen bonds between water molecules when water evaporates
This is useful for living organisms as it means they can use water loss through evaporation to cool down without losing too much water


Explain the property of water being an important metabolite and its biological importance (3 points)

Many metabolic reactions involve condensation or hydrolysis reactions
Hydrolysis requires a molecule of water to break a bond e.g. energy from ATP released through hydrolysis reaction
Condensation releases a molecule of water when a new bond is formed e.g. amino acids are joined to make polypeptides (proteins) by condensation reactions


3.1.8 Inorganic ions

What are ions? (3 points)

An atom or molecule that carries an electric charge
An ion with positive charge is called a cation
An ion with negative charge is called an anion


What is an inorganic ion? (1 point)

An ion which does not contain carbon


What is the main role of hydrogen ions? (2 points)

Buffering the blood
Controlling/altering pH (pH measured in units of moles per litre of hydrogen ions)


How is hydrogen important for normal physiological functions? (4 points)

Proteins require optimum pH
Proteins denature in incorrect pH
Enzymes required for metabolic activities
Channel proteins required for movement of ions and waste


How are iron ions important? (4 points)

Involved in several biological processes such as: - A component of
- Involved in the
electron transport
chain in respiration
Haemoglobin is a large protein that carries oxygen around the body, in the red blood cells
It’s made up of 4 different polypeptide chains, each with an iron ion (Fe²⁺)
The Fe²⁺ binds to the oxygen in haemoglobin


How are sodium ions important? (1 point)

Sodium ions are important in the control of glucose and amino acids moving in or out of the cell in co-transport


How are phosphate ions important? (4 points)

DNA, RNA and ATP all contain phosphate groups
The bonds between phosphate groups store energy in ATP
The phosphate groups in DNA and RNA allow nucleotides to join up to form polynucleotides
Phospholipids are important in cell membrane


How are other examples of inorganic ions important? (3 points Calcium, magnesium and nitrates)

Calcium is useful for strong bones and teeth and glue sticking plant cells together
Magnesium is a component of chlorophyll and minerals in bones and teeth
Nitrates are important in protein-synthesis in plants and nitrogenous bases in nucleotides