Module 2: Biological Molecules

Question 1

Condensation reaction

Answer 1

Links monomers together

A water molecule is released
A covalent bond is formed
A larger molecule is formed

Question 2

Hydrolysis reactions

Answer 2

Splits molecules apart

A water is used
A covalent bond is broken
Smaller molecules are formed

Question 3

Hydrogen bonds

Answer 3

Hydrogen bonds hold polymers in shape. This shape allows them to carry out a function.

Hydrogen bonds form when a slightly negative and a slightly positive charge come class together.

They are weak and easily broken

Question 4

What are carbohydrates made up of?

Answer 4

C, H and O

For every one carbon there are two hydrogens and one oxygen

Simple sugars= monosaccharides

• contain 3-6 carbons
• soluble in water
• sweet tasting
• form crystals

Question 5

Carbohydrates- disaccharides

Answer 5

2 monosaccharides will join in a condensation reaction to form a disaccharide.

We call this covalent bond between monosaccharides a glycosidic bond.

Question 6

a and B glucose

Answer 6

ADD PICTURE

Question 7

Carbohydrates- storage

Answer 7

Plants and animals are only capable of breaking down a glucose, not B glucose due to the difference in structure.
B glucose can’t be respired so they are not used for storage.

Question 8

Polysaccharides- Amylose

Answer 8

a glucose + a glucose= maltose (disaccharide)

This reaction occurs thousands of times to form amylose.

The a glucose molecules are held together by a 1-4 glycosidic bond.

Amylose forms a spring shape due to the shape of glucose and glycosidic bonds.

Amylose is unbranched an compact. It is insoluble.

Question 9

Polysaccharides- Starch

Answer 9

Plant energy storage:

Starch is a mixture of amylose molecules and amylopectin molecules.

Amylopectin- branches of a glucose chains with 1-4 glycosidic bonds joined at ends to another chain by a 1-6 glycosidic bond.

It is a store of energy because it can be broken down into a glucose by enzymes in hydrolysis reactions.

Question 10

Polysaccharides- Glycogen

Answer 10

Animal energy storage:

Polysaccharide of a glucose

• Glycogen is broken down by enzymes in hydrolysis reactions to form glucose for respiration.
• Found in glycogen granules in animal cells e.g. in live and muscles
• More compact than starch

1-4 linked chains are shorter and more branched than 1-6 chains (starch)

More branches= more ends to be broken off= faster break down= faster energy release

Question 11

Starch and glycogen similarities

Answer 11

Insoluble in water- don’t reduce the water potential in cells.

Store glucose molecules in chains so they can be easily broken off and the glucose can be used in respiration.

Question 12

Cellulose

Answer 12

Cellulose is a structural unit found in plant cell walls.

Polysaccharide of 1000s of B glucose joined together by condensation reactions. Forms with 1-4 glycosidic bonds in a long, straight, unbranched chain.

Every B glucose is flipped 180 degrees to form a glycosidic bond.

Hydrogen bonds form between neighbouring cellulose chains and the chains become cross-linked to form a microfibril. Microfibrils are held together by hydrogen bonds to form macrofibrils.

• Micro and macrofibrils control cell shape.
• Macrofibril arrangement in guard cells cause the opening and closing of stomata.

Question 13

Macrofibrils

Answer 13

Macrofibrils are embedded with pectin which glues them together in a criss-cross structure to form cell walls.

The criss-cross structure allows water to pass through- Macrofibrils are very strong so that water moving in doesn’t cause them to burst.

Question 14

Other Carbohydrate Polymers are used by a number of other organisms to provide support. For example…

Answer 14

Chitin- insect exoskeleton

Peptidoglycan- bacterial cell walls

Question 15

What are amino acids?

Answer 15

Monomers of proteins

There are 20 different amino acid- each have a different R group.

Amino acids are joined together through a condensation reaction. The covalent bond formed is called a peptide bond.

2 amino acids joined= dipeptide

A polymer of amino acids is called a polypeptide (protein)
The backbone will always have the same pattern:
NCC,NCC,NCC,NCC,NCC…

Peptide bonds are broken through a hydrolysis reaction.
Dipeptides are broken down into 2 amino acids. When proteins are digested, hydrolysis reactions break apart the amino acids.

Question 16

Function of proteins

Answer 16

Proteins are polymers of amino acids.

Functions:

• Structural- muscle & bone
• Protein channels
• Enzymes
• Many hormones
• Antibodies

Proteins are crucial for growth and repair and metabolic activity.

Question 17

Making proteins…

Answer 17

To make proteins organisms need amino acids.

Plants make their own using nitrates in the soil.

Animals need to consume protein in their diet. The polypeptide is broken down in digestion and built back up again to make protein for the body.

Question 18

Primary structure of proteins

Answer 18

Every protein has a different sequence of amino acids- this is it’s primary structure.

This determines it’s structure which determines it’s properties and function.

Question 19

Breaking apart proteins

Answer 19

Enzymes that beak apart peptide bonds are proteases.

E.g. digestion, hormones so that their effect isn’t constant.

Question 20

Transcription- GCSE understanding

Answer 20

Taking the DNA code and making messenger RNA (mRNA).

1) An enzyme unwinds the double helix of DNA.
2) The two strands are separated so that free nucleotides can fit in.
3) Free nucleotides attach to he complementary base pairs.
4) mRNA moves away from the DNA helix and another enzyme zips the strands together.
5) The mRNA is small enough to leave the nuclear membrane.

Question 21

Translation- GCSE understanding

Answer 21

Taking the message from mRNA and translating it into a chain of amino acids.

1) The mRNA enters the ribosome.
2) Transfer RNA (tRNA) enters the ribosome and brings with it a specific amino acid that corresponds with the codon on the mRNA strand.
3) tRNA has an anti-codon that matches the codon on mRNA so they pair together using complementary base pair rules.
4) The amino acid that is brought by the first tRNA binds to the second amino acid by a peptide bond.
5) When all the amino acids have been joined together, the mRNA leaves the ribosome and a new protein has been made.

Question 22

Secondary structure of proteins

Answer 22

As polypeptides form, to prevent them from tangling they are stabilised by being coiled (alpha helix) or pleated (beta pleated sheet). These are held in place by hydrogen bonds. This coiling/pleating is the proteins secondary structure.

Question 23

Why is the secondary structure dependent on the primary structure?

Answer 23

The primary structure of a protein is a sequence of amino acids.

Different proteins have different sequence of amino acids which have different R groups with different properties.

These different properties mean that hydrogen bonds form in different places of the pleats/coils meaning that some or more/less pleated/ coiled than others.

Question 24

Tertiary structure of proteins

Answer 24

The tertiary structure of a protein is the overall 3D structure of the protein.

This is when the coil/pleat coils or folds into the final shape (this folding is dependant on the primary structure).

The tertiary structure is key to the protein’s function (e.g. hormone needs to fit into complementary receptor/enzyme’s active site).

Question 25

The tertiary structure is maintained by different bonds

Answer 25

1) Disulfide bonds- The amino acid cysteine contains sulfur. Where two cysteines are found close to each other a covalent bond can form.
2) Ionic bonds- R groups sometimes carry a charge. Where oppositely charged amino acids are found close together an ionic bond forms.
3) Hydrogen bonds- Where slightly positive groups are found close to slightly negative groups, hydrogen bonds form.
4) Hydrophobic and hydrophilic interactions in a water-based environment, hydrophobic amino acids will be most stable if they are held together with water excluded. Hydrophilic amino acids tend to be found on the outside of globular proteins, with hydrophilic in the centre.

Question 26

Globular and Fibrous proteins

Answer 26

Globular proteins have molecules of a spherical shape.
Any hydrophobic R groups are turned inwards towards the centre of the molecule, while hydrophilic groups are on the outside. This makes the protein soluble in water, because water can easily cluster around them and bind to them. They often have very specific shapes, which helps them to take up roles as enzymes, hormones and haemoglobin.

Fibrous proteins has a long, thin structure and are usually insoluble in water and metabolically inactive, often having a structural role in an organism. Examples include collagen, elastin and keratin.

Question 27

Denaturation

Answer 27

Heat energy gives molecules kinetic energy. Kinetic energy makes molecules vibrate and can break bonds.

Heating proteins can break the bonds holding their tertiary structure in place ‐ this changes the shape of the protein. This is called denaturing.

The shape of a protein is vital to its function so once the bonds are broken and its tertiary structure is lost, the protein will no longer function properly.

(Colvalent bonds are very strong so need more heat energy to break them).

Question 28

Haemoglobin

Answer 28

Haemoglobin has a quaternary structure with 4 subunits ‐ 2 α‐chains and 2 β‐chains each with a prosthetic (non amino acid) haem group.

primary structure: sequence range of amino acids
secondary structure: mostly alpha helices
tertiary structure: alpha chains and beta chains
quaternary structure: 2 alpha and 2 beta chains

Question 29

Globular and Fibrous proteins comparison

Answer 29

…

Question 30

Collagen structure

Answer 30

Collagen molecules’ quaternary structure are made up of 3 polypeptide chains tightly wound around each other ‐ hydrogen bonds between them gives the molecule strength.

Every 3rd amino acid on each polypeptide chain is a glycine. These are small and allow close packing.

Covalent bonds cross link parallel collagen molecules.
This forms a collagen fibril. The ends of molecules and covalent bonds are staggered to add strength. Many fibrils form a collagen fibre.

Question 31

Function of collagen

Answer 31

• lines arterial walls ‐ prevents blood at high pressure bursting walls
• tendons ‐ all muscles to pull bone for movement
• bones ‐ collagen reinforced with other materials to make them hard
• cartilage and connective tissue
• cosmetic treatments ‐ collagen injections can make lips look fuller.

Properties for function:

• High tensile strength
• Not elastic
• Flexible
• Insoluble

Question 32

Collagen Vs Cellulose

Answer 32

…

Question 33

What is a lipid?

Answer 33

A lipid dissolves in organic solvents (alcohol) but not water.
They include triglycerides, phospholipids, glycolipids, cholesterol.

Solid lipid= fat
Liquid lipid= oil

Question 34

Role of lipids in organisms

Answer 34

• Energy source
• Energy store ‐ lipids stored in adipose cells
• Phospholipid bilayers
• Thermal insulation
• Myelin sheath of neurones ‐ electrical insulation
• Steroid hormones
• Waxy cuticle of leaves ‐ prevents drying out

Question 35

Triglyceride structure

Answer 35

Triglycerides are made up of glycerol and fatty acids.

Glycerol has 3 carbons and has free -OH groups , which are important to the structure of triglycerides.

Fatty acids have a carboxyl group (-COOH) on one end, attached to a hydrocarbon tail made of only carbon and hydrogen atoms. This may be anything from 2-20 carbons long.

Question 36

Saturated and unsaturated fatty acids

Answer 36

If a fatty acid is saturated this means that there are no C=C bonds in the molecule.
If a fatty acid is unsaturated, there is a C=C bond between two f the carbons, which means fewer hydrogen atoms can be bonded to the molecule.

A single C=C make the fatty acid monounsaturated.
- Oleic acid
More than one C=C bond makes it polyunsaturated.
- Linoleic acid

Having one or more C=C bonds changes the shape of the hydrocarbon chain, giving it a kink where the double bond is. Because these kinks push the molecules apart slightly, it makes them more fluid.