Biology - Biological molecules & Nucleic Acids

What is a monomer?

Smaller units of which larger molecules are made up of

What is a polymer?

Molecule made of lots of repeating units joined together

What is a condensation reaction

When 2 monomers join together and form a covalent bond with the elimination of a water molecule

What is a hydrolysis reaction

Breaking the covalent bond between monomers with the addition of a water molecule

What is an isomer

Compounds with the same chemical formula but different structural arrangements

What is a disaccharide

Two monosaccharide join via a condensation reaction and form a glycosidic bond

State the structure, properties and uses of starch

• alpha glucose

• Amylopectin → 1-4 and 1-6 glycosidic bonds, long branched chains which increase the SA so it can hydrolyse glycosidic bonds

• Amylose → 1-4 glycosidic bonds, long unbranched chains. Has coils so it can hold more in small space

• Uses → excess glucose store (plants), insoluble so doesnt affect water potential, energy store, large so doesn’t diffuse out of cells

State structure, properties and uses of glycogen

• alpha glucose

• 1-6 glycosidic bonds, long branched chains which increase the SA so it can hydrolyse glycosidic bonds

• Uses → excess glucose store, energy store, insoluble so doesnt affect water potential, large so doesnt diffuse out of cells

State structure, properties and uses of cellulose

• beta glucose

• long unbranched chains, 1-4 glycosidic bonds.

• alternate glucose molecules are rotated 180°

• cellulose chains linked together by hydrogen bonds between glucose molecules make microfibrils

• microfibrils are strong and flexible bc of hydrogen bonds between cellulose

• Uses → supports cell walls

Explain how cellulose molecules are adapted for their function in plant cells. (3)

• Long and straight cellulose chains

• Are held together by hydrogen bonds to make microfibrils

• Which provide strength

Compare and contrast the structure of starch and the structure of cellulose. (6)

• Both polysaccharides, both have glycosidic bonds, both contain C,H,O

• Cellulose has microfibrils and starch doesn’t

• Starch is alpha glucose and cellulose is beta glucose

• Starch contains two types of molecules and cellulose contains one

What is the test for sugars ?

• Reducing → Benedicts solution

• Add benedicts solution to sample, then heat in water bath above 80°

• Blue → green, orange, yellow, brick-red

• Non-reducing → Add dilute HCl then heat in waterbath to break bonds, then add alkali to neutralise

• Add benedicts solution, then heat in water bath above 80°

• Blue → green, orange, yellow, brick-red

What is the test for starch ?

• Iodine

• Browny-orange to blue-black

What are the roles of lipids ?

• energy source

• waterproofing

• protects organs

• forms hormones and membranes

• insulates organisms & myelin

How is triglyceride function linked to its structure ?

• high C-H bonds → good energy source

• insoluble → doesn’t affect water potential

• low mass → more energy stored in small vol.

State structure of a phospholipid

• One glycerol molecule, one phosphate group, two fatty acid chains joined together by ester bonds

• Phosphate head is hydrophilic and points outwards - towards water

• Fatty acid tails are hydrophobic and face inwards - away from water

• forms phospholipid bilayer

State structure of a triglyceride

• glycerol and three fatty acid chains joined via ester bonds

• non-polar, fatty acid tails are hydrophobic so its insoluble

• uses: energy store

Difference between saturated and unsaturated fatty acids?

Saturated → no double C-C bonds, maximum amount of hydrogen atoms

Unsaturated → one double C-C bond, fewer hydrogen atoms and double C-C bond causes bend

What is the test for lipids ?

• Add ethanol and then water and shake

• Milky white emulsion forms

What is a dipeptide

Two amino acids join via condensation reaction, forming a peptide bond between their carboxyl and amine groups

What is the primary structure

• sequence of amino acids in polypeptide chain

• determines the shape and function

• peptide bonds

What is the secondary structure

• alpha helix or beta pleated sheets held by hydrogen bonds

What is the tertiary structure

• 3d shape of the polypeptide chain

• maintained by weak hydrogen bonds, ionic bonds and strong disulfide bridges

What is the quaternary structure ?

• multiple polypeptide chains joined together

What is the test for proteins ?

• Add Biuret test and shake

• Turns from blue to lilac

What is an enzyme?

• biological catalyst that speeds up reactions by lowering activation energy

• specific tertiary structure determines shape of active site, complementary to a specific substrate

• can form enzyme-substrate complexes because its active site is complementary

What is the Lock and Key Model ?

States that the enzyme active site is exactly complementary to the substrate and the substrate fits exactly when forming an ES complex

What is the Induced-fit Model?

States that the enzyme’s active site is not exactly complementary to the substrate and changes shape to become complementary in order to form an ES complex

What are the factors affecting enzyme action ?

• enzyme concentration

• substrate concentration

• temperature and pH

How does enzyme concentration affect enzyme action

• more active sites for substrate to bind to so more ES complexes form

• substrate concentration becomes limiting factor

How does substrate concentration affect enzyme action

• more frequent collisions so more ES complexes form

• enzyme concentration becomes limiting factor

How does temperature affect enzyme action

• kinetic energy increases so more frequent collisions and more ES complexes form

• at extreme temps, enzyme denatures and bonds that maintain tertiary structure break so no more ES complexes can form as active site is no longer complementary

How does pH affect enzyme action

• at extreme pH’s, the enzyme denatures and no ES complexes can be formed as the active site changes shape

What is a competitive inhibitor

• similar shape to the substrate

• binds to active site and blocks substrate from binding so no ES complexes are formed

What is a non competitive inhibitor

• binds to the enzyme’s allosteric site which changes the shape of the active site so no ES complexes can form

what is DNA made up of

• one phosphate group, nitrogenous base and deoxyribose sugar

• nucleic acids (DNA) are made up of nucleotides

• nucleotides bind together via condensation reactions and form phosphodiester bonds (between phosphate group of one nucleotide and deoxyribose sugar on other nucleotide)

describe the bases in a nucleotide

• adenine and guanine are purines (two ring structure)

• thymine and cytosine are pyrimidines (one ring structure)

• bases join via complementary base pairing

• adenine and thymine form 2 hydrogen bonds

• cytosine and guanine form 3 hydrogen bonds

how does DNA structure relate to the function

• large molecule → carries lots of genetic information

• weak hydrogen bonds → easily hydrolysed during replication

• complementary base pairing → so identical copies can be made

describe the structure of ATP

• ribose sugar, nitrogenous base adenine and 3 inorganic phosphate groups

how is ATP made

• ATP is made during respiration from condensation reaction between ADP and inorganic phosphate, hydrolysed by ATP synthase

• ATP can be hydrolysed into ADP + inorganic phosphate

state 5 properties of ATP which makes it a good energy source

• ATP releases small amounts of energy so no energy is wasted

• small and soluble

• hydrolysis of 1 hydrogen bond is quick so energy release is fast

• transfers energy by transferring phosphate groups which makes other molecule more reactive

• it cant leave cell so provides immediate source of energy

how does DNA replicate

1. DNA helicase unzips strands by breaking hydrogen bonds

2. Each strand acts as a template for formation of new strands

3. Free nucleotides attach to template strands via complementary base pairing

4. DNA polymerase joins strands by forming phosphodiester bonds in backbone

5. DNA replication is semi-conservative because new strands are made from one old & one new strand

structure of water (polarity)

water is a dipole molecule so hydrogen bonds form between hydrogen⁺ and oxygen^-

properties of water

• metabolite - used in chemical reactions such as hydrolysis and condensation

• solvent - dissolves substances so they can be transported easier (allows transport of molecules)

• high specific heat capacity - lots of energy needed to increase temperature due to hydrogen bonds so it buffers changes in temp.

• large latent heat - lots of energy needed to change state due to hydrogen bonds so it provides cooling effect

• cohesion - hydrogen bonds mean water can stick together so water moves up xylem as column and provides surface tension so small organisms can live on surface

Describe the role of iron, sodium and phosphate ions in cells (5)

• Iron ions → haemoglobin binds to oxygen

• Sodium ions → co-transport of glucose into cells, as Na⁺ ions exit epithelial cell to bloodstream via active transport, creating concentration gradient for Na⁺ to enter via facilitated diffusion

• Phosphate ions → make ATP, phosphorylate other compounds which makes them more reactive