Biology - Chapter 1: biological molecules

Monomer

A smaller unit that can create large molecules

Polymer

A molecule made form a large number of monomers joined together

Examples of monomers

• Monosaccharides

• Amino acid

• Nucleotide

Examples of polymers

• starch

• Glycogen

• Cellulose

• Protein

• DNA

• RNA

Examples of monosaccharides

• Glucose

• Fructose

• Galactose

Examples of Disaccharides

• sucrose

• Maltose

• Lactose

Examples of polysaccharides

• starch

• Glycogen

• Cellulose

Definition of isomer

Same molecular formula different molecular structure

The structure of alpha glucose and beta glucose

The molecular formula is C6H12O6

Definition of disaccharides

Made of two monosaccharides joined together by a glycosidic bond formed via a condensation reaction

disaccharides reaction

• Glucose + glucose —> maltose + water

• Glucose + fructose —> sucrose + water

• Glucose + galactose —> lactose + water

Definition of condensation reaction

Bonding of two molecules fining a new chemical whilst removing water as a product

definition of hydrolysis reaction

Breaking of a chemical bond between two molecules using a water molecule

Definition of polysaccharides

Created by condensation reactions between many glucose monomers

Types of polysaccharides

Starch - in plant - store of glucose

Cellulose - in plant - structural strength in the cell wall

Glycogen - in animals - stores of glucose

Starch

Monomer - alpha glucose

Bonds between the monomers - 1,4 glycosidic bonds in amylose, 1,4 and 1,6 in amylopectin

Function - stores glucose

Location - plant cells (chloroplast)

Structure - made of 2 polymers: amylose - unbranched helix and amylopectin - a branched molecule

How the structure leads to the function?

• Helix can be compact to fit a lot of glucose in small spaces

• Branched structure increases surface area for rapid hydrolysis back to glucose

• Insoluble - won’t be affect water potential

Cellulose

Monomer - beta glucose

Bonds between the monomers - 1,4 glycosidic bonds

Function - structural strength for cell wall

Location - plant cells (cell wall)

Structure - polymer forms long, straight chains. Chains are held in parallel by many hydrogen bonds to form fibrils

How the structure leads to the function?

• Many hydrogen bonds provide collective strength

• Insoluble - won’t affect water potential

Glycogen

Monomer - alpha glucose

Bonds between the monomers - 1,4 1,6 glycosidic bonds

Function - stores glucose

Location - animal cell (muscle and liver cell)

Structure - a highly branched molecule

How the structure leads to the function?

• Branched structure increases area for rapid hydrolysis back to the glucose

• Insoluble - won’t affect water potential

triglycerides

formed via the condensation reaction between the one molecule of glycerol and three molecules of fatty acid, producing 3 water molecules and forming an ester bond

r group

it is a fatty acid which can be saturated or unsaturated and no of carbon and hydrogen can vary

saturated fatty acids

the hydrocarbons chain has only single bonds between carbons

unsaturated fatty acids

the hydrocarbons chain consists of at least one double bond between carbons

properties of triglycerides

1. energy storage. due to the large ratio of energy storing carbon hydrogen bonds compared to the number of carbon atoms, a lot of energy is stored in the molecule

2. due to the high ratio of hydrogen to oxygen atoms they act as a metabolic water source. triglycerides can release water if they are oxidised. this is essential of animals in the desert, such as camels.

3. triglycerides do not affect water potential and osmosis. this is because they are large and hydrophobic, making them insoluble in water

4. lipids have a relatively low mass. therefore a lot can be stored without increasing the mass and preventing movement

emulsion test

add ethanol to sample then distilled water then shake if the a white emulsion appears then lipids are present

phospholipids

made of glycerol molecule and two fatty acid chains and a phosphate group (attached to the glycerol)

the two fatty acids also bond to the glycerol via two condensation reactions resulting in two ester bonds

properties of phospholipids

hydrophilic ‘head’ of a phospholipid can attract with water as it is charged.

due to the phosphate being charged, it repels other fats

the fatty acid chain is not charged. it is known as the hydrophobic ‘tail’ and it repels water, but will mix with fats

have two charged regions, so they are polar.

In water they are positioned so that the heads are exposed to water and the tails are not

this forms a phospholipids bilayer membrane structure which makes up the plasma membrane around cells

what are proteins made up of

amino acids

central carbon with amine group on the left and a carboxyl group on the right and the R group on the top and Hydrogen on the bottom

What are the four structures in a protein

Primary structure

Secondary structure

Tertiary structure

Quaternary structure

Primary structure

The order of the amino acids in the polypeptide chains - this is a polymer

Secondary structure

the sequence of amino acids causes parts of a protein molecule to bend into alpha helix shapes or fold into beta pleated sheets.

• hydrogen bonds hold the secondary structure

tertiary structure

the further folding of the secondary structure. to form a uniqure 3D shape. held in place by ionic, hydrogen and disulphide bonds

quaternary structure

a protein made up of more than one polypeptide chainF

enzymes

tertiary structure protein which lowers activation energy of the reactions they catalyse. active site specific and unique in shape due to the specific folded and bonding in the tertiary structure of the protein; can only attach to substrates that are complementary in shape.

models of enzyme action

• induced fit, when the enzyme active site is induced or slightly changes shape, to mould around the substrate.

• E-S complex occurs, due to the enzyme moulding around the substrate it puts strain on the bonds and lowers the activation energy

factors affecting enzymes:

1. temperature

2. pH

3. substrate concentration

4. enzyme concentration

5. inhibitor

temperature affecting enzymes:

• temperature too low = not enough kinetic energy for successful collisions between the enzyme and substrate

• temperature too high = enzymes denature, the active site changes shape and enzyme - substrate complexes cannot form

pH affecting enzymes:

too high/low = interfere with the charges in the amino acids in the active site. can break the bonds holding the tertiary structure in place and therefore the active site changes shape

• therefore the enzyme denatures and fewer enzyme substrate complexes form

substrate and enzyme concentration affecting enzyme:

• insufficient substrate = reaction will be slower as there will be fewer collisions between the enzyme and substrate.

• insufficient enzymes = active site will become saturated with substrate and unable to work any faster

competition inhibitor

• same shape as the substrate

• bind to the active site

• prevents enzyme - substrate complexes

  • add more substrate it will flood/out - compete the inhibitior, knocking them out of the active site

non-competitive inhibitors

• bind to the allosteric site

• causes the active site to change shape

• no enzyme-substrate complexes

  • the substrate can no longer bind regardless of how much substrate is added.

test for starch

1. add iodine

2. a positive test observation = solutions turns from orange to dark blue/black

test for reducing sugars

1. add benedict’s reagent and heat

2. a positive test observation = solution turns from blue to green, yellow , orange or brick red (the more red the higher the concentration of reducing sugar)

test for non-reducing sugars

1. following a negative benedict’s test, where the reagent remains blue

2. add acid and boil - (this is acid hydrolysis)

3. cool the solution then add an alkali to neutralise

4. add benedict’s reagent and heat

5. a positive test observation = solutions turns from blue to orange or brick red (the more red the higher the concentration or reducing sugar)

test for proteins

1. add biuret

2. a positive test observation = solution turns from blue to purple

test for lipids

1. dissolve the sample in sample

2. then, add distilled water

3. a positive test observation = a white emulsion forms

DNA

codes for the sequence of amino acids in the primary structure of a protein, which in turn determines the final 3D structure and function of a protein

• therefore that cells contain a copy of this genetic code and that it can be passed on to new cells without being damaged

  • DNA polymer forms a double helix

DNA nucleotide

monomer that makes up DNA = nucleotide.

• deoxyribose ( a pentose sugar), a nitrogenous base and one phosphate group

  • guanine, cytosine, adenine and thymine

polynucleotides

• polymer of nucleotides = polynucleotides

• via condensation reactions between the deoxyribose sugar and the phosphate group, creating a phosphodiester bond

• DNA polymer occurs in pairs joined by hydrogen bonds between bases - creates the double helix

• hydrogen bonds can only form between complementary base pairs:

  • cytosine and guanine

  • adenine and thymine

RNA

polymer of a nucleotide formed a ribose, a nitrogenous base and a phosphate group

• bases: adenine, guanine, cytosine and uracil

relatively short polynucleotide chain and it is single stranded

function: RNA is transfer the genetic code from DNA in the nucleus to the ribosomes. some RNA (rRNA) is also combined with proteins to create ribosomes

DNA replication

• before cells divide all DNA must replicate to provide a copy for the new cell

• DNA replication = semi - conservative replication

semi - conservation replication

step1:

DNA helicase breaks the hydrogen bonds between the complementary base pairs between the two strands within a double helix. this causes the DNA double helix to unwind

step2:

each of the separated parental DNA strands act as a template. free floating DNA nucleotides within the nucleus are attached to their complementary base pairs on the template strands of the parental DNA

step3:

the adjacent nucleotides are joined together (to form the phosphodiester bond) by a condensation reaction. DNA polymerase catalyses the joining together of adjacent nucleotides

step 4:

the two sets of daughter DNA contains one strand of the prenatal DNA and one newly synthesised strand

evidence for semi-conservation replication

watson and crick discovered the structure of DNA in 1953 helped by Rosalind Franklin’s research on x-ray diffraction

meselson and stahl conducted an experiment which proves DNA replication must be semi - conservation

ATP

a nucleotide derivative, it is a immediate source of energy for biological processes. metabolic reactions in cells must have a constant, steady supply of ATP

• ATP made during respiration

• ATP can be hydrolysed using ATP hydrolase. releases a small amount of energy

can transfer energy to other compounds. inorganic phosphate released can be bonded onto different compounds to make them more reactive. known as phosphorylation.

five key properties of water

1. it is a metabolite

2. an important solvent in reactions

3. has a high heat capacity, it buffers temperature

4. high latent heat of vapourisation - providing a cooling effect with loss of water through evaporation

5. strong cohesion between water molecules; supports water columns and provides surface tension

inorganic ions

occur in solution in the cytoplasm and bodily fluids of organisms

• hydrogen ions ——> lower the pH of solutions and impact enzyme function and haemoglobin function. role in chemiosmosis

• iron ions ——> a component of haemoglobin in the transport of oxygen

• sodium ions ——> involved in the co transport of glucose and amino acids in absorption. in role in generating action potentials

• phosphate ions ——> a component of DNA and ATP