Biological Molecules

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define a monomer and give examples

• smaller units from which larger molecules are made from

  → amino acids/ monosaccharides/ nucleotides

define polymer

molecules made from a large number of monomers joined together

→ polysaccharides/ polynucleotide/ polypeptine

describe a condensation reaction

Involves the joining of two molecules (monomers) by a chemical bond

involves the elimination of a water molecule

a condensation reaction between two monosaccharides form a glycosidic bond

describe a hydrolysis reaction

hydrolysis reactions break the chemical bond (covalent) between two molecules

involves the use of water

define monosaccharaide and give examples

Monomers from which larger carbohydrates are made from

General formula (CH2O) n

→ glucose/ fructose/galactose

draw the alpha glucose and beta glucose molecules

glucose has two isomers:

define an isomer

molecules that have the same molecular formula but a different structural formula

how are the disaccharides formed

Condensation of two monosaccharides joined together by a glycosidic bond (C₁₂H₂₂O_{11 )}

glucose+ glucose → maltose + water

glucose +fructose →sucrose + water

glucose+ galactose→ lactose+ water

what are polysaccharides?

formed by the condensation of many glucose units

→ Starch/ Glycogen/ Cellulose

explain how the structure of starch leads to the function

made of alpha glucose monomers that form 2 polymers amylose-unbranched helix 1-4 glycosidic bondsamylopectin-branched molecule 1-4 and 1-6 glycosidic bond

• coiled/ helical can compact to fit many glucose

• branched structure increases SA for rapid hydrolysis back to glucose

  • glucose easily accessible by enzymes to break down for respiration

• insoluble so osmotically inactive

• Large so cannot cross cell-surface membrane

explain how the structure of cellulose leads to the function

• polymer forms long straight chains of beta glucose monomers that are only joined by 1-4 glycosidic bond

• chains are held in parallel by many hydrogen bonds to form a fibril structure

• many hydrogen bonds provide collective strength

• insoluble (wont affect water potential)

• can resist osmotic pressure

• bond is difficult to break

• resists actions of enzymes

describe the test for non-reducing sugars

1. do benedicts test + solution stays blue/negative

2. Add the sample in a test tube, add dilute HCL and boil for a few minutes to hydrolyse the glycosidic bond

3. Add sodium hydrogen carbonate powder to neutralise the solution

4. Add benedicts reagent, heat the mixture gently in a waterbath

how are triglycerides formed why aren’t they polymers

• Condensation reaction between one molecule of glycerol and three molecules of fatty acid forms ester bonds

• no repeating monomers

what’s the difference between saturated and unsaturated fatty acids

saturated-hydrocarbon chain has only single bonds

unsaturated-consists of at least one double bond between carbons

what are the properties of triglycerides

1. high ratio of carbon-hydrogen bonds→ releases more energy

2. low mass-energy ratio→ good storage molecule as doesn’t increase mass

3. large non-polar molecules→ insoluble in water+ waterproof

4. high ratio of hydrogen-oxygen bonds→ releases water when metabolised (source of water for dessert animals)

Compare and contrast the structure and properties of triglycerides and phospholipids

• Both contain ester bonds between glycerol and fatty acid

• Both contain glycerol

• Fatty acids o both may be saturated or unsaturated

• Both are insoluble in water

• Triglyceride has 3 fatty acids and phospholipids have 2

• Triglycerides are hydrophobic and phospholipids have hydrophilic and hydrophobic region

• Phospholipids form a monolayer in water but triglycerides don’t

describe the emulsion test

1. dissolve in alcohol(ethanol)

2. add distilled water and shake

3. white milky emulsion appears if lipid is present

How are phospholipids formed and describe the structure

• two fatty acids bond to glycerol molecule via two condensation reactions forming two ester bonds

• a phosphate molecule replaces the third fatty acid chain is covalently bonded to glycerol

• hydrophilic head-attracts water

• hydrophobic tail-repel water

  →forms the phospholipid bilayer structure

what are proteins and describe the amino acid structure

diverse group of large and complex molecules ,made from long chains of amino acids

How are polypeptides and dipeptides formed

• condensation reaction of many amino acids joined together by peptide bonds and this involves the formation of water

• Condensation of two amino acids Joined by a peptide bond

• H from the amine group

• OH-from carboxyl group

describe the biuret test

1. make the solution alkaline by adding a few drops of sodium hydroxide solution

2. add copper(II)sulphate→ copper bonds to peptide bonds

3. solution turns purple if protein is present

Give a description of each structural level of proteins

• primary: Sequence of amino acids and determines the ultimate shape and function

• secondary: Chain is twisted to form alpha helix or beta pleated sheets→ hydrogen in NH is slightly positive and oxygen in C=O is slightly negative so hydrogen bonds are formed

• Tertiary structure: further folding into 3D shape held by-hydrogen bonds/ionic bonds(carboxyl+ amine group) or disulfide bridges(sulfur in R group)

• Quaternary structure: made of two or more polypeptide chains

what is an enzyme

globular proteins which are biological catalysts to specific biological reactions

describe the induced fit model

The shape of the active site of an enzyme changes when the substrate binds to it

the enzyme becomes complementary

How does the active site of an enzyme cause a high rate of reaction

• In the Enzyme-Substrate complex there’s a change in shape of the active site

• Causes pressure to be placed on the bonds within substrate→ they begin to break

• reduces activation energy

describe the effect of substrate concentration on rate of reaction

• At low substrate conc= low rate of reaction, some active sites are free but limited chance of successful collision

• At intermediate substrate conc= high rate, more substrate molecules so high chance of successful collision

• High substrate conc= addition of more substrates has no effect as all active sites are saturated

describe the effect of enzyme concentration on RoR

• low enzyme conc- too few enzymes, not all substrates have active site so half possible RoR

• intermediate enzyme concentration- RoR increases as all active site full ,more substrate can occupy active site→ form products

• Addition of further enzymes have no effect on RoR as there are more enzyme than substrate

describe the effect of temperature on RoR

• increase in kinetic energy, more successful collisions

• past optimum-higher kinetic energy break bonds in tertiary structure

  →weaker hydrogen/ionic bonds

• shape of active site denatures, enzyme loses catalytic ability so no more ES complex

describe how PH effects RoR

• at optimum PH many collisions between enzymes and substrate→ high RoR

• change in PH means more or less ions in a solution, this affects the bonds in the tertiary structure

• active site becomes denatured, no successful collisions

how do competitive inhibitors lower ROR

• inhibitor has a similar shape to the substrate

• inhibitor is able to bind to active site

• fewer ES complexes formed

  → lower ROR

how do non-competitive inhibitors lower ROR

• inhibitor binds to a seperate site on the enzyme

• changing the shape of active site

• substrate can no longer bind so cannot form ES complex

how do inhibtors affect rate of reaction with increasing substrate concentration

• with competitive inhibitors the reaction reaches max rate but only at higher substrate concentration

• higher chance of collisions forming ES complex

• with non-competitive inhibitor reaction cannot reach max rate

How is DNA found in eukaryotic cells + prokaryotic cells

• packaged as chromosomes in the nucleus

• DNA associated with histones proteins→chromatins→chromosomes

• Most RNA in cytoplasm particularly ribosomes

Structure of DNA Nucleotide

• phosphate group

• Deoxyribose sugar, Pentose

• Nitrogenous bases: adenine, thymine, guanine, cytosine

• 3 components join together to form a mono nucleotide via condensation (using ATP)

Structure or RNA nucleotide

• phosphate group

• Ribose sugar

• Nitrogenous bases: Adenine, Uracil, guanine, cytosine

• Single stranded+ shorter than DNA

3 types of RNA

1. mRNA→ messenger, carries DNA code from nucleus to ribosome

2. tRNA→Transfer, carries amino acids across the cytoplasm

3. rRNA→ ribosomal, makes up the ribosome

How is the double helix structure of DNA formed

• the nucleotides join together via a condensation reaction between the phosphate group of one nucleotide and the sugar of another →phosphodiester bond

• Two DNA polynucleotide strands are joined by hydrogen bonds between the bases

• Two hydrogen bonds between A-T and three hydrogen bonds between C-G

Describe the process of semi-conservative replication

1. DNA Helicase breaks hydrogen bonds between bases

2. Each separated strand acts as a template

3. Free DNA nucleotides align by complementary base pairing

4. DNA polymerase joins adjacent DNA nucleotides in a condensation reaction using ATP forming phosphodiester bonds

5. Each new DNA strands are formed each with one original strand and one new strand

Chargaffs rules of base pairing

Number of guanine units= number of cytosine units

Number of adenine units= number of thymine units

How is DNA adapted for its function

• sugar-phosphate backbone→very stable

• Weak hydrogen bonding between bases→ can easily separate for DNA replication

• Many hydrogen bonding→ stable structure

• Extremely large molecule→ can store a lot of genetic information

• Double stranded→ strand can act as templates for semiconservative replication + allows accurate complementary base pairing

• Coiled→so can compact, good storage molecule

• Base sequence→ Allows for amino acid coding

Structure of ATP

• 3 phosphate molecules

• Pentose sugar molecule, ribose

• Adenine nitrogen containing compound

Equation for ATP Synthesis

ADP + Pi→ ATP + H20 catalysed by ATP synthase

H20 + ATP→ ADP+ Pi catalysed by ATP hydrolase

How is energy stored in ATP

• Bonds between phosphate groups are unstable

• Lower Ea

• Can easily be broken down

• Release a small amount of energy

Advantages of ATP

• releases energy in small manageable amounts

• Can be reformed again

• One single chemical reaction→ energy can be released quicker

• Can phosphorylate other molecules→ making them more reactive

• Does not move out of the cell

What are the properties of water

• metabolite→Allows metabolic reactions to occur

• Polar solvent→ allows metabolic processes to occur faster

• High SHC→ resists temperature changes

• High latent heat of vaporisation→ when evaporated it has a cooling effect

• Transparent→ allows photosynthesis of aquatic plants to occur

• Adhesive+ cohesive → allows water to be pulled up the xylem

Draw the interaction of water molecules

Describe the roles of iron ions, sodium ions and phosphate ions in cells

Iron: haemoglobin associates with oxygen

• Sodium:

• Co-transport of glucose/ amino acids into cells

• Na+ moves out by active transport

• Creates sodium concentration gradient

• Affects osmosis/ water potential

  Phosphate ions:

• Affects osmosis/ water potential

• Joins nucleotides in phosphodiester bonds

• Used in ATP

• Phosphorylates other compounds

• Hydrophilic part of phospholipid bilayer