Biology 3.1 Biological Molecules

AQA A Level Biology Biological Molecules

All organisms share a common chemistry; there are the same groups of carbon-based compounds in cells.

What provides indirect evidence for evolution?

Small units from which large molecules are made.

Define monomer.

Molecules made from a large number of monomers joined together.

Define polymer.

Hydrogen is above Carbon 5.

Structure of alpha-glucose.

Hydrogen is below Carbon 5.

Structure of beta-glucose.

Glucose, fructose and galactose

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C6H12O6

Name the three hexose sugars and there molecular formula

Glycosidic

What bond forms when monosaccharides react

C12H22O11

What is the chemical formula for Maltose, Sucrose and Lactose

Equal vols benidict’s solution + sample

heat in a water bath

\+ = Blue → Orange/brick red ppt

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Semi quantitative as darker colour = stronger sugar

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What is the benidict’s test for reducing sugars

Hydrolase non-reducing sugars e.g. sucrose into monomers by adding 1cm3 HCl and heat

Neutralise using sodium carbonate until turns litmus paper green

Add benidict’s + = Blue → Orange/brick red ppt

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Describe the test for non reducing sugars

iodine + = orange → blue/black

Describe the test for starch

make standard solutions with known concs and record absorbance

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plot calib curve

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record absorbance for unknown samples use calib curve to read concs

Outline how colourimetry could be used to give qualitative results for the presence of sugars and starch’s

\- energy reserve for plants

\- polysaccharide made up of alpha-glucose

\- unbranched, coiled amylose – therefore it’s compact and good for storage

\- branched amylopectin – therefore enzymes can hydrolyse bonds easily and release energy quickly

\- insoluble + doesn’t affect water potential, therefore good for storage

Structure and function of starch.

\-energy reserve for animals

\- polysaccharide made up of alpha-glucose

\- branched with a lot of side branches – therefore enzymes can hydrolyse bonds easily and release energy quickly

\- compact therefore good for storage

Structure and function of glycogen.

Glucose + Glucose

How is maltose made

Glucose + Fructose

How is sucrose made

Glucose + Galactose

How is Lactose made

\- polysaccharide made up of beta-glucose

\- forms long, unbranched, straight cellulose chains

\- chains are linked with hydrogen bonds to form strong microfibrils

\- provides structural support for cells

Structure and function of cellulose.

The hydrocarbon tail which can be saturated or unsaturated.

What is the R group of a fatty acid?

\-energy storage molecule – the long hydrocarbon tails release a lot of energy when broken down

\- insoluble + doesn’t affect water potential – the hydrophobic tails face inwards and the hydrophilic heads face outwards, forming droplets

\- Slow conductor of heat, good insulator

Properties of triglycerides.

Glycerol + 3 fatty acids to form an ester bond

How are triglycerides formed?

\- makes up the bilayer of cell membranes

\- hydrophilic heads face outwards, hydrophobic tails face inwards, waterproofing

\- the centre is hydrophobic so water-soluble substances can’t pass through

Properties of phospholipids.

Ester bond

What bonds are found in triglycerides?

Dissolve the solid sample in ethanol add equal vol water and shake

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\+= Milky white emulsion

How do you test for lipids?

Sat: Only single bonds Unsat: C=C bonds

Sat: Straight chains, many contact points Unsat: Kinked chains, min contact

Sat: high mp, solid at room tempt Unsat: liquid at room tempt

Sat: found in animals Unsat: Found in plants

How do saturated and unsaturated fatty acids differ to one another?

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Glyercol backbone

Mix of sat and unsat fatty acids

Contain C,H and O only

Formed via a condensation reaction

How are phospholipids and triglycerides similar

Phos: 2 fatty acids 1 phosphate Trig: 3 fatty acids

Phos: Hydrophillic head + hydrophobic tail Trig: whole molecule is hydrophobic

Phos: Used mainly as membrane Trig: Used mainly as energy storage

How are triglycerides and phospholipids different?

NO, do not have repeating units

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They are macromolecules

Are phospholipid and triglycerides polymers?

They have different variable side groups (R groups).

20 different aminos

How do amino acids differ from one another?

NH2 amine group

COOH carboxyl group

R side chain

What is the general structure of an amino acid?

Biurets Test

Equal vol sodium hydroxide to sample

small amount of dilute copper (II) sulphate

mix

\+= blue → Purple

How do you test for proteins

A dipeptide joined by a peptide bond (CNOH)

more than two is a polypeptide

What does a condensation reaction between two amino acids form?

Sequence of amino acids

determined by codons in mRNA

What is the primary structure of a protein?

H bonding and then either Alpha helix or Beta pleated sheets

What is the secondary structure of a protein?

3D shape determined by folding

disulfate bridges

ionic bonding

H bonds

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Can be impacted by 1st structure due to amino sequence determining where bonds can occur

What is the tertiary structure of a protein

May contain may polypeptides

May have a prosthetic such as a metal

What is quaternary protein structure

\- substrate binds to the active site to form an enzyme-substrate complex

\- lowers activation energy of reaction by putting strain on the bonds in a molecule or reducing repulsion between two molecules

How do enzymes catalyse a reaction?

spherical/compact

Hydrophilic R group that faces outwards Hydrophobic faces inwards usually water soluble

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involves in metabolic process e.g. enzymes/haemoglobin

what is the structure/function of a globular protein?

Can form long chains/fibbers

insoluble

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good structure/support e.g. collagen in skin

Structure/function of fibrous proteins

Use a capillary tube to put mixture onto pencil line of origin and place paper in solvent

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allow solvent to run until it almost reaches the other end of the paper

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Use UV to see the spots

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Each amino will have a different Rf value

How can chromatography be used to identify an amino acid?

\- the enzyme’s active site and the substrate are exactly complementary to each other

\- they bond to form an enzyme-substrate complex

Describe the ‘lock and key’ model.

\- the active site and substrate are specific to each other but not exactly complementary

\- they bind to form an enzyme-substrate complex, the active site changing shape slightly to complete the fit

Describe the ‘induced fit’ model.

\- the active site is determined by the tertiary structure

\- changes in pH and temperature affect the bonds in the tertiary structure, so active site changes shape so it’s no longer complementary to its substrate

How is the tertiary structure related to an enzyme’s active site?

Enzyme conc

Substrate conc

Inhibitors conc

pH

Tempt

5 factors that effect enzyme ROR

If enzyme conc is fixed rate increases in propotion to substate conc

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Rate levels off when max no, of E-S are formed

How do substrate conc effect enzyme ROR

Rate increases as Ke increases and peaks at optimum tempt

above optimum ionic and H bonds in 3rd structure of protein break

active site changes shape, no longer complimentary (denatured)

How does tempt effect enzyme ROR

Comp: Similar shape to substrate, binds to active site Non-comp: Bind to allosteric site

Comp: do not stop reactions ES complex can reform when inhibitor is released Non-Comp: can change active site shape and permanently stop reaction

Comp: increasing substate complex can decrease effect Non-comp: increasing con has no impact

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Contrast the two type of enzyme inhibitors

pH = -log10\[H+\]

How do you calculate pH

Outside optimum H+/OH- interact with H bonds in 3rs structure

How does pH effect enzyme ROR

a grpah showing ROR against time

draew a tangent where time = 0

How can results from a practical measuring enzyme activity be used to find the initial rate of reaction?

immerse equal vols of trypsin and milk stored in different test tubes in a water for 5 mins

mix together and time how long until the milk is hydrolysed (becomes a colourless solution)

test a differnt tempts

How can you practically measure the effect of temperature on enzyme activity using trypsin and milk?

1/time

How do you calculate ROR

(Uncertainty/measured value) x100

How do you calculate uncertainty

Holds genetic information.

What is the role of DNA?

Transfers genetic information from DNA to ribosomes.

What is the role of RNA?

RNA and proteins.

Components of ribosomes.

Deoxyribose sugar, phosphate group, and an organic base (adenine, thymine, cytosine or guanine).

Components of a DNA nucleotide.

Ribose sugar, phosphate group, and an organic base (adenine, uracil, cytosine or guanine).

Components of an RNA nucleotide.

Double helix with two polynucleotide chains held together by hydrogen bonds between specific complementary base pairs.

Describe a DNA molecule.

Phosphodiester

What bonding occurs between nucleotides?

Double helix with two polynucleotides chains held together via H bonds to specific bases

Describe a DNA molecule

DNA helicase breaks the H bonds between base pairs

Each strand acts as a template

free nucleotides from nucellar sap attach to exposed bases due to base pairing

DNA polymerase catalyses a condensation reaction that joins adjacent strands

H bonds reform

How does semiconservative replication happen?

Bacteria grown in medium containing heavy isotope N15 for many generations

some bacteria were moved toa medium containing light isotope N14 and extracted after 2 DNA replication cycles

Bacteria centrifuged formed a pellet heavy DNA settled at the bottom

Describe the Meselson and Stahl experiment

How does the Meselson Stahl experiment validate semiconservative replication

Ensures genetic continuity.

Why is semi-conservative replication of DNA important?

mRNA; Comp to 1 gene from DNA with introns spliced out, codons can be translated into polypeptides by ribosomes

rRNA: component of ribosomes

tRNA: Supplies complimentary aminos to codons during translation

What is the role of different types of RNA in living cells

A + G = 2 rings, purines

T/U + C 1 ring, pyrimidines

Which bases are purine and which are pyrimidines

A +T, 2 H bonds

G + C, 3 H bonds

What are the complimentary base pairs in DNA

\- hydrogen bonds between the bases are broken by DNA helicase, unwinding the double helix

\- the two strands act as templates

\- free DNA nucleotides are attracted to the exposed bases by complementary base pairing

\- DNA polymerase joins up the adjacent nucleotides, forming a sugar-phosphate backbone

Describe the process of semi-conservative replication.

Ribose sugar, three phosphate groups and an adenine base.

Components of ATP.

Sugar phosphate backbone/H bonds, stability

Long molecule, lots of info

Helix can compact for storage in nucleus

Base sequence of triplets codes for aminos

double stranded for semi-conservative replication

weak h bonds to easily separate for replication

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How does DNA structure relate to its function

Long nucleotide, still shorter than DNA, breaks down quickly

contains uracil instead of thymine

single stranded and linear with no base pairing

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RNA structure/function

single stranded

clover shape

anticodon on one end amino binding on other

anticodon binds to comp mRNA codon

amino acid corresponds to anticoding

RNA structure

Condensation reaction between ADP and Pi, catalysed by ATP synthase during photosynthesis or respiration.

Describe ATP synthesis.

ATP (Catalysed by ATP hydrolase) → ADP + Pi

Energy released coupled with metabolic reactions

phosphate group (Pi) phosphorylates compounds to make them more reactive

What’s the role of ATP in cells

high energy bonds between phosphate groups

small amount of energy released at a time to prevent wastes

single step hydrolysis

easily resynthesized

Why is ATP suitable as the energy currency of cells

Chemically simple, few components

Why was it doubted that DNA carried the genetic code

DNA, double stranded RNA, single

DNA, deoxyribose RNA, ribose

DNA, Thymine RNA, Uracil

DNA, Longer RNA, Shorter

Compare DNA to RNA

\- each molecule is made up of an oxygen atom covalently bonded to two hydrogen atoms

\- each molecule is polar due to the electronegativity of oxygen

\- there is hydrogen bonding between molecules

Structure of water.

\- metabolite

\- solvent

\- cohesion

\- high specific heat capacity – buffers changes in temperature

\- high latent heat of vaporisation – provides cooling effect with little loss of water

5 Properties of water.

\- found in cytoplasm and body fluids

\- H+ - determines pH

\- Fe2+ - binds to oxygen in haemoglobin

\- Na+ - used in co-transport of glucose and amino acids

\- PO43- - components of DNA, RNA and ATP

Location and roles of inorganic ions.