2.1.2: Biological molecules Flashcards
Catabolic reaction
Large molecule broken down to smaller molecules e.g. hydrolysis
⟶ Energy given out (to surroundings)
Anabolic reaction
Smaller molecules built up to large molecule e.g. condensation reaction
⟶ Energy taken in (required)
Features of a hydrolysis reaction
- “Splitting with water”
- Catabolic
- Covalent bond broken
Features of a condensation reaction
- Water molecule produced
- Anabolic
- New covalent bond formed
Hydrogen bonding occurs when…
- Slightly negatively charged part of molecule contacts & attracts slightly positively charged part of molecule.
- Between H and O.
Individual hydrogen bonds are ____
weak but due to large numbers their effect can be big.
Effect of H-bonding on polymers
Strengthens and stabilises polymers.
Properties of water
- High SHC
- High latent heat of vaporisation
- Cohesion
- Surface tension
- Polar so can form H-bonds
- Expands when freezes
- Can act as solvent
Water’s high SHC
• Due to H-bonding, water molecules stick to one another
• Hard to separate molecules
• Higher boiling point than expected
• High SHC
⟶ Acts as a buffer to sudden temp. changes, keeps an environment stable
Water’s high latent heat of vaporisation
• Due to H-bonding, water molecules stick to one another
• Lots of energy needed to evaporate 1 gram of water
⟶ Sweating = effective cooling mechanism in mammals
Cohesion in water
Cohesion: tendency of water molecules to stick to each other
⟶ Allows water to be pulled up tube (xylem)
Surface tension in water
Body of water moves as one mass
• Water molecules at the edge of a body of water are pulled back in rather than escaping
⟶ Allows pond skater to skate across pond
Water’s density when freezing
• Water becomes less dense when it freezes
⟶ Ice floats, insulating water beneath and allowing organisms to survive
Water as a solvent
• Polar, interacts with other polar molecules
• Interaction of +ve and -ve charges keeps solute molecules apart hence it dissolves
⟶ Molecules in solution can move/react with other molecules –> water = basis for metabolic reactions
Functions of carbohydrates
- Energy source
- Energy store
- Structure (cellulose in wall)
- Parts of larger molecules (nucleic acids)
Generalised formula of a monosaccharide
C𝒏(H₂O)𝒏
Types of simple sugars
- Triose
- Pentose
- Hexose
Prefix = no. of carbons
Arrangements of glucose
- Chain
* Ring
Forms of glucose ring
Alpha
Beta
Alpha glucose
H above OH on C1
Beta glucose
OH above H on C1
Glycogen contains _ glucose
𝛂
Cellulose contains _ glucose
β
Glycosidic bond
Covalent bond between two monosaccharides
Sucrose
Glucose + fructose
Lactose
Glucose + galactose
Maltose
Glucose + glucose (both 𝛂)
Elements that make up carbohydrates
C
H
O
Elements that make up lipids
C
H
O
Elements that make up proteins
C H O N S
Elements that make up nucleic acids
C H O N P
Example of a pentose monosaccharide
Ribose
Carbohydrate polymers are stores of
potential energy
Large polysaccharides are ______ so do not affect ______
Large poysaccharides are insoluble so do not affect osmosis
Where is the glycosidic bond in amylose
1,4 glycosidic bond
Amylose arranged in coil so
very compact
Glycogen arrangement
- Branched (v. compact)
* Can be hydrolysed quickly
Where are the glycosidic bonds in glycogen?
- 1,4 glycosidic bond
* 1,6 linkage (forms branches)
Why is glycogen good for storage?
- Insoluble
- Very compact
- Large enough = doesn’t diffuse out easily
- Branches at 1,4; linkage at 1,6 –> lots of potential enzyme attachment, hydrolysis sites
Why high conc. glycogen = good athletic performance
- Glucose stored as glycogen
- Glucose used for respiration to produce ATP
- ATP needed for muscle contraction etc.
Conjugated proteins contain…
a prosthetic group
Globular proteins
- spherical, water soluble proteins
- hydrophilic outside, hydrophobic core
- Have chemical functions in living organisms, e.g. enzymes, hormones
Fibrous proteins
- Long, insoluble structural proteins
- Lots of hydrophobic R groups
- Examples: keratin, elastin, collagen
Collagen
- 3 polypeptide chains twisted around each other
- 35% glycene
- Make up tendons, cartilage, artery walls
Elastin
- Many soluble tropoelastin molecules linked to form one stable, cross-linked structure
- Interactions between hydrophobic regions, crosslinks = covalent bonds –> gives strength and elasticity to skin, tissues
Primary structure
the sequence of amino acids in a protein
Basic chain
the order of the amino acids
Secondary structure
the initial folding of the primary structure
Secondary structure types
- Alpha helix
* Beta pleated sheet
Alpha helix structure
Hydrogen bonds form
between H-N….C=O
every 4 amino acids
Beta pleated sheet structure
Hydrogen bonds form
between H-N…C=O
but not at regular intervals
Tertiary structure
provides a protein’s 3D shape.
Hydrophobic interaction in a protein
interaction pushing apart parts of molcule
Ionic bonds in a protein
polar interactions between R groups, help maintain shape, stronger than H-bonds
Disulfide bridges
very strong covalent bonds, offer further suppport.
2 R groups with sulphur required
Cellulose structure
- Contains β glucose
- 1,4 glycosidic bond
- Alternate β glucose molecules rotated 180°
- Hydroxyl groups projected either side of chain –> allows H-bonding to occur between chains
Where do plant cell walls get their strength
- From cellulose microfibrils –> bundles of 60-70 cellulose molecules lie parallel
- H bonding between hydroxyl groups of neighbouring chains
Fat
lipid that is solid at RTP
Oil
lipid that is liquid at RTP
Lipis are __________ so _________
Lipids are non-polar so insoluble
Triglyceride
Contains glycerol and 3 fatty acids
Glycerol
3 carbon molecule with 3 OH groups
Saturated
all available bonds in the hydrocarbon chain have a hydrogen attached.
Unsaturated
not all available bonds in the hydrocarbon chain have a hydrogen attached
Where are saturated triglycerides found?
In animal products
Where are monounsaturated triglycerides found?
in cell membranes
Where are polyunsaturated triglycerides found?
in vegetable oil e.g. olive oil
How is a triglyceride formed?
- Condensation reaction repeated 3 times
- 3 water molecules produced
- 3 ester bonds formed
Why are triglycerides good energy stores?
- Insoluble: hydrophobic charges all around molecule, cannot H bond with water, does not affect ψ
- High calorific value: gives out 2x as much energy as the same mass of carbohydrates would
Differences between triglycerides and phospholipids
- Phospholipids contain a phosphate group
- Triglycerides contain 3 fatty acids, phospholipids contain 2
- Triglycerides are totally hydrophobic, phospholipids have a hydrophilic head and hydrophobic tail
How are lipids respired?
- Can be respired directly
- Hydrolysis of ester bond required
- Glycerol and fatty acids completely broken down into carbon dioxide and water
- Releases energy used to make ATP
Cholesterol
- Small, made from 4 carbon-based rings
- Narrow and hydrophobic
- Found in membranes, between tails of phospholipids
- Helps regulate strength and fluidity of membrane
Steroid hormones
- Made from cholesterol
* Lipid based, can pass through phospholipid bilayer into target cell
Cholesterol is needed for
Plasma membrane
Hormones
Cholesterol is made in
many cells especially those in the liver
In excess, cholesterol
can cause formation of gall stones, build up in arteries and lead to stroke, heart attack
Where is starch found?
In chlorolplasts and plant storage organs
What is starch made from?
2 polysaccharides:
• Amylose (20%)
• Amylopectin (80%)
Starch is soluble/insoluble?
Insoluble, so does not affect ψ.
Starch and glucose - shared features
✔︎ Energy storage molecules
✔︎ Insoluble –> do not affect ψ
✔︎ Long chains (of glucose); can be hydrolysed for respiration to produce ATP
Ca²⁺ uses
- Nerve impulse transmission
* Muscle contraction
Na⁺ uses
- Nerve impulse transmission
* Kidney function
K⁺ uses
- Nerve impulse transmission
* Stomatal opening
H⁺ uses
- Catalysis of reactions
* pH determination
NH₄⁺ uses
• Production of nitrate ions by bacteria
NO₃⁻ uses
• Nitrogen supply to plants, for amino acid and protein formation
HCO₃⁻ uses
Maintenance of blood pH
Cl⁻ uses
• Balance positive charge of sodium and potassium ions in cells
OH⁻ uses
- Catalysis of reactions
* pH determination
Benedict’s test method - reducing sugars
1) Add sample to test tube. If solid, grind up into water.
2) Add benedict’s reagent.
3) Heat mixture gently in water bath set to 80°C for 5 mins.
Benedict’s test method - non-reducing sugars
1) Add dilute hydrochloric acid to sample in test tube.
2) Heat for a few minutes to hydrolyse the glycosidic bond.
3) Add sodium hydrogencarbonate powder to neutralise the solution. The solution should fizz.
4) Add Benedict’s reagent.
5) Heat mixture gently in water bath set to 80°C for 5 minutes.
Benedict’s test results
✘ Blue ✔︎ Green - v. low ✔︎ Yellow - low ✔︎ Brown - medium ✔︎ Brick-red/orange - high
Emulsion test - method
1) Add ethanol to test sample
2) Shake thoroughly so that any lipids in the sample are dissolved
3) Add water and shake gently
Emulsion test - results
✘ Colourless and transparent
✔︎ Formation of cloudy white emulsion
Emulsion test - safety
- Ethanol is highly flammable
* Goggles should be worn when ethanol is handled
Iodine Iodide test - method
1) Add a few drops of Iodine Iodide solution to the test sample
Iodine Iodide test - results
✘ Yellow/brown
✔︎ Blue-black
Biuret test - method
1) Sample in solution in test tube
2) Add an equal volume of sodium hydroxide at RTP
3) Add a few drops of dilute copper sulphate and mix gently
Biuret test - results
✘ Blue (pale because dilute)
✔︎ Lilac/purple colouration
Food test for starch
Iodine Iodide test
Food test for proteins
Biuret test
Food test for simple sugars
Benedict’s test
Food test for lipids
Grease spot/emulsion
Name of process in which triglycerides are formed
Esterification
