1. Biological Molecules Flashcards
Water is a ___ molecule
Polar/dipolar
Explain why water is a polar/dipolar molecule
- Pairs of electrons slightly more attracted to oxygen: more protons in its nucleus
- Oxygen has slightly negative charge, hydrogen has slightly positive charge
What type of bonds form between water molecules?
Hydrogen bonds
What property of water do hydrogen bonds cause?
Cohesion
Define hydrogen bonds
Weak forces of attraction between a slightly negative and slightly positive group
Water is a ___ for all polar molecules
Solvent
Why is it biologically important for molecules to be able to dissolve in water?
- Many molecules that are transported around living things are dissolved in water (e.g. in blood)
- All metabolic reactions in living things happen in solution
What will dissolve in water?
- All polar molecules (e.g. glucose)
- All ions
- All ionic molecules
What won’t dissolve in water (give an example)?
Fats (e.g. oils) because they are non-polar
Water has a ___ specific heat capacity
high
What does having a high specific heat capacity mean?
Water absorbs/loses a relatively large amount of energy before changing temperature
Because of its high specific capacity, water acts as a ___
buffer against sudden temperature fluctuations/changes
Biological importance of water having a high specific heat capacity
- Important for homeostasis - easier to regulate internal temperature because living organisms are mostly water (enzyme activity!)
- Important for organisms that live in water (aquatic environments have a more stable temp)
Water and latent heat of vaporisation
Water has a high latent heat of vaporisation
Latent heat of vaporisation is…
the amount of energy absorbed before something turns into vapour
Biological significance of water having a high latent heat of vaporisation
Can act as a coolant (eg sweat) with little loss of water through evaporation
Why does water have a high latent heat of vaporisation
Hydrogen bonds need to be broken - this requires energy
Why does water have a high specific heat capacity
Hydrogen bonds
Water will stick to other polar molecules - this is known as
Adhesion
Why is cohesion important in plants?
Water column doesn’t break up when water is pulled up the xylem in the transpiration stream - continuous
When does water show surface tension
At an air-water surface due to the cohesion between water molecules
What does surface tension do
Makes a solid-like surface, explaining why pond skaters can walk on water
Condensation reaction
Two monomers joining together to form a polymer and water
Hydrolysis reaction
A polymer splitting up into monomers - water required as a reactant
What do monosaccharides and disaccharides have in common?
They are sugars: sweet-tasting and very soluble
What general property do polysaccharides share?
Insoluble in water
How can monosaccharides form disaccharides and polysaccharides?
Through condensation reactions
Examples of monosaccharides
Glucose Fructose Galactose Deoxyribose Ribose
General formula of monosaccharides
(CH2O)subscript n
What is meant by a hexose sugar?
Has 6 carbons
Maltose =
glucose + glucose
Sucrose =
glucose + fructose
Lactose =
glucose + galactose
What type of bond forms between the two glucose molecules in maltose?
1-4 glycosidic bond
What type of glucose is used in maltose?
Alpha glucose
Are all monosaccharides reducing sugars?
Yes
Are all disaccharides reducing sugars?
No - only some are!
What is the test for reducing sugars?
Benedict’s solution
What do reducing sugars act as?
Reducing agents (they donate electrons)
The blue colour in Benedict’s solution is due to…
Cu2+ ions
They are soluble
The red colour in Benedict’s solution is due to…
Cu1+ ions
They are insoluble
Test for non-reducing sugars
- Negative Benedict’s result
- Hydrolyse sample to split into monosaccharides: add HCl, heat in water bath, neutralise with hydrogencarbonate
- OR add an enzyme
- Repeat Benedict’s test - if brick red there is non-reducing sugar
Benedict’s solution practical main point
The colour and density of any precipitate formed with Benedict’s solution can be used to indicate the concentration of reducing sugar present in a sample
What does a colorimeter measure
Percentage transmission (% of light that passes through the solution) and percentage absorbance (% of light that doesn’t get through)
Polymers of alpha glucose
Starch & glycogen
Polymers of beta glucose
Cellulose
Most glucose molecules join via…
1-4 glycosidic bonds, forming a helical chain
What’s good about a helical chain
It can coil so it’s more compact
How do polymers of glucose become branched?
1-6 glycosidic bonds
Describe starch (storage polysaccharide? structure?)
- Storage polysaccharide in plants
- Polymer wound into a tight coil
- Mix of branched (amylopectin) and unbranched (amylose) chains
Starch properties
- Large & insoluble - doesn’t affect water potential, doesn’t easily diffuse out of cells
- Helix - compact, lots of glucose can be stored in a small space
- Branched - many ends so can be broken down rapidly
Glycogen is…
A more highly branched polymer of alpha glucose
Advantages of a more highly branched molecule
More compact and can be broken down even more rapidly (animals are more likely to suddenly need a lot of energy)
Cellulose structure
- Long straight chains held close to each other by hydrogen bonds
- Strong & rigid overall structure
- Every other glucose molecule is flipped so no helix - only long straight chains
Where is cellulose found
Storage polysaccharide in plant cell walls
Groups of cellulose molecules form…
Microfibrils, which are then arranged in parallel groups which form cellulose fibres
What are cellulose fibres like?
Rigid and strong - giving cell walls their strength
What are lipids made of
Carbon, hydrogen and oxygen but proportionally less oxygen than carbs
Are lipids soluble in water?
No - they are non-polar and hydrophobic
What are lipids soluble in?
Organic solvents e.g. ethanol
Opposite of hydrophobic
Hydrophilic
Most important groups of lipids are…
Triglycerides - includes all fats and oils
Other types of fats include…
Cholesterol, phospholipids, waxes
Four different roles of lipids in living organisms
- Source of energy (often used as an energy store) - lipids have more energy per gram than carbs
- Insulation - poor conductor of heat
- Protection (around organs esp those outside the ribcage)
- Waterproofing - it’s hydrophobic!
What is a triglyceride molecule made up of?
3 fatty acids and 1 glycerol molecule
What does the “n” in fatty acid structural diagrams mean?
Number of repeats (of CH2 units)
What reaction forms a triglyceride?
Condensation
What bonds form in a triglyceride after condensation?
Ester bonds
What 3 properties make triglycerides a good energy storage molecule?
- Triglycerides have many energy-storing C-H bonds. This makes then an excellent source of energy.
- They are also very energy dense (lots of energy per gram) which makes them a good energy store.
- Being non polar also means they are insoluble - a useful property in a storage molecule.
Lipids vs. glycogen as energy stores
- Glucose can be used immediately in respiration - faster, short-term energy store. More readily available energy. Can be used in aerobic and anaerobic respiration.
- Lipids can only be used in aerobic respiration - energy is less readily available.
Difference between saturated & unsaturated fatty acid
Saturated has single bonds only & straight chain & tend to be solid @ room temp, unsaturated contains C=C double bonds (and wherever there is a double bond there’s a kink in the chain) & tend to be liquid @ room temp
Monounsaturated vs polyunsaturated
Monounsaturated: one C=C double bond
Polyunsaturated: many C=C double bonds
Why are unsaturated fats more likely to be liquid @ room temperature?
There are kinks in the chain so it’s harder to pack the fatty acid chains into a regular arrangement
Phospholipid structure vs triglyceride
A fatty acid has been replaced by a phosphate group (so two fatty acids, one glycerol, one phosphate group)
The head of a phospholipid molecule is…
hydrophilic
The tail of a phospholipid is…
hydrophobic
What do we call a molecule that is part hydrophilic and part hydrophobic?
Amphipathic
What happens when a phospholipid is in water?
Forms a micelle (see Notion for diagram)
Describe chemical test for lipids (emulsion test)
- Mix sample with ethanol - lipid is dissolved
- Add water - any previously dissolved lipid in ethanol will come out of solution, forming tiny lipid droplets
- The droplets give a white milky appearance
Proteins are made of _____ which are joined together by _____
Amino acids; Peptide bonds
Some proteins contain which element?
Sulphur
What elements are all proteins made of?
C, H, O, N
Examples of proteins
- Keratin & collagen: found in skin, hair, nails & connective tissue
- Actin & myosin: found in muscles
- Enzymes
- Haemoglobin
- SOME hormones (e.g. insulin)
- Antibodies are made of a protein called immunoglobin
Keratin and collagen are examples of…
Structural proteins
Is immunoglobin soluble or insoluble?
Soluble
Are enzymes soluble or insoluble?
Soluble
What are the three parts of an amino acid?
Amino group
R group
Carboxyl group
Is amino group acidic or basic?
Basic
Is carboxyl group acidic or basic?
Acidic
Define primary structure of a protein
The order of amino acids in the polypeptide chain (chain of amino acids)
Why is primary structure significant?
- It determines the final shape and properties of the molecule
- A mistake in the order can lead to a change in the molecule’s shape and properties, and therefore stop it carrying out its function
Define tertiary structure of a protein
The way in which the polypeptide is further twisted and folded to make a 3D shape
What bonds hold secondary structure of a protein in place?
Hydrogen bonds between the N-H (slightly positive) group on one amino acid and the C=O (slightly negative) group on another
Two types of secondary structure
Alpha helix
Beta pleated sheet
What bonds hold the tertiary structure in place?
Disulphide bridges, ionic bonds and hydrogen bonds between the R groups
What R groups/amino acids do disulphide bonds form between?
Ones with sulphur in them (i.e. cysteine R groups and methionine R groups)
Where are ionic bonds in a tertiary structure found?
They form between R groups that are charged
Where are hydrogen bonds in a tertiary structure found?
Weak bonds between R groups with a slight charge
What is quaternary structure?
When some proteins made up of several polypeptide chains, each with their own tertiary structure, join together to make one larger protein
Examples of proteins with quaternary structure
Haemoglobin - made of 4 polypeptides joined together
Some proteins with a quaternary structure might also have…
Prosthetic groups - non-protein parts of the molecule (e.g. in haemoglobin it’s Fe)
Biuret test for proteins
- Add NaOH
- Add 1% CuSO4 drop by drop
- Allow mixture to stand for 5 min: positive result is blue to violet
Role of phospholipids
What cell membranes are made of - forms barrier between cell interior & exterior
Globular vs fibrous proteins: what type?
Globular: usually metabolic (i.e involved in chemical reactions in the body)
Fibrous: structural
Globular vs fibrous proteins: solubility
Globular: soluble in water
Fibrous: insoluble in water
Globular vs fibrous proteins: primary structure
Globular: irregular & specific
Fibrous: repetitive sequences
Globular vs fibrous proteins: easy/hard to denature?
Globular: unstable so relatively easy to denature
Fibrous: stable so much harder to denature
Examples of globular proteins
Enzymes
Haemoglobin
Hormones
Examples of fibrous proteins
Keratin
Collagen
Actin
Myosin
