2.2 Biological Molecules Flashcards
How do hydrogen bonds form between water molecules ?
Water is a polar molecule as oxygen and hydrogen have a sufficient difference in electronegativity
A slight charge forms on O and H, which allows intermolecular forces to form between molecules
State 7 biologically important properties of water
•Reaches maximum density at 4•C
•High surface tension
•Incompressible
•Solvent for chemical reactions
•High specific heat capacity
•High latent heat of vaporisation
•Cohesion between water molecules
Why is the incompressible property of water important for organisms ?
Provides turgidity for plants
Provides hydrostatic skeleton for some small organisms
Explain why ice floats on water and why this is important for organisms
Ice is less dense than water as Hydrogen bonds cause molecules to expand when becoming solid
This is important for life as it forms insulating ice caps at the poles and keeps the planets water at a suitable temperature
Why is the high surface tension of water important for organisms ?
It allows some organisms to live on the surface of water.
Why is water an important solvent for organisms ?
Allows the transport of molecules with a charge or dipole for inter and extra cellular purposes.
Why is the high specific heat capacity and latent heat of vaporisation of water important for organisms ?
SHC - Hydrogen bonding in water means that water temperature wont change drastically as kE will be used weakening H-bonds. This allows organisms to resist fluctuations in temperature
LH - High energy required to vaporise water. Allows organisms to sweat to lose heat energy from the body
Define monomer and polymer. Give examples of both
Monomers (such as monosaccharides, amino acids and nucleotides) are small repeating units which bond to form larger molecules
Polymers (such as polysaccharides, proteins and DNA) are formed when many monomers are bonded together
What happens in condensation and hydrolysis reactions ?
Condensation - a reaction which joins two biological monomers and gives H2O as a biproduct
Hydrolysis - a reaction in which a bond between two monomers is broken using water
Name the molecules found in carbohydrates, lipids, proteins and nucleic acids.
Carbohydrates/lipids : C, H, O
Proteins : C, H, O, N, S
Nucleic acids : C, H, O, N, P
Describe / draw the structure of α-glucose and β-glucose.
Both are hexose monosaccharides
Both have OH groups on all carbons but 5
Both have a methyl-OH group on C5
Both have an O between carbon 1 and 5, forming a ring
The only difference between the two molecules is that α-glucose has both hydroxyl groups on 1 and 4 pointing down and β-glucose has the C1 OH pointing up.
Describe the properties of α-glucose.
Small and easily soluble, allows for easy transportation in the blood
Complementary shape for antiport (swap) for co-transport for absorption in the gut
Complementary shape for enzymes for glycolysis
Describe / draw the structure of a ribose sugar.
A pentose monosaccharide with OH groups on all carbons except C4
A methyl-OH group is on C4
An oxygen is bonded between C1 and 4
What type of bond forms when monosaccharides react? What are the molecules called ?
The types of glycosidic bonds are α 1-4, α 1-6 and β 1-4
(α 1-2 exists only in sucrose)
Two monosaccharides bonded are a disaccharide, any more is a polysaccharide.
Name three disaccharides and describe their structure.
Maltose : glucose + glucose
Sucrose : glucose + fructose
Lactose : glucose + galactose
Describe the structure and functions of starch.
Starch is an energy store for plant cells made of α-glucose
It is insoluble so doesn’t affect Ψ and is large so doesn’t leave the cell
It is made from amylose and amylopectin
Amylose - 1-4 bonds in a helix shape. Compact with H bonds
Amylopectin - 1-4 and 1-6 in a branched shape. Many ends to hydrolyse and get glucose for ATP
Describe the structure and function of glycogen.
Main storage polymer in animal cells, but is also found in plant cells
It is insoluble so does not affect Ψ and does not diffuse out of cells
Highly branched which allows many ends to be hydrolysed to get glucose for ATP
Compact
Describe the structure and function of cellulose.
Made of entirely β-glucose 1-4 bonds
Glucose molecules alternate at 180 degrees to keep chains straight
Made of sheets of unbranched chains which form hydrogen bonds between layers
High strength provides turgidity
How do triglycerides form ?
3 fatty acid chains bind to a glycerol in a condensation reaction
Contrast saturated vs unsaturated fatty acids.
Saturated fatty acids contain only C single bonds whereas unsaturated fatty acids have C double bonds
Saturated fats have a higher melting point than unsaturated
Saturated are solid at room temperature, unsaturated are liquids
Saturated are found in animal fats, unsaturated are found in plant oils.
Relate the structure of triglycerides to their function.
They are a dense energy source
Triglycerides are non polar and so are hydrophobic. They don’t dissolve and affect water potential
Poor conductor of heat so can insulate the body in adipose tissues
Describe the structure and function of phospholipids.
They are amphipathic molecules as they have both hydrophobic tails and hydrophilic charged phosphate heads
The two components are connected by a glycerol molecule
They form the phospholipid bilayer in cell and organelle membranes
Are triglycerides and phospholipids polymers?
No they are macromolecules.
Describe the structure and function of cholesterol.
It is composed of four carbon rings with one -OH group and one hydrocarbon tail on opposing sides of the molecule
Cholesterol adds stability to membranes and is also the starting point for many hormones
Describe / draw the general structure of an amino acid.
NH2CHRCOOH
How do polypeptides form ?
Condensation reaction between two amino acids
The OH from the carboxyl group and bottom H from the amine group form water and a peptide bond
A peptide bond is -CONH-
Define the primary structure of a protein.
The sequence of, number of and type of amino acids in a polypeptide
Determined by the sequence of codons on mRNA
Define the secondary structure of a protein.
The shape that hydrogen bonds that form between H and O on C=O and N-H cause.
Describe the two types of secondary protein structure and how they form.
An α-helix occurs when all of the amino acids are facing the same way (ie with R group facing the same way) and is a spiral like shape. H bonds form between the opposing sides of the helix.
β-pleated sheets occur when the protein is folded so that the there is a parallel region. Hydrogen bonds form and hold this parallel sheet in place
Define the tertiary structure of a protein. State and describe the bonds present.
The 3D structure of a protein that is caused by further folding
Disulphide bonds : very strong bonds between two sulphur molecules
Ionic bonds : strong bonds formed between two charged R groups. Broken by pH changes
Hydrogen bonds : abundant and weak
Define the quaternary structure of a protein.
When a protein consists of more than one polypeptide
3D structure of the numerous polypeptides held together by the same bonds as tertiary structure
May involve the addition of a prosthetic group.
Define the structure and function of a globular protein.
Spherical and compact
Hydrophilic R groups face outwards and hydrophobic R groups face inwards, typically water soluble
Involved in metabolic processes e.g. enzymes and haemoglobin
Describe the structure of haemoglobin.
Globular protein with a prosthetic group
2 α chains, 2 β chains and 4 prosthetic haem groups
Water soluble, dissolves in plasma
Fe2+ bind to O2 in lungs
Tertiary structure changes upon oxygen binding allowing subsequent O2 molecules to bind easier (cooperative binding)
Describe the structure and function of fibrous proteins.
Long chains of polypeptides
Insoluble in water
Useful for structure i.e. collagen in skin
List the functions of collagen, elastin and keratin
Collagen : component of bones, cartilage and connective tissue
Elastin : provides elasticity to connective tissues, skin, arteries, lungs
Keratin : structural component of hair, teeth, nails and outer epithelial layer of skin
Describe how to test for proteins in a sample.
Biuret solution confirms presence of peptide bond
Add equal volume of NaOH as sample to solution
Add a few drops of dilute CuSO4 solution to sample
Positive colour change is blue to purple, negative is it remaining blue
Describe how to test for lipids in a sample.
Dissolve sample in ethanol
Add an equal volume of water and shake
Positive result : milky white emulsion, negative result is no change
Describe how to test for reducing sugars.
Add an equal volume of Benedict’s reagent to the sample
Heat in water bath at 100 C for 5 minutes
Positive result : solution changes from blue to orange with a brick red pptx.
Describe the Benedict’s test for non-reducing sugars.
If test for reducing sugars is negative, then:
Add 1cm of HCl to hydrolyse the sugar. Heat for 5 minutes in boiling water bath
After 5 mins add calcium carbonate to neutralise
Do Benedict’s test again
Describe the test for starch.
Add iodine solution
Positive result is solution changing from orange to blue/black.
