molecules Flashcards
what is the importance of water as a solvent?
- The majority of the cell’s reactions take place
in aqueous solutions e.g cytoplasm. - Water’s solvent properties also mean
that it acts as a transport medium, as in
the blood plasma, urine, xylem and
phloem vessels. - Has different effects on hydrophilic (‘water
loving’) and hydrophobic (‘water hating’)
molecules. E.g lipids are hydrophobic (non-
polar) and do not dissolve in water - Has an important role in temperature
regulation since evaporation of water from
a surface cools it down
explain how water acts as a solvent
Water molecules are polar (charged) and so form
clusters around ions, glucose and amino acids
separating them in solution
what type of molecules will not dissolve in water?
non-polar molecules (hydrophobic) e.g lipids will
not dissolve in water
define the term buffer
chemicals
that resist changes in pH and ensure that a
particular environment maintains a particular
pH
give 2 examples of a buffer
- hydrogencarbonate ions
2.blood proteins e.g. albumin (the presence of dissolved
albumin stops too much water leaving the blood through
the capillaries by osmosis - regulates water potential).
explain the difference of the role of an acidic vs alkaline buffer
A buffer can act as both a base and an acid:
• Act as bases by mopping up hydrogen ions to help
neutralise an acidic solution.
• Act as acids by donating hydrogen ions to help
neutralise an alkali solution.
function of potassium
Is important in maintaining electrical gradients across neurones.
functions of calcium
- Calcium pectate is an essential component of the middle lamella of
plant cell walls. - Calcium is an essential component of bones and teeth in animals
- Calcium is essential in blood clotting and muscle contraction in
animals.
function of magnesium
. Essential in giving chlorophyll its light absorbing properties.
functions of iron
- Is part of the haem group in haemoglobin
- Important constituent of electron carriers in respiration.
function of nitrate
Is a component of amino acids, nucleic acids and chlorophyll.
functions of phosphate
- As phospholipids, phosphate is an important component of cell
membranes. - It is also a major component of other important biological molecules
including ATP and nucleic acids (DNA).
function of hydrogen carbonate
Important as a natural buffer
define macromolecules
large molecules e.g sucrose, maltose,
starch, cellulose, glycogen, proteins, triglycerides (lipid),
phospholipids and nucleic acids
define polymers
A large molecule formed of repeating similar
subunits (monomers) – joins by polymerisation
what 3 elements do carbohydrates contain
• Carbon
• Hydrogen
• Oxygen
general formula of carbohydrates
(CH2O)n.
what are monosaccharides
are the basic carbohydrate monomers i.e single (simple) sugars.
what are disaccharides?
are DOUBLE sugars formed form 2 monosaccharides monomers in a condensation reaction
what are polysaccharides?
are complex molecules usually containing of MANY monosaccharide monomers formed in condensation reactions
why is glucose an important monosaccharide
All green leaves make glucose using light energy (photosynthesis).
Our bodies transport glucose in the blood as all cells use it in respiration to release energy (produce ATP) – so are important ENERGY stores in living organisms (‘blood sugar’)
define the term isomer
the same molecular
formula but different structural formula
what is the difference between a- glucose and b- glucose
a- glucose is the basic subunit of complex polysaccharides such as starch and glycogen,
• b- glucose (different functional properties to a- glucose) is the constituent monomer of cellulose
describe formation of disaccharides
The chemical reaction when this happens is called a condensation reaction – one molecule of water is lost
This is a reversible reaction as a disaccharide molecule can be broken down into its constituent monosaccharide monomers in a hydrolysis reaction – one molecule of water is gained. (Hydrolysis reaction is important in the digestion of food)
what is the bond formed in condensation reaction of carbohydrates called?
glycosidic bond
what is general formula of disaccharides
All disaccharides have the general formula
C12H22O11.
name the important disaccharides and how they are formed
• Maltose – formed when two a- glucose molecules are linked through a condensation reaction
maltose is formed when starch is digested and requires further digestion to form monomer glucose
• Sucrose – formed when an a- glucose molecule condenses with a fructose molecule
sucrose is the form in which carbohydrates are transported in phloem of plants
• (Lactose – formed when an a- glucose molecule condenses with a galactose molecule)
why is starch such a good storage molecule?
• The molecules of both amylose and amylopectin are very COMPACT (aided by the coiled configuration) and, therefore, they contain a rich store of glucose in a small space.
• As it is INSOLUBLE, it will not affect the water relations of the cell – if significant quantities of carbohydrate were stored as glucose this would cause a lot of water to enter by osmosis.
• Being a LARGE MOLECULE it can be retained in the cell and will not easily pass through the cell membrane.
• The BRANCHING nature of amylopectin creates MANY TERMINAL ENDS that are EASILY HYDROLYSED. This aids in the rapid enzymatic breakdown of starch into its constituent glucose molecules at time of high respiratory demand.
the dlipping of 2 adjacent monomers have 2 effects, what are they?
- The unbranched chains are straighter, as the bulky –CH2OH side groups alternate between being above and below the chain.
- Hydrogen bonds can form cross-linkages between adjacent chains (due to the oxygen and the side groups being available on both sides of the chain following the inversion of alternate β- glucose molecules).
how is high tensile strength created in cellulose?
The cellulose chains (molecules) are grouped together in microfibrils, with each microfibril consisting of many cellulose molecules. Plant cell walls are formed of the cellulose microfibrils orientated into many planes in a lattice structure to further increase its tensile strength.
lipids contain what 3 elements?
carbon, hydrogen and oxygen
describe properties of lipids
• Lipids are macromolecules but are not
polymers.
• Lipids are insoluble in water, they are
hydrophobic molecules but are soluble in
organic solvents e.g. ethanol and ether.
why are triglycerides hydrophobic?
It is because of the long
hydrocarbon tails that triglycerides are
hydrophobic.
what are triglycerides made up of?
• are made up from 3 fatty acid molecules joined
to a glycerol molecule.
• are formed from 3 condensation reactions
between the fatty acids and the glycerol i.e.
*water is removed.
what are bonds formed by condensation reaction of lipids called?
ESTER BONDS
how can fatty acids vary?
- The length of the chain, and,
• 2. Whether there are any double
bonds present in the hydrocarbon
chain
what is the difference between fats and oils?
• Fats are solid (usually animal product) (saturated)
• Oils are liquid (usually plant product) (unsaturated)
Triglycerides are macromolecules but
are not polymers. Explain why they are
not polymers
A triglyceride is not composed of
repeating sub-units – it has three fatty
acids attached to a glycerol
what are the functions of lipids?
energy store, thermal insulation, protection, waterproofing (waxy cuticle) and buoyancy
what are phospholipids?
Phospholipids are similar to triglycerides
but one of the fatty acids molecules is
replaced by a phosphate group (PO4
3-).
what are micelles?
When phospholipids are mixed with water
they can form surface layers and
spherical structures called micelles
Distinguish between a triglyceride and
a phospholipid
A triglyceride consists of 3 fatty acids
bonded to a glycerol, while a
phospholipid consists of 2 fatty acids
and a phosphate bonded to a glycerol
i.e one fatty acid is replaced by a
phosphate
what elements do proteins contain?
C H O N S
what are functions of proteins?
as enzymes, carrier proteins, antibodies, structural proteins, hormones or contractile proteins
how is function of proteins determined?
The specific function of a protein depends upon its shape. In turn the shape of the protein is determined by the specific sequence of amino acids in the protein chain.
amino acids differ by R groups, what are their effects?
Some residues carry a charge and so may be involved in hydrogen bonding, some are hydrophobic
• Influence solubility
• may act as buffers
• Role with forming tertiary structure of proteins
• forming active sites (enzymes)
• interactions with hormones
• forming receptor site
what are prions
Prions are a particular type of protein found in
mammals and some other animal groups.
what is the difference between normal vs disease causing prion?
• The secondary structure of normal protein PrP
is composed mainly of a- helixes
• The disease causing form (PrPSc ) has a
higher proportion of beta-sheets (compared to
a helixes)
properties of prions
Prions are stable, being resistant to extreme temperature and
radiation .
3 prion diseases
Scrapie that affects sheep
Bovine spongiform encephalopathy (BSE) or’mad
cow disease’ normally cattle are affected through
eating contaminated food products
Variant Creutzfeldt-Jakob disease (vCJD), a human
version of BSE that is normally acquired though eating
contaminated beef products containing the PrPSc
form. Humans lose memory and physical coordination.
how can prions arrise
spontaneously, by mutations or by eating contaminated food
primary structure of proteins
The primary structure of a polypeptide(protein) is the sequence of amino acids joined together by peptide bonds in the polypeptide chain.
secondary structure a-helix
Themostcommonshapesare formed either by coiling to form an a-helix
Hydrogen bonds formed between amino acids at regular intervals)
Thebondstwistthechainof amino acids into a spiral or helical shape.
Secondary Structure b - pleated-sheets
• Another secondary structure is the folding into b - pleated- sheets
• These are more rigid and less flexible than a-helix
• They are formed by sections of the polypeptide chain
oriented in opposite directions, lying adjacent to each other
• Hydrogen bonds form between the C=O and NH groups
tertiary structure
This additional folding gives each protein its unique 3D shape and is a consequence of the range of bonds formed between the R-groups of amino acids in the chain.
quaternary structure
The quaternary structure of a protein arises when two or more polypeptides are bonded together (largely by disulphide bonds), forming a complex, biologically active molecule.
conjugated proteins
Have a non protein part attached .
• The non protein component is called the
prosthetic group.
• These conjugated proteins include glycoprotein which is important in the cell membrane
fibrous protein
consistofpolypeptidesarrangedinparallel chains, linked together to form long fibres
- Theparallelchainsarelinkedbycross-bridges to form very strong and stable molecules.
- Theyhaveastructuralfunction
Examples of fibrous proteins are:-
• fibrin - This is a blood protein involved in blood clotting.
• collagen-acomponentofbloodandtendons.
• keratin-foundinhair,hornandnails. .
• E.g. Collagen - a single collagen fibre
globular proteins
• Otherproteinstakeupatertiarystructurethatis more spherical. These are called globular proteins.
• Theirveryspecific3Dshapeiscrucialtotheir metabolic role
• Mostenzymes,haemoglobinantibodiesand some hormones are globular proteins.
Describe the similarities and differences between haemoglobin and collagen
Similarities–both are quaternary structures and are found in animals
• Differences–haemoglobin 4 polypeptides, collagen has 3
• 2 types of polypeptide occur in haemoglobin while collagen they are identical
• haemoglobinisglobular,collagenisfibrous
what are sub units of nucleic acids
The sub unit of nucleic acids is the nucleotide
• Each nucleotide consists of three components
• Pentose sugar (5 carbon) (deoxyribose - DNA, ribose- RNA)
• Phosphate group
• nitrogenous base (always contains nitrogen)
how are components combined in nucleotide?
•The three components are combined as a consequence of condensation reactions to form the nucleotide.
•Phosphodiester bonds link pentose sugar molecules to phosphate in a nucleic acid strand.
what are two types of nucleic acid
DNA
RNA
describe a molecule of DNA
•A molecule of DNA consists of 2 anti-parallel strands with the two strands being held together by hydrogen bonds between adjacent bases
what does anti parallel mean
Anti-parallel means the two strands a running in opposite directions
what is the base pairing rule?
•Adenine only pairs with thymine (by 2 hydrogen bonds)
•Guanine only pairs with cytosine (by 3 hydrogen bonds)
how is dna arranged?
•The DNA molecule is organised as a double helix
•Each strand of the DNA is wound round each other like a twisted ladder, linked together by the bases, following base pairing rules.
•The organization of the DNA is very regular, with there being 10 base pairs for each complete turn of the helix
explain semi conservative replication
- 2.
- 4.
TheenzymeDNAhelicase‘unzips’thetwostrandsoftheDNAbybreakingthe HYDROGEN BONDS between the bases. This allows EACH of the ORIGINAL STRANDS to become a TEMPLATE for the formation of TWO DNA molecules.
FREE NUCLEOTIDES are linked to the template strands in the correct sequence as a consequence of bases on the ‘free’ nucleotides following BASE PAIRING RULES with the bases on the template strands.
The nucleotides of each strand are joined together by the enzyme DNA POLYMERASE
Each of the new DNA molecules contains one original (template) strand and one new DNA strand. This is why the process of DNA replication described is called SEMI- CONSERVATIVE REPLICATION.
what is evidence for semi conservative replication
- THE CONSERVATIVE MODEL – this proposed that the parental DNA remained intact but copied the new DNA molecule (analogous to a photocopier).
- THE SEMI-CONSERVATIVE – as described at earlier and in the previous diagram.
One of the most famous experiments in the history of Biology was carried out by Meselson and Stahl, who proved that the SEMI-CONSERVATIVE model is the process involved.
Meselson and Stahl cultured the bacterium E.Coli using the ‘heavy’ isotope of Nitrogen, 15N. The 15N was incorporated into the bases of the DNA in all the bacteria over time, as older bacteria (containing the normal 14N) died and were replaced.
The bacteria were then transferred to a medium containing the lighter (normal) 14N.
what were the key stages of Meselson and Stahls experiments
- Bacteria growing in 14N (before transfer to 15N).
- Bacteria growing in 15N (many generations after transfer from 14N)
- One generation after transfer to 14N 4. Two generations after transfer to 14N.
Explanation of Meselson and Stahl’s results
• After one generation – The intermediate position of the DNA can be explained by ALL the DNA consisting of ONE STRAND that has the bases containing 15N and ONE STRAND having bases containing 14N.
• After two generations- About half the DNA consisted of ‘mixed’ DNA of both 14N and 15N but the other half was DNA that only contained 14N.
