biological molecules- chapter 1 Flashcards
what is covalent bonding
atoms share a pair of electrons in their outer shells, as a result the outer shell of both atoms is filled and a more stable compound (molecule) is formed
what is ionic bonding
ions with opposite charges attract one another, this electrostatic attraction is known as an ionic bond
what is what is hydrogen bonding
the electrons within a molecule are not evenly distributed but tend to spend more time at one position, this region is more negatively charged than the other.
the negative region of one polarised molecule and the positively charged region of another attract each other, a weak electrostatic attraction is formed, they collective form important forces that alter the physical properties of the molecules
what is a polar molecule
an uneven distribution of charge is said to be polarised
what is a polymer
long chain on monomer sub units
how are polymers formed
polymerisation
what are monomers
individual molecules
what are 3 example of polymers
polysaccharides, polypeptides, polynucleotides
what are condensation reactions
reactions that produce water
two examples of condensation reactions
amino acid to polypeptide
monosaccharide to polysaccharide
what is hydrolysis
addition of water, water molecules are used when breaking the bonds that link the sub units
what can starch be hydrolysed into
glucose
what is metabolism
all chemical processes that take place in living organisms
what is a molar solution
a solution that contains one mole of solute in each litre solution
what do carbon atoms do
readily form bonds with other carbon atoms which make sequences of varying lengths
what are carbon-containing molecules known as
organic molecules
what do carbon molecules form
a ‘backbone’ along which other atoms can be attached
what is a disaccharide
a pair of monosaccharides combined together
what are polysaccharides
monosaccharides that can be combined in a much larger form
what is the general formula of a monosaccharide
(CH2O)n
describe a monosaccharide
sweet tasting soluble substance
in a monosaccharides formula what number can n be
any from 3 to 7
give 3 examples of monosaccharides
glucose, galactose and fructose
what are the two isomers of glucose
alpha-glucose and beta-glucose
what type of sugar is glucose and the formula
hexose sugar, general formula C6H12O6
example of reducing sugars
monosaccharides and some disaccharides
what is reduction
a chemical reaction involving the gain of electrons or hydrogen
what is a reducing sugar
a sugar that can donate electrons (or reduce) another chemical, benedicts reagent
what is benedicts reagent and what happens when its heated with a reducing sugar
alkaline solution of copper (II) sulfate
when a reducing sugar is heated with benedicts it forms as insoluble red precipitate of copper (I) sulfate
how do you carry out a reducing sugars test
- add 2cm3 of food sample to be tested to a test tube. if the same isn’t in liquid form, first grind it in water
- add an equal volume of benedicts reagent
- heat the mixture in gently boiling water bath for five minutes
glucose+glucose=?
maltose
glucose+fructose=?
sucrose
glucose+galactose=?
lactose
what bond is formed in condensation reaction
glycosidic bond
what is it good that polysaccharides are insoluble
makes them suitable for storage
what is cellulose good
not used for storage but gives structural support to plant cells
how is starch found
found in many parts of the plants in the form of small granules or grains
how is starch formed
joining of between 200 and 100000 a-glucose molecules by glycosidic bonds in a condensation reaction
how do you carry out the non-reducing sugars test
- add 2cm3 of food sample to 2cm3 of hydrochloric acid and place in a water bath. this hydrolyses the disaccharides present
- add sodium hydrogencarbonate to neutralise the acid, and check with pH paper
- test with 2cm3 of benedicts reagent, place in a water bath for 5 minutes. any change in colour is a positive result
what is the test for starch
add iodine solution to food sample
blue-black if there’s starch present
what type of chains are in starch
branched or unbranched
what does it mean in starch is the chains are unbranched
they’re wound into a tight coil that makes the molecules very compact
why is it good that starch is insoluble
doesn’t affect water potential, so water isn’t drawn into the cells by osmosis
why is it good that starch is insoluble
cannot diffuse out of cells
why is it good that starch is compact
a lot can be stored in a small space
what is release when starch is hydrolysed and why is this good
a-glucose
good because it is easily transported and ready for use in respiration
why is starch good branched
has many ends, each can be acted on by enzymes simultaneously meaning that glucose monomers are released very rapidly
where is glycogen found
in animals and bacteria cells but never plant
what is glycogens structure
similar to starch but has shorter chains and is more highly branched
where is glycogen stored
as small granules mainly in muscles and liver
why is it good that glycogen is insoluble
so it doesn’t draw water into the cells by osmosis and cannot leave by diffusion
why is it good that glycogen is compact
so a lot can be stored in a small space
why is it good that glycogen is more highly branched than starch
so has more enzymes to act on simultaneously, it is more readily broken down to be used in respiration
what is cellulose made of
b-glucose monomers
what are the chains like in cellulose
straight unbranched chains which run parallel to each other allowing hydrogen bonds to form cross-linkages between chains
why is cellulose strong
a lot of hydrogen bonds
why is it good that cellulose molecules are grouped together
forms microfibrils which are arranged in parallel groups called fibers- which provide more strength
how does cellulose stop a plant cell from bursting
exerts an inward pressure that stops any influx of water
how to plant cells become semi rigid
plant cells are turgid and push against one another, making non-woody parts semi rigid
why is it important for plant cells to be semi rigid
important in maintaining stems and leaves in a turgid state so that they can provide the maximum surface area for photosynthesis
what do lipids contain
carbon, hydrogen and oxygen
are lipids soluble or insoluble
insoluble in water
soluble in organic solvents such as alcohol and acetone
what are the main groups of lipids
triglycerides (fats and oilds) and phospholipids
what is the role of lipids is cell membranes
phospholipids contribute to the flexibility of membranes and the transfer of lipid-soluble substances across them
what is the role of lipids as a source of energy
when oxidised, lipids provide more than twice the energy as the same mass of carbohydrates and release water
why are lipids good for waterproofing
are insoluble in water
both plants and insects have waxy lipid cuticles while mammals produce an oily secretion from the sebaceous glands in the skin
why are lipids good for insulation
fats are slow conductors of heat and when stored beneath the body surface help to retain body heat
they also act as electrical insulators in the myelin sheath around nerve cells.
why are lipids good for protection
fat is often stored around delicate organs
what is a triglyceride
has 3 fatty acids and a glycerol combined
what bond does each fatty acid form with the glycerol
ester bond in a condensation reaction
what does saturated mean
no carbon-carbon double bonds, all the carbon atoms are linked to the maximum possible hydrogen atoms
what does mono unsaturated mean
single double bond
what does polyunsaturated mean
more than one double bond
why is it good that triglycerides have a high ratio of energy-storing carbon
hydrogen bonds to carbon atoms so is an excellent source of energy
why is it good that triglycerides have a low mass to energy ratio
makes them good storage molecules
why is it good that triglycerides are large, non polar molecules
insoluble in water, means their storage does not affect osmosis in cells
why is it good that triglycerides have a high ratio of hydrogen to oxygen atoms
they release water when oxidised and therefore provide an important source of water
what is a phospholipid
one fatty acid molecule is replaced by a phosphate molecule
what do fatty acid molecules do
repel water (hydrophobic)
what do phosphate molecules do
attract water (hydrophilic)
what two parts make up a phospholipid
hydrophilic head and hydrophobic tail
what does the hydrophilic head do
interact with water but not with fat
what does a hydrophobic tail do
orientates itself away from water but readily mixes with fat
why is a phospholipid said to be polar
as it has two ends that behave differently
why is it good that phospholipids are polar
means that in an aqueous environment, phospholipid molecules for a bilayer within cell-surface membrane
this forms a hydrophobic barrier is formed between the inside and outside of a cell
why is it good that phospholipids have hydrophilic phosphate ‘heads’
help to hold at the surface of a cell-surface membrane
why is the structure of phospholipids good
allows them to form glycolipids by combining with carbohydrates within the cell-surface membrane
glycolipids are important in cell recognition
what is the test for lipids
- take a completely dry and grease free test-tube
- add 2cm3 of sample to 5cm3 of ethanol
- shake the tube thoroughly to dissolve any lipid in the sample
- add 5cm3 of water and shake gently
- cloudy-white colour is a positive result
why is the positive result cloudy
due to any lipid in the sample being finely dispersed in the water to form an emulsion light passing through is refracted as it passes from oil droplets to water droplets making it appear cloudy
what is the structure of an amino acid
basic monomer unit that combines to make a polypeptide which are then combined to form proteins
what are the 4 different chemical groups atatched to an amino acid
amino group (-NH4)
carboxyl group (-COOH)
hydrogen atom (-H)
R group- a variety of different chemical groups
how is a peptide bond formed
condensation reaction- water is made by combining an –OH from the carboxyl group of one amino acid with an –H from the amino group of another amino acid
the two amino acids then become linked by a new peptide bond between the carbon atom or one amino acid and the nitrogen atom of the other
how are amino acids joined together
by polymerisation then the resulting chain is called a polypeptide
what forms the primary structure of any protein
the sequence of amino acids
what is the sequence of amino acids determined by
DNA
what does the primary structure then determine
determines the subsequent shapes and functions- any change can lead to a change of shape
what groups are either side of the peptide bond
both -NH and -C=O groups on either side
what charge does the -NH group have
positive charge
what charge does the O from the -C=O group have
negative charge
what bond does the -NH and -C=O group form
hydrogen bonds
what do the -NH and -C=O groups cause
causes the long peptide chain to be twisted into a 3-D shape, such as the coil known as an a-helix
what can the a-helix be twisted to and folded to give
the complex and specific 3D structure of proteins where the bonds that occur depend on the primary structure of the protein
what bonds are included in the tertiary structure
disulfide- fairly strong and not easily broken
ionic- formed between any carboxyl and amino groups that are not involved in forming peptide bonds. they are weaker that disulfide bonds and are easily broken by pH changes
hydrogen- numerous but easily broken
what do quaternary structure form
complex molecules containing a number of individual polypeptide chains that are linked in various ways
may also be non-protein groups associated with the molecules such as the iron-containing haem group in haemoglobin
what is the test for proteins
- place a sample of the solution to be tested in a test tube and add an equal volume of sodium hydroxide solution at room temperature
- add a few drops of very dilute (0.05%) copper (II) sulfate solution and mix gently
- a purple coloration indicates the presence of peptide bonds and hence a protein. no protein, the solution remains blue
what do enzymes do when there catalysts
alter the rate of reaction with no changes to themselves
can be reused repeatedly and are therefore effective in small amounts
globular proteins
what must happen for small reactions to take place (substrates)
-substrates must collide with sufficient energy to alter the arrangement of their atoms
-free energy of the products must be less than that of the substrates
-need to exceed the minimum amount of energy to activate the reaction. activation energy
-enzymes lower the activation energy needed to start the reaction
what is the active site
the specific region of the enzymes is functional
what is the active site made up of
small number of amino acids
what does the active site form
small depression within the much large molecule
what’s formed when enzymes act on substrates
it fits neatly in this depression and forms an enzymes-substrate complex
in the enzyme-substrate complex what is this held in place by
by bonds that temporarily form between certain amino acids of the active sites and groups on the substrate molecules
what does the induced fit model of enzyme action propose
-that the proximity of the substrate leads to a change in the enzymes that forms the functional active site
-the enzyme is flexible and can mould itself around the substrate
-as it changes shape the enzymes puts a strain on the substrate molecules, which distorts a particular bond or bonds in the substrate which lowers the activation energy needed to break the bond
from measuring enzyme-catalysed reactions what are two changes most frequently measured
-the formation of the products of the reaction.
-the disappearance of the substrate
for an enzyme to work what must it do
-come into physical contact with its substrate
-have an active site which fits the substrate
what is the effect of temperature on enzyme action
-rise in temperature increases the kinetic energy of molecules
-this means that the enzyme and substrate molecules come together more often
-temperature rise also begins to cause the hydrogen and other bond in the enzyme to break
-the enzyme and active site changes shape
-at first the substrate doesn’t fit as well into the active site
-at some point the enzyme is so disrupted that it stops working all together. It has denatured
-this is a permanent change
what is the effect of pH on enzyme action
-pH of a solution is a measure of its hydrogen ion concentration
-the pH of a solution is calculated using the formula pH= -log10(H+)
-a hydrogen ion concentration of 1x10-9 therefore has a pH of 9
-the pH affects how an enzyme works in the following ways:
a change in pH alters the charges on the amino acids that make up the active site of the enzyme. The substrate can no longer become attached to the active site and so the enzyme-substrate complex cannot be formed
-depending on how significant the change in pH is, it may cause the bonds maintaining the tertiary structure to break
-H+ ions affects the ionic and hydrogen bonds between –NH2 and –COOH.
what are competitive inhibitors
-have a similar molecular shape similar to that of the substrate
-they compete with the substrate for the available active sites
-increasing the substrate concentration, decreases the effect of the inhibitor
-the inhibitor is not permanently bound to the active site
what are non-competitive inhibitors
-attach themselves to the enzyme at a binding site which is not the active site.
-upon attaching to the enzyme the inhibitor alters the shape of the enzyme and thus its active site in such a way that substrate molecules can no longer occupy it
-an increase in substrate concentration does not decrease the effect of the inhibitor
