B1 Flashcards
the carbon atom’s features that allow organic molecules to be formed
carbon atoms readily form bonds with other carbon atoms to make a carbon backbone along which other atoms can attach
in living organisms, there are relatively few other atoms that can attach to carbon
life is therefore based on a small number of chemical elements
monosaccharide
basic carbohydrate monomer
sweet tasting
soluble
(CH2O)n - n=3-7
can form crystals
affect water potential
e.g. glucose, fructose, galactose
glucose
hexose sugar
C6H12O6
two isomers: a and B gluclose
- they differ in the position of -OH attached to C1
in B glucose, the H is below the plane and the -OH is above the plane on C1
disaccharides
two monosaccharides join in s condensation reaction
forms a glycosidic bond
addition of water breaks glycosidic bond- hydrolysis
glucose+glucose = maltose a1-4
glucose+fructose = sucrose
glucose+galactose = lactose B1-4
polysaccharides
polymers, made by combining many monosaccharide molecules, joined by glycosidic bonds in condensation
large molecules
insoluble in water
not sweet
does not affect water potential
Cx(H2O)y
polysaccharides differ in:
constituent monomers
type of bond
where the glycosidic bond is (polysaccharides)
structure (helical/branched)
function
where they are found
uses of a + B glucose
a-glucose: respiratory processes + energy storage
B-glucose: strength, rigidity, support
test for starch
place sample in test tube
add drops of iodine in potassium iodide solution
positive result = yellow –> blue/black
condensation
joins monomers together
forms a chemical bond
releases water
hydrolysis
breaks a chemical bond between monomers
uses water
starch- about + structure
polysaccharide found in plants in small grains
esp in seed and storage organs
major energy source in most diets
- made up of chains of a-glucose, linked by a 1-4 glycosidic bonds, in condensation reactions
- branched chains- amylopectin
- unbranched chains- amylose
amylose = wound in tight coil- compact helical structure
starch structure to function
- insoluble- doesnt affect water potential
- large- does not diffuse out of cells
- amylose = compact- lots stored in small space
- hydrolysed to a-glucose- used in respiration
- branched amylopectin- many ends increase surface are - which can be acted on by enzymes- releasing a-glucose - monomers readily for respiration
glycogen about + structure
found in animals and bacteria, never plant
similar structure to amylopectin, but shorter chains, more highly branched
‘animal starch’- major carbs storage molecule in animals
glycogen structure to function
- insoluble- does not affect water potential
- large- does not diffuse out of cells
- compact- lots stored in small space
- more highly branched than starch- more ends can be acted on simultaneously by enzymes- rapidly hydrolysed to glucose monomers- used in respiration
this is important to animals which have a higher metabolic rate and therefore respiratory rate than plants because they are more active
suggest how glycogen acts as a source of energy
hydrolysed to glucose monomers
used in respiration
cellulose - structure + function
made of B-glucose monomers
- long, straight unbranched chains
- chains run parallel to each other
- hydrogen bonds form cross linkages between adjacent chains
- number of hydrogen bonds adds much strength
- unlike starch, adjacent glucose molecules are rotated 180 degrees
this allows hydrogen bonds to form between -OH groups on adjacent parallel chains
cellulose molecules grouped together –> microfibrils –> fibres
how does cellulose support plant cells
provides rigidity to plant cell wall that prevents cell bursting when water enters by osmosis
- exerts inwards pressure that stops further influx of water
- living plant cells are turgid and semi-rigid
important in maintaining stems and leaves in a turgid state so they can provide maximum surface area for photosynthesis
explain how the structure of starch and cellulose are different
starch made of a-glucose
cellulose made of B-glucose
position of -OH on C1 = inverted in cellulose
characteristics of lipids
contain C, H, O
proportion of O to C and H is smaller than in carbohydrates- long fatty acid hydrocarbon chain
insoluble in water
soluble in organic solvents e.g. alcohols and acetone
roles of lipids
- cell surface membrane and membrane surrounding organelles
phospholipids contribute to the flexibility of membranes and the transfer of lipid soluble substances across them
-source of energy: when oxidised, provide more than twice the energy as same mass of carbs + release water
-waterproofing: insoluble in water- plants and insects have thick waxy cuticles to conserve water, mammals produce oily secretion from sebaceous glands
-insulation: slow conductors of heat- retain body heat. also electrical insulators in myelin sheath around nerve cells
-protection: stored around delicate organs
hydrogenated fatty acids
formed when acids with C=C are bombarded with H so they become saturated
triglyceride structure
have three fatty acids combined with glycerol
each fatty acid forms an ester bond with glycerol in a condensation reaction (-OH + -COOH)
simple triglyceride
fatty acids all the same
mixed triglyceride
different fatty acids
saturated/monounsaturated/polyunsaturated fatty acid
no C=C/ 1 C=C/ many C=C
structure of fatty acids related to properties
2 saturated, 1 unsaturated
kinky
cannot stack ontop of each other
liquid @ room temp
e.g. oils
3 saturated
can stack ontop of each other
solid @ room temp
e.g. fat
triglyceride structure related to properties
- high ratio of C-H to C (fatty acid) so excellent energy soure
- low mass to energy ratio- good storage molecule, much energy stored in a small volume- reduces mass animals need to carry around
- large, non-polar so insoluble in water- does not affect water potential
- release H2O when oxidised
phospholipid structure
differ from triglyceride- one fatty acid molecule replaced by phosophate molecule
hydrophilic head, hydrophobic tail
structure of phospholipids related to function
- polar molecules- in aqueous environment, form hydrophobic bilayer within cell-surface membranes
- hydrophobic heads hold surface of cell-surface membrane
- can form glycolipids within cell surface membranes- cell recognition
test for lipids
add ethanpl to sample
shake to dissole
add water
shake gently
milky white emulsion = positive
milky colour = due to any lipid being finely dispersed in water to form emulsion
light is refracted as it passes oil-water so appears cloudy
benedicts test
reducing + non reducing
reducing
- grind with pestle + mortar
- add water
- filter out solid
- add benedicts
- gently heat with water bath
- blue to brick red
non reducing
- if reducing = negative
- new sample, add HCl
- boil
- add alkali to neutralise
- add benedicts
- heat gently
- blue to brick red
non subjective approach to benedicts
filter out precipitate and dry
weigh ppt
the higher the mass, the more sugar present
describe how an ester bond is formed in a phosphodiester molecule
condensation reaction
loss of water
between glycerol and fatty acid
explain how cellulose molecules are adapted to their function
long straight chains
linked by many hydrogen bonds
to form fibrils
grouped to fibres
provide strength to cell walls
explain how starch molecules are adapted for their function
insoluble- doesnt affect water potential
helical- compact
large molecule- cannot leave cell
why do polar molecules dissolve in water?
polar molecules form hydrogen bonds with water molecules
what is a macromolecule and how is it formed
large molecule consisting of thousands of carbon atoms joined together
(polymers = molecules)
formed by condensation reactions
why does sucrose produce a positive benedicts test after acid hydrolysis
acid hydrolysis of sucrose molecules releases the monomers a-glucose and b-fructose
the monomers are reducing sugars
give a positive result when heated with benedicts reagent
plant cell walls structire to function
contain cellulose
exerts inward pressure on cell contents
prevents further influx of water
therefore cells do not burst when HYDROSTATIC PRESSURE increases
why are starch and glycogen good for storage
both virtually insoluble
they DO NOT ADD TO THE SOLUTE CONC in cells
so water potential is not affected
what is an emulsion
particles of a substance that are not dissolved but dispersed in a volume of water
what are amino acids/ polypeptides/ proteins
amino acids are the monomer which combine through condensation and formation of peptide bonds to form the polymer polypeptide
polypeptides can combine to form proteins
proteins have a FUNCTION
structure of amino acids
central (alpha) carbon atom attached to:
- amino group (-NH2)
- carboxyl group (-COOH)
- -H atom
- R group
formation of peptide bond
-OH of carboxyl combines with -H of amino group of another amino acid
why are amino acids zwitterions?
can internally transfer ions
H from COOH –> NH2
net charge of 0
primary protein structure
the amino acid sequence in its polypeptide chain
this sequence determines its shape, properties, function
secondary protein structure
the shape which the polypeptide chain forms as a result of hydrogen bonding
the linked aa possess -NH and -C=O on either side of peptide bond
H of -NH has 8+, O of C=O has 8- (due to high electronegativity of O and N)
these groups form hydrogen bonds
shape : a-helix or B pleated sheet
tertiary protein structure
due to the bending and twisting of the polypeptide helix into a compact structure
disulfide, ionic, hydrogen bonds present, as well as hydrophobic interactions
it is the 3D shape of a protein that is important in terms of its function
it makes each protein distinctive and allows it to recogise/ be recognised by other molecules
quaternary protein structure
combination of many different polypeptide chains and associated non protein prosthetic groups into a large, complex protein molecule (conjugated)
test for proteins
biruret test- detects peptide bonds
- place sample in test tube
- add equal volume NaOH
- add few drops CuSO4 and mix
blue to purple is positive
fiborous proteins structure + functions
unbranched
tightly wound
tertiary structure twisted in second helix to make quaternary
water insoluble
physically tough
parallel polypeptide chains in long fibres
functions
structural role + contractile
globular protein structure + functions
roughy spherical
water soluble
tertiary structure critical for function
polypeptide chains folded into a spherical shape
functions
metabolic
catalytic
regulatory
transport
protective
what are enzymes
enzymes are globular proteins that act as catalysts
they alter the rate of a chemical reaction without undergoing a permanent change themelves
what conditions must be satisfied for a reaction to take place
- the reactants must collide with sufficient energy to alter the arrangement of their atoms
- the free energy of the products must be less than that of the substrates
- activation energy must be reached
how do enzymes lower the activation energy
breaking bonds
bringing molecules together
enzyme structure
globular proteins
specific 3D structure as a result of primary protein structure
functional region called active site
- the specific region of the enzyme where the substrate binds and catalysis takes place
substrate
the molecule on which the enzyme acts
active site + enzyme are complementary shape
forms enzyme-substrate complex
substrate is held in active site by bonds that temporarily form between certain a.a in the active site and the groups on the substrate molecule
how is substrate held in active site
R-groups of amino acids face inside the active site
- made up of +ve and -ve charges
- bonds temporarily form between a.a. and substrate
- helps substrate settle in active site
what is enzyme specificity
enzyme only catalyses reaction with substrates with complementary shapes
induced fit model
proximity of substrate
enzyme changes shape
substrate in active site
enzyme puts strain on substrate
distorts bonds in substrate
lowers activation energy needed to break bonds
lock and key model
an enzyme only fits the shape of 1 specific substrate - the enzyme is highly specific and rigid
limitation of lock and key
enzymes are not rigid structures
- other molecules can bind to the enzyme, NOT on the active site (e.g. non competitive inhibitors) and alter the active site shape
- enzymes are therefore flexible structures
so:
if an inhibitor binds to enzyme (not act. site), the active site shape distorts and the substrate cannot fit
- therefore, the active site changes depending on bonding molecules to the enzyme
measuring enzyme catalysed reactions
use its time course:
rate = amount/time
amount = mass or volume
disappearance of substrate or formation of product
the rate of an enzyme catalysed reaction (stages)
- lots of substrate, 0 product
-easy for substrate to meet empty active sites
-all active sites are filled at one time
-amount of substrate decreases as its broken down
-amount of product increases
-becomes more difficult for substrate to come into contact with enzyme- fewer substrate molecules as broken down, and product molecules get in the way.
-substrate molecules take longer to be broken down and rate of reaction slows
-rate continues to slow as substrate concentration decreases
-until substrate concentration is so low so that any more change its concentration cannot be measured.
-until no substrate left so rate stops
how to measure the rate of an enzymes catalysed reaction
tangent to curve
effect of temperature on enzyme action
- increasing temperature increases kinetic energy of molecules
they move around more rapidly and collide more often
more enzyme substrate complexes formed so rate increases - increasing temperature further begins to cause hydrogen bonds to break- change in tertiary structure
active site changes shape- substrate fits less easily - increasing temperature further (around 60 degrees) the enzyme is so disrupted that it completely denatures and stops working.
denaturation is a permanent change- enzyme is no longer functional
why is our body temperature not higher for increased enzyme action
although higher body temperature would increase the metabolic rate slightly
advantages offset by additional energy that would be needed to maintain the higher temperatures
other proteins, apart from enzymes, may be denatured at higher temperatures
at higher temperatures, any further rise in temperatures e.g. during illness, may denature the enzymes
why do different species have different body temperatures
some animals e.g. birds have a normal body temperature of around 40 degrees because they have a high metabolic rate for the high energy requirement of flight
when describing a rate / temp graph
- where it starts
- where it peaks- optimum temp
- where it goes down
- where it ends
effect of pH on enzyme action
pH is a measure of H= conc
each enzyme has optimum pH
at a different pH than the optimum, the H bonds in the active site are broken- enzyme denatires
change in pH also alters the charges on amino acids in the active site- so it is no longer complementary
can also break ionic+hydrogen bonds in the tertiary structure so the active site changes shape
temp + pH- pattern of marks
- identify bonds
- state effect on tertiary structure of active site
- decrease in the number of enzyme substrate complexes forming
loss of complimentary shapes - denaturation
reduction of rate of reaction
effect of enzyme concentration on rate
as long as excess substrate, increase in enzyme conc leads to proportionate increase in rate of reaction
graph initially shows proportionate increase
- because there is more substrate than the enzyme’s active sites can cope with
- increasing enzyme concentration, some excess substrate can be acted upon so rate increases
if substrate is limiting (i.e. not sufficient substrate to supply all active sites) any increase in enzyme conc will have no effect on rate
rate will stabilize at constant level
because available substrate is already being used as rapidly as it can be by existing enzyme molecules
effect of substrate concentration on rate
if enzyme conc = fixed and substrate conc increased, rate increases in proportion
- at low substrate conc, enzyme molecules have limited number of substrate molecules to collide with so active sites are not working at full capacity
- as more substrate added, active sites gradually become filled, until max rate Vmax
when substrate is in excess, rate levels off
inhibitor
a substance which reduces the activity of an enzyme, catalyst or reactant
enzyme inhibitor
substances that directly or indirectly interfere with the functioning of the active site of an enzyme and so reduce its activity
types of enzyme inhibitors
competitive- bind to active site
non competitive- bind to enzyme at a position other than the active site
competitive inhibitor properties
- similar molecular shape to substrate
allows them to occupy active site
it is the difference between the concentrations of the inhibitor and substrate that determines the effect on enzyme activity
if the substrate conc is increased, effect of inhibitor is reduced
the inhibitor is NOT PERMANENTLY BOUND to the active site so when it leaves another molecule can take its place
sooner or later, all substrate molecules will occupy an active site, but the greater the concentration of inhibitor, the longer this will take
non competitive inhibitor
attach to enzyme at binding site which isnt active site
upon attachment, alters shape of enzyme and thus its active site so that it is no longer complementary to substrate
a PERMANENT change to shape of enzyme
as the substrate and inhibitor are not competing, increase in substrate concentration does not decrease effect of inhibitor
eventually no enzyme substrate complexes formed
what is a metabolic pathway
a series of reactions in which each step is catalysed by an enzyme
each reaction is connected by their intermediates i.e. the product of one is the reactant of the next
how are metabolic pathways structured
the enzymes that control a pathway are often attached to the membrane of a cell organelle in a precise sequence.
- in a metabolic pathway, the product of one reaction acts as a substrate for the next
- by having the enzymes in an appropriate sequence, there is a greater change of each enzyme coming into contact with its substrate than if the enzymes were free in the organelle
this is a more efficient means of producing the end product
to keep a steady concentration of a particular chemical in a cell, the same chemical often acts as an inhibitor of an enzyme at the start of a reaction,
end product inhibition
end product inhibits 1st enzyme
if the concentration of end product increases above normal, there will be greater inhibition of 1st enzyme
as a result, less product will be produced and its concentration will return to normal
if the concentration of the end product falls below normal, there will be less to inhibit 1st enzyme
so more product produced
end product inhibition is normally non competitive
suggest one advantage of end product inhibition being non competitive
relate your answer to how the two types of inhibition take place
- the level of end product does not fluctuate with substrate
non- competitive inhibitors occur at a site on the enzyme other than the active site-
hence isnt affected by substrate concentration
therefore in non-competitive inhibition, changes in the level of substrate do not affect the level of inhibitor, nor the level of end product
competitive inhibition involves competition for active sites
a change in the level of substrate would therefore affect how many end products molecules combine with active sites
therefore the degree of inhibition would fluctuate and so would the level of end product.
