topic 2.3- carbohydrates and lipids Flashcards
give the two main functions of carbohydrates in organisms
- serve as energy sources
- provide support in structures (eg cell wall)
what elements are carbohydrates composed of?
carbon, hydrogen, oxygen
name the three groups of carbohydrates from shortest term energy source and longest term energy source
- monosaccharides
- disaccharides
- polysaccharides
define monosaccharides
single sugar units
define disaccharides
two monosaccharides linked together
define polysaccharides
many monosaccharides linked together
give 3 examples of monosaccharides
glucose, fructose, galactose
give 3 examples of disaccharides
maltose, sucrose, lactose
give 3 examples of polysaccharides
starch, glycogen, cellulose
what are the three different types of monosaccharides?
- trioses (monosaccharides with 3 carbon atoms, eg glyceraldehyde)
- pentoses (monosaccharides with 5 carbon atoms, eg deoxyribose)
- hexoses (monosaccharides with 6 carbon atoms, eg glucose)
what two features are monosaccharides characterised by?
- a hydroxyl group (OH)
- a carbonyl group (C=O)
what is the difference between an aldehyde and a ketone?
- aldehyde has variable group R and hydrogen bonded to C
- ketone has two variable groups R bonded to C
state the general formula for monosaccharides
CnH2nOn
what are ribose and deoxyribose?
they are pentoses and isomers of each other
what are isomers?
molecules with the same molecular formula but different displayed formula
state the 4 important hexoses
- alpha glucose
- beta glucose
- fructose
- galactose
(all isomers)
what is the reaction forming a disaccharide from a monosaccharide called and why?
condensation reaction- water is released
what bond is formed between two monosaccharides when a disaccharide is created?
glycosidic bond
what is the reaction breaking down a disaccharide into two monosaccharides called and why?
hydrolysis- water is being added
what types of processes are condensation/hydrolysis reactions?
condensation- anabolic- energy is used as bonds are being formed
hydrolysis- catabolic- energy is being released as bonds are being broken
what reaction forms polysaccharides from monosaccharides?
condensation polymerisation
what are the three most biologically significant polysaccharides?
starch, cellulose, glycogen
starch, cellulose, glycogen:
- main similarity?
- two differences?
all polymers of glucose but the isomer (alpha/beta) and type of bond (1,4 or 1,6) vary.
how are cellulose chains held together?
by the hydrogen bonds formed between hydroxyl groups and hydrogen in parallel chains.
describe a cellulose molecule
cellulose is a linear molecule
- 1,4 glycosidic bonds give it its linear structure
- beta glucose molecules ONLY
state the features and functions of cellulose in plants
- cellulose microfibrils have high tensile strength
- used as basis of plant cell walls
- prevents cell from bursting due to high water content
what two forms does starch exist in?
amylose and amylopectin
state the two main similarities between amylose and amylopectin
- both are polymers of alpha glucose and are stabilised by hydrogen bonds
- both starches are compact, insoluble and easily hydrolysed
state the main difference between amylose and amylopectin
- amylose is a straight chain, helix shaped molecule containing only 1,4 glycosidic bonds
- amylopectin is a branched molecule as it contains both 1,4 and 1,6 glycosidic bonds
explain the features and functions of starch in plants
molecules are hydrophilic but too large to be soluble in water:
- used as store of glucose in cells where large amounts need to be stored
- made as a temporary store in leaf cells when glucose is being made faster by photosynthesis than it can be exported to other parts of the plant.
what is the function of glycogen?
storage carbohydrate in animals and fungi
describe the structure of glycogen
- polymer of alpha glucose
- highly branched as it contains 1,4 glycosidic bonds along with many 1,6 bonds.
where is glycogen stored in animals?
animals- livers and some muscles
what are lipids?
a diverse group of carbon compounds that share the property of being insoluble in water.
state of fats/oils at body and room temperature
- fats are liquid at body temperature but solid at room temperature
- oils are liquid at both
what elements are present in lipids?
carbon, hydrogen, oxygen
define triglycerides
One of the principal groups of lipids
how is a triglyceride made?
by combining three fatty acids with one glycerol by a condensation reaction
what type of linkage is formed between each fatty acid and the glycerol?
an ester bond
what is the function of triglycerides?
- energy stores
- do not conduct heat well- insulators eg blubber
what are fatty acids?
long hydrocarbon chains with a carboxyl group (COOH) at one end
how do you calculate BMI?
mass in kg/(height in metres)^2
what are the units for BMI?
kg m^-2
state the relationship between BMI and a person’s status
below 18.5- underweight
18.5-24.9- normal weight
25.0-29.9- overweight
30.0 or more- obese
what is a saturated fatty acid?
a fatty acid with single bonds between all of its carbon atoms, that therefore contains as much hydrogen as it possibly could.
what is an unsaturated fatty acid?
a fatty acid that has one or more carbon - carbon double bonds, that therefore contains less hydrogen than it could
what is the difference between a monounsaturated fatty acid and a polyunsaturated fatty acid?
a monounsaturated fatty acid has one carbon-carbon double bond
a polyunsaturated fatty acid has more than one carbon-carbon double bond
what are cis-fatty acids?
unsaturated fatty acids where the hydrogen atoms are on the same side of the two carbon atoms that are double bonded.
what are trans-fatty acids?
unsaturated fatty acids where the hydrogen atoms are on different sides of the two carbon atoms that are double bonded.
explain the features of cis-fatty acids
- there is a bend in the hydrocarbon chain at the double bond
- triglycerides containing these fatty acids are less good at packing together in regular arrays, so this lowers the melting point = usually liquid at room temp
explain the features of trans-fatty acids
- do not have a bend in the hydrocarbon chain at the double bond
- triglycerides containing these fatty acids are good at packing together in regular arrays, so this raises the melting point = usually solid at room temp
are lipids or carbohydrates more suitable for long term energy storage in humans?
lipids
why are lipids more suitable for long term energy storage in terms of mass than carbohydrates?
- amount of energy released in cell respiration per gram of lipids is double the amount released from a gram of carbohydrates
- fats form pure droplets in cells with no water associated, but each gram of glycogen is associated with about 2g of water
=> lipids 6x more efficient in the amount of energy that can be stored per g of body mass (less body mass added)
why are lipids more suitable for long term energy storage in terms of secondary roles than carbohydrates?
- lipids are poor conductors of heat so can act as insulators
- fat is liquid at body temp so it can also act as a shock absorber for organs
why is glycogen ideal for short term energy storage?
- can be broken down into glucose rapidly and then transported easily to where its needed.
- fats in adipose tissue cannot be mobilised as rapidly
- fatty acids can only be used in aerobic respiration
which fats have positive effects on the body?
Unsaturated cis fats:
- increase HDL levels within the body, lowering blood cholesterol levels
which fats have negative effects on the body?
Saturated fats:
- increase LDL levels within the body
Trans fats:
- increase LDL levels and decrease HDL levels within the body
what do LDLs and HDLs do and stand for?
- HDLs (high density lipoproteins) scavenge excess cholesterol and carry it back to the liver for disposal, so lower blood cholesterol levels
- LDLs (low density lipoproteins) carry cholesterol from liver to rest of body, so raise blood cholesterol levels.
what are the health risks of high blood cholesterol levels?
atherosclerosis- narrowing and hardening of arteries
CHD- due to the accumulation of LDL particles in walls of arteries
describe the correlations between fats and CHD
- A positive correlation has been found between the intake of saturated fats and the incidence of CHD in human populations
- In patients who died from CHD, fatty deposits in diseased arteries were found to contain high concentrations of trans fats
counter the claim ‘a positive correlation has been found between the intake of saturated fats and the incidence of CHD in human populations’
certain populations do not fit this trend (e.g. the Maasai tribe in Africa have a fat-rich diet but very low rates of CHD)
counter the claim ‘in patients who died from CHD, fatty deposits in diseased arteries were found to contain high concentrations of trans fats’
genetic factors may play a role (e.g. blood cholesterol levels only show a weak association to dietary levels)
state 3 general counter claims for fats
- validity of intervention studies is dependent on size and composition of cohort, as well as the duration of the study
- increased carbohydrate intake may cause detrimental health effects associated with CHD (e.g. diabetes, obesity)
- incidence of CHD dependent on other factors besides dietary intake (e.g. exercise, access to health care, etc.)
sucrose
alpha glucose and fructose
maltose
- 2x alpha glucose (same way up)
- alpha 1,4 glycosidic bond
lactose
- beta glucose and galactose
- upside down to each other
- beta glycosidic bond
