2.3 Carbohydrate and Lipid Flashcards
What are carbohydrates made of?
Carbohydrates are made of C, H and O (‘carbo’ – contains carbon ; ‘hydrate’ – contains H and O)
What are carbohydrates made of?
Carbohydrates are composed of recurring monomers called monosaccharides (which typically form ring structures)
What reaction links monosaccharides?
These monosaccharides may be linked together via condensation reactions (water is formed as a by-product)
What bond links two monosaccharides?
Two monosaccharide monomers may be joined via a glycosidic linkage to form a disaccharide
What is it called when many monosaccharides join together?
Many monosaccharide monomers may be joined via glycosidic linkages to form polysaccharides
What are monosaccahrides? (e.g function)
Monosaccharides (one sugar unit) are typically sweet-tasting and function as an immediate energy source for cells
What are examples of monosaccharides?
Examples of monosaccharides include glucose, galactose and fructose
What are disaccharides?
Disaccharides (two sugar units) are small enough to be soluble in water and commonly function as a transport form
What are examples of disaccharides?
Examples of disaccharides include lactose, maltose and sucrose
What is the role of polysaccharides?
Polysaccharides (many sugar units) may be used for energy storage or cell structure, and also play a role in cell recognition
What are examples of polysaccharides?
Examples of polysaccharides include cellulose, glycogen and starch
What are polysaccharides made of?
Polysaccharides are carbohydrate polymers comprised of many (hundreds to thousands) monosaccharide monomers
What does the type of carbohydrate polymer depend on?
The type of polymer formed depends on the monosaccharide subunits involved and the bonding arrangement between them
What 3 types of polymers can be made from glucose monomers?
Three key polymers can be made from glucose monosaccharides – cellulose, starch (in plants) and glycogen (in animals)
What is cellulose?
Cellulose is a structural polysaccharide that is found in the cell wall of plants
What is the structure of cellulose?
It is a linear molecule composed of β-glucose subunits (bound in a 1-4 arrangement)
Why can animals not digest cellulose?
Because it is composed of β-glucose, it is indigestible for most animals (lack the enzyme required to break it down)
What 2 organisms can consume cellulose?
Ruminants (e.g. cows) may digest cellulose due to the presence of helpful bacteria in a specialised stomach
Caecotrophs (e.g. rabbits) will re-ingest specialised faeces that contain digested cellulose (broken down in the caecum)
Where is starch found and what is its function?
Starch is an energy storage polysaccharide found in plants
What Is starch composed of?
It is composed of α-glucose subunits (bound in a 1-4 arrangement)
What 2 forms does starch take?
exists in one of two forms – amylose or amylopectin
What is the structure of amylose?
Amylose is a linear (helical) molecule
What is the structure of amylopectin?
amylopectin is branched (contains additional 1-6 linkages)
Which form of starch is preferred and why?
Amylose is harder to digest and less soluble, however, as it takes up less space, is the preferred storage form in plants
What is glycogen?
Glycogen is an energy storage polysaccharide formed in the liver in animals
What is the structure of glycogen?
It is composed of α-glucose subunits linked together by both 1-4 linkages and 1-6 linkages (branching)
What molecule is glycogen similar to?
It is akin to amylopectin in plants but is more highly branched (1-6 linkages occur every ~10 subunits as opposed to ~20)
What are fatty acids?
Fatty acids are long hydrocarbon chains that are found in certain types of lipids (triglycerides & phospholipids)
Can fatty acids differ?
YES
Fatty acids may differ in the length of the hydrocarbon chain (typically 4 – 24 carbons) and in the number of double bonds
What are saturated fatty acids?
Fatty acids that possess no double bonds are saturated (have maximum number of H atoms)
What are 3 main properties of saturated fatty acids?
Saturated fatty acids are linear in structure, originate from animal sources (i.e. fats) and are typically solid at room temperatures
What are unsaturated fatty acids?
Fatty acids with double bonds are unsaturated – either monounsaturated (1 double bond) or polyunsaturated (>1 double bond)
What are the 3 main properties of unsaturated fatty acids?
Unsaturated fatty acids are bent in structure, originate from plant sources (i.e. oils) and are typically liquid at room temperatures
In what 2 forms can unsaturated fats come in?
Unsaturated fatty acids may occur in two distinct structural configurations – cis and trans isomers
What does it mean if a fatty acid is cis?
Cis: The hydrogen atoms attached to the carbon double bond are on the same side
What does it mean if a fatty acid is trans?
Trans: The hydrogen atoms attached to the carbon double bond are on different sides
Are trans fatty acids common?
Trans fatty acids do not commonly occur in nature and are typically produced by an industrial process called hydrogenation
What structure do trans fatty acids have?
Trans fatty acids are generally linear in structure (despite being unsaturated) and are usually solid at room temperature
What are triglycerides?
Triglycerides are the largest class of lipids and function primarily as long-term energy storage molecules
In what form do animals store triglycerides?
Animals tend to store triglycerides as fats (solid)
In what form do plants store triglycerides?
plants tend to store triglycerides as oils (liquid)
How are triglycerides formed?
Triglycerides are formed when condensation reactions occur between one glycerol and three fatty acids
What happens in a condensation reaction in triglycerides?
The hydroxyl groups of glycerol combine with the carboxyl groups of the fatty acids to form an ester linkage
What molecule is formed apart from the triglyceride in a condensation reaction?
This condensation reaction results in the formation of three molecules of water
What two forms can triglycerides take and what does it depend on?
Triglycerides can be either saturated or unsaturated, depending on the composition of the fatty acid chains
Are any fats (in excess) “healthy?
all types of fats consumed as part of dietary intake will cause adverse health effects if taken in excessive amounts
What does fat affect in the bloodstream?
The mix of fats in the diet influences the level of cholesterol in the bloodstream
What 2 types of fats raise blood cholesterol levels?
Saturated fats and trans fats raise blood cholesterol levels,
What 2 types of fats lower blood cholesterol levels?
(cis) unsaturated fats lower blood cholesterol levels
Can fats and cholesterol be transported in the blood?
NO
Fats and cholesterol cannot dissolve in blood and are consequently packaged with proteins (to form lipoproteins) for transport
What do low-density lipoproteins carry?
Low density lipoproteins (LDL) carry cholesterol from the liver to the rest of the body
What do high density lipoproteins carry?
High density lipoproteins (HDL) scavenge excess cholesterol and carry it back to the liver for disposal
Are LDL’s or HDL’s “good” for health?
Hence LDLs raise blood cholesterol levels (‘bad’) while HDLs lower blood cholesterol levels (‘good’)
How do saturated fats affect the level of cholesterol in the blood?
Saturated fats increase LDL levels within the body, raising blood cholesterol levels
How do trans fats affect the level of cholesterol in the blood?
Trans fats increase LDL levels and decrease HDL levels within the body, significantly raising blood cholesterol levels
How do unsaturated (cis) fats affect the level of cholesterol in the blood?
Unsaturated (cis) fats increase HDL levels within the body, lowering blood cholesterol levels
What is the risk of high cholesterol?
High cholesterol levels in the bloodstream lead to the hardening and narrowing of arteries (atherosclerosis)
What will happen when there are high levels of LDL in the blood?
When there are high levels of LDL in the bloodstream, the LDL particles will form deposits in the walls of the arteries
What does the accumulation of fat in the arteries cause?
The accumulation of fat within the arterial walls lead to the development of plaques which restrict blood flow
What is the final result of high blood cholesterol?
If coronary arteries become blocked, coronary heart disease (CHD) will result – this includes heart attacks and strokes
What are the 2 main health claims about lipids in the diet?
Diets rich in saturated fats and trans fats increase the risk of CHD
Diets rich in monounsaturated and polyunsaturated (cis) fats decrease the risk of CHD
Where is the evidence for the effect of fats on the body gathered?
Epidemiological studies comparing different population groups
Intervention studies that monitor cohorts following dietary modifications
Experimental designs utilising animal models or data based on autopsies
Lipids and health counter and pro arguments?
Evidence Supporting Health Claims
A positive correlation has been found between the intake of saturated fats and the incidence of CHD in human populations
Counter: 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)
Intervention studies have shown that lowering dietary intakes of saturated fats reduces factors associated with the development of CHD (e.g. blood cholesterol levels, blood pressure, etc.)
Counter: Validity of intervention studies is dependent on size and composition of cohort, as well as the duration of the study
In patients who died from CHD, fatty deposits in diseased arteries were found to contain high concentrations of trans fats
Counter: Genetic factors may play a role (e.g. blood cholesterol levels only show a weak association to dietary levels)
Evidence Against Health Claims
Proportion of saturated and trans fats in Western diets has decreased over the last 50 years, but incidence of CHD has risen
Counter: Increased carbohydrate intake may cause detrimental health effects associated with CHD (e.g. diabetes, obesity)
Counter: Incidence of CHD dependent on a myriad of factors besides dietary intake (e.g. exercise, access to health care, etc.)
In what 5 ways do lipids and carbohydrates differ in function?
Storage Osmolarity Digestion ATP yield Solubility
In what way do lipids and carbohydrates differ in terms of storage?
lipids are more suitable for long-term energy storage
In what way do lipids and carbohydrates differ in terms of osmolarity?
lipids have less of an effect on the osmotic pressure of a cell
In what way do lipids and carbohydrates differ in terms of digestion?
carbohydrates are easier to digest and utilise
In what way do lipids and carbohydrates differ in terms of ATP yield?
(lipids store more energy per gram
In what way do lipids and carbohydrates differ in terms of solubility?
carbohydrates are easier to transport in the bloodstream
What is the BMI?
The body mass index (BMI) provides a measure of relative mass based on the weight and height of the individual
What is the formula for BM!?
BMI = mass in kg/ height in m ^2
What do BMI values range from?
BMI ranges from underweight to obese, according to predetermined values based on an average adult population
When are BMI’s not valid?
BMI values are not a valid indicator for pregnant women or professional athletes with atypical muscle / fat ratios
Can BMI’s by themselves be used as a diagnostic tool?
BMI calculations should not be used as a diagnostic tool and should be used in conjunction with other measurements
What is another way to calculate body mass index?
An alternative way of calculating body mass index is by using an alignment chart (nomogram
What is a nonogram?
Nomograms display height and weight on perpendicular axes and then assign BMI values to colour coded regions
