Metabolism 1 Flashcards
What is the general molecular formula for carbohydrates?
[C(H2O)]n (‘hydrated carbon’)
n equal to/> 3
How are carbohydrates classified?
- Monosaccharides (1 monomeric unit)
- Disaccharides (2 monomeric units)
- Oligosaccharides (3-10 monomeric units)
- Polysaccharides (>10 monomeric units)
What types of carbohydrates are in a typical healthy human diet?
Polysaccharides (complex carbohydrates) e.g. starch which need to be broken down in order to be absorbed
What is the suffix ending names of monosaccharides?
‘-ose’
What are the ways in which monosaccharides can be classified?
- No. of C atoms (size) e.g. triose, tetrose, pentose, hexose
- Isomer (same atoms but bonded in a different 3D arrangement) e.g. D vs L
What do glucose, fructose and galactose have in common?
They are all hexoses with different arrangements of the same atoms i.e. isomers
What isomer are the most important sugars?
D-isomers
What happens to longer-chain monosaccharides? Give some examples.
They form cyclic molecules pentoses + hexoses (e.g. ribose, glucose)
Pentoses normally form 5-membered rings whilst hexoses form 6-membered rings but this is not always the case as O2 is part of the ring
What are some examples of important monosaccharides? Why are they important?
Trioses: dihydroxyacetone + G3P (important intermediates in energy metabolism i.e. glycolysis)
Pentoses: ribose + deoxyribose (crucial components of RNA + DNA)
Hexoses: glucose, galactose + fructose (found in important disaccharides/oligosaccharides)
How are disaccharides formed?
Reaction between 2 monosaccharides which eliminates H2O + forms a glycosidic bond
What are examples of important disaccharides? How are they formed?
Sucrose = glucose + fructose
Lactose = galactose + glucose
Maltose = glucose + glucose (breakdown product of starch/glycogen)
Give examples of some important poly/oligosaccharides.
Starch (obtained in diet from plant sources)
Cellulose (linear polymer of glucose that is a component of fibre present in diet from plant sources but not digestible in humans due to lack of cellulase enzyme)
Glycogen (extensively branched polymer of glucose obtained in diet from animal sources)
Dextrin (branched oligomer of glucose that is a breakdown product of starch + glycogen)
What is starch made up of?
75% amylopectin (branched polymer of glucose formed by α-1,4 + α-1,6 glycosidic bonds)
25% amylose (linear polymer of glucose formed by α-1,4 glycosidic bonds only)
What are the main types of biologically important lipids?
FAs
Triglycerides (TAGs)
Cholesterol
Cholesterol esters
What are fatty acids?
Hydrocarbon chains of various lengths
How are fatty acids classified?
Considered long chain if >12C + very long chain if >22C
Saturated or unsaturated (at least 1 C=C bond)
Fatty acids + ___ = triglycerides
Glycerol
What are the different types of fatty acid nomenclature?
- Most descriptive: C#1:#2(Δ#,#…) - #1 (total no. of Cs), #2 (no. of double bonds) + numbers in brackets (Cs where double bond occurs counting from acidic end)
- Describing position of final double bound from hydrocarbon end: ω-# (‘omega-#’)
What does the cis or trans nomenclature of fatty acids describe?
A form of stereoisomerism at double bounds, around where there is no rotation
(applies to unsaturated FAs)
What is the difference between cis and trans fatty acids?
Either isomer can be incorporated into triglycerides + modified lipids but cis FAs pack next to each other less closely than trans ones causing membranes to be more fluid
What do phospholipids consist of?
A phosphate group attached to 1 or more FA chains via glycerol or sphingosine, which itself contains a long hydrocarbon chain
What do glycolipids consist of?
A carbohydrate element (usually an oligosaccharide) attached to 1 or more FA chains directly or via glycerol or sphingosine
What are the functions of phospholipids and glycolipids?
Important components of cellular membranes:
- Phospholipids amphipathic (polar/non-polar) nature integral to membrane structure
- Glycolipids function in cell surface recognition
What are ketone bodies? Give a couple of examples of them.
Small (4C) FAs formed by oxidation of FAs in the liver especially during fasting, when they become important energy substrates for the brain
E.G. acetoacetic acid + β-hydroxybutyric acid
What can be excessively produced by the liver in type 1 diabetes? What is the consequence of this?
Ketone bodies resulting in dangerously high concentrations in the blood which can cause ketoacidosis
Acetone is formed as a breakdown product + is exhaled - pear drop smell on patient’s breath
What are the roles of lipids?
- Substrates for energy generation in cells e.g. FAs, ketone bodies
- Energy storage e.g. triglycerides
- Transport between tissues e.g. cholesterol esters, triglycerides
- Structural components of cell membranes e.g. phospholipids, cholesterol
- Chemical messengers e.g. diglycerides
What different types of amino acids exist?
- Essential: obtained from diet e.g. Leu, Val, Lys + Phe
2. Non-essential: synthesized endogenously e.g. Ala, Cys, Gly + Ser
How is Adenosine Triphosphate (ATP) made?
From ADP using energy released by oxidation
What is Adenosine Triphosphate (ATP) used for?
Anabolic processes consume it
Catabolic processes produce ATP
What is the difference between anabolism and catabolism?
Energy stored in high-energy bond is released in anabolism whereas in catabolism, energy from oxidation of nutrients is stored in high-energy bond
Where can glucose be used as an energy source?
For most tissues but obligatory for brain + RBCs
Where can fatty acids be used as an energy source?
Most tissues + minimally in neurons
Where can ketones be used as an energy source?
Most tissues but not the liver as this is where they are synthesized
Important for brain as a partial substitute for glucose when less is available
Where can amino acids be used as an energy source?
Not used as fuel by many cell types but used in fast-dividing cells e.g. enterocytes + cancer cells (particularly Glu)
What can happen to glucose once it has been taken into the body?
- Digestive system -> blood where it is taken up by RBCs
- Lactate is produced + so is energy as a by-product of the reaction
- If there is lots in the blood, it can be taken to liver to be stored as glycogen (main storage) which can be broken down again when hungry/starving
- Used as an energy source by the brain + muscle (skeletal + cardiac) too
- If broken down with insufficient O2 when exerting yourself, lactate is formed which can be recycled in liver to form new glucose
How do fatty acids and glucose interact?
Mechanisms exist for minimising utilisation of both glucose + FAs at the same time
FAs can be formed from glucose but NOT vice versa so glucose excess can be stored as lipid (triglycerides) but this can only be mobilised/metabolised as FAs
Where should triglycerides be stored? What happens if other tissues start to store it?
White adipose tissue (internal or subcutaneous)
Spill over into ‘ectopic’ tissues e.g. skeletal/cardiac muscle + liver has pathological consequences
Where are carbohydrates?
Storage as glycogen is limited in extent:
- In liver to regulate blood glucose (lasts overnight in humans)
- In skeletal muscle for direct energy requirements
How is glucose transported into cells?
- Passive transport via GLUT1-5
2. Active transport via SGLT-1 + 2
What is the specificity and tissue distribution of GLUT1? What is its main role?
Transports glucose, galactose + mannose
Present in RBCs, brain + ubiquitously
Involved in basal uptake as it has high affinity for glucose
What is the specificity and tissue distribution of GLUT2? What is its main role?
Transports glucose + fructose
Present in liver + pancreatic β cells
Involved in glucose sensing due to low affinity for glucose
What is the specificity and tissue distribution of GLUT3?
Transports glucose only
Present in brain, intestine + placenta
What is the specificity and tissue distribution of GLUT4? What is its main role?
Transports glucose only
Present in muscle (skeletal/cardiac) + adipose tissue
Insulin sensitive glucose uptake so good at regulation of glucose levels
What is the specificity and tissue distribution of GLUT5?
Transports fructose only
Present in intestine
What is the specificity and tissue distribution of the SGLT glucose transporters?
SGLT1: transports 2 glucose, Na + galactose & present in intestine/kidney
SGLT2: Transports 2 glucose + Na & present in kidney
