Metabolism & Metabolic Pathways Flashcards
Understand roles of metabolites and different metabolic pathways in energy production (22 cards)
Structure of carbohydrates
Composed of carbon, hydrogen and oxygen - C(H2O)n
Classified as Monosaccharide (1 unit), Disaccharide (2), Oligosaccharides (3-10), Polysaccharides (>10)
Monosaccharide isomers e.g. glucose isomers
D-Isomers - a stereoisomer which rotates light that is polarized in a clockwise direction
L-Isomers: a stereoisomer that has a non superimposable mirror image counterpart
Roles of carbohydrates
(1) Source of energy for chemical reactions
(2) inhibits breakdown of proteins for energy use
(3) Fatty acid breakdown and prevention of ketosis
Structure of proteins
Amino acids joined together by peptide bonds to form polypeptide chains
(1) Primary structure: the unique sequence of amino acids that make up a protein or polypeptide chain
(2) Secondary structure: The way in which the primary structure of a polypeptide chain folds. e.g. beta sheets and alpha helixes
(3) Tertiary structure: The final 3D structure of a protein, entailing the shaping of a secondary structure. e.g. antibodies and keratin
(4) Quaternary structure: formed when two or more polypeptide chains join together to form a protein e.g. haemoglobin
Roles of proteins
(1) transport e.g. albumin
(2) hormone signalling
(3) immune functions e.g. antibodies
(4) gene transcription and translation
Structure of lipids
- Made of hydrogen and carbon atoms linked by neutral covalent bonds
- non-polar due to the covalent bond, therefore insoluble in water
Fatty acids
Cis fatty acids: 2 Hydrogen atoms on the same side of the = bond that make membranes more fluid
Trans fatty acid: the 2 hydrogen atoms are on opposite side of = bond
Triglycerides
- 3-C glycerol linked to 3 fatty acids
- A carboxyl group is attached to the hydroxyl group of glycerol
- Unsaturated fatty acids have double bonds (C=C)
- polyunsaturated fatty acids have more than 1 double bone (C-C)
Phospholipids
- Modified triglycerides with one fatty acid replaced by a phosphate group
- Electrically charged phosphate group creates a polar region
- Present in the bilayer of eukaryote cell membrane
Steroids
- 4 interconnected rings of carbon
- Insoluble in water
- Includes sex hormones
Glycolipids
- A carbohydrate attached to one of more fatty acid chains
- Play a key role in cell surface recognition
Ketone bodies
- Formed from oxidation of fatty acids in the liver
- Excessive formation of ketone bodies found in Type I diabetes
- Acetone formed from breakdown of ketone bodies
Roles of Lipids
- Chemical messengers (e.g. glycolipids)
- Energy storage
- Membrane lipid bilayer (e.g. phospholipids)
Glucose and Fatty Acid interactions
- Fatty acids can be formed from glucose, but not vice versa
- glucose can be stored as a lipid
- White adipose tissue is specialised for triglyceride storage
- storage of carbohydrate as glycogen is limited
Glucose Transporters
- Glucose is a polar molecule that is impermeable to the cell membrane
Sodium-Glucose Cotransporters (SLGTs) 1-4
- found in specialised epithelial cells of the small intestine and PCT of kidney
- actively transports glucose by coupling glucose with Na+
- the Na+ gradient is maintained by active transport of Na+ across the Na+K+ ATPase channel
Facilitative Glucose Transporters (GLUTS) 1-5
- mediates an energy independent transport of glucose by facilitated diffusion
Glycolysis
- Breakdown of glucose to form pyruvate and 2 ATP molecules
- Pyruvate can be used in anaerobic respiration or by TCA cycle in presence of oxygen
Glucose Phosphorylation
- Occurs inside the cell by hexokinases
- Hexokinases have higher affinity for glucose transporters therefore utilised more in brain, RBCs and muscles
- Glucokinases have lower affinity for glucose transportes therefore utilised more in liver and pancreatic B cells
Anaerobic respiration
- Glucose is converted to Glucose-6-Phosphate by hexokinase
- Glucose-6-P is converted into Frucose-6-P by phosphofructokinase
- A Pi is added to glyceraldehyde by dehydrogenase
- Pyruvate Kinase allows formation of pyruvate, which can be reduced to lactic acid
- 2 ATP is produce
Tricarboxylic Acid Cycle
- A 2C Acetyl-CoA is combined with oxaloacetate to form citrate
- FADH2 and NADH produced are sent to the electron transport chain
- 4 ATP is produced
Electron Transport Chain
- NADH and FADH2 produced from TCA and Fatty acid B-oxidation are used to produce ATP
- Energy from NADH and FADH2 are used to pump protons across the ATP-ADP carrier channels in the mitochondrial membrane down a concentration gradient
- 36 ATP produced in the presence of oxygen
- 2 ATP produced in the absence of oxygen
- By products include H2O and CO2
- Uncoupling can lead to excessive proton influx and heat generation that may result in cell damage, decrease ATP production and ageing
Energy Substrate Requirement
Glucose: obligatory for brain cells and RBCs
Fatty acids: most tissues
Ketones: most tissues, except in the liver
Amino Acids/Proteins: minimal usage, except in fast dividing cells e.g. in cancer
Amino Acid Metabolism
- AA are used in synthesis of proteins and peptides
- Sources of energy during fasting, trauma and sepsis
- Deamination: removal of an amine group by deaminase enzymes
- Transmination: transfer of an amine group to a ketoacid to make new amino acids
- Urea Formation: removal of the nitrogenous base
