Intro to metabolism

Question 1

describe ATP

Answer 1

coenzyme, that is acted in by other enzymes
hydrolysis of atp releases energy

Question 2

what are the standard and actual free energies of hydrolysis

Answer 2

the standard free energy of hydrolysis is the amount of energy you get from a mole of ATP, when all the concentrations of ATP, ADP and phosphate are 1 molar (-31kJ/mol)
the actual free energy takes the actual ATP, ADP and phosphate values (-60 kJ/mol)

Question 3

what is the metabolic role of ATP

Answer 3

during oxidation, atp is generated and consumed by energy-consuming reactions
oxidation of glucose, fatty acids and amino acids are broken down to CO2 by the various pathways, liberating energy
ATP is then used in muscle contraction, biosynthetic reactions, ion-pumping, and some of the energy is lost as heat

Question 4

describe NADP

Answer 4

acceptor of hydrogen
derived from vit B3
NADP+ - oxidised form
NADPH - reduced form
anabolic pathways require both energy and reducing power in the form of NADPH

Question 5

metabolic role of NADP

Answer 5

acts as oxidising agent and gets reduced throughout respiration
reduced NADP is reduced and is reoxidised in biosynthetic

Question 6

what are the 4 main categories of dietary requirements

Answer 6

energy (main sources included carbohydrates, fat and protein)
macronutrients
electrolytes and minerals
vitamins

Question 7

how is fat broken down

Answer 7

by the beta-oxidation pathway in the mitochondria

Question 8

how are carbs broken down

Answer 8

glycolysis in cytoplasm and then enters into the mitochondria as pyruvate to be further oxidised

Question 9

how are proteins broken down

Answer 9

digested to 20 differnt amino acids, each of which has at least 1 breakdown pathway, these pathways all end with the intermediate acetyl-CoA, which is the fuel for the citric (tricarboxylic) acid cycle

Question 10

what does the citric acid cycle do

Answer 10

oxidises the acetyl groups into CO2
undergoes oxidative phosphorylation

Question 11

what are starch’s two subcomponents

Answer 11

amylose contains straight chains, in which the glucose units are linked 1-4
amylopectin contains alpha 1-4 linked straight chains with the occasional alpha 1-6 branch

Question 12

overview of starch digestion

Answer 12

begins in saliva where amylase (synthesised by the parotid gland)breaks alpha 1-4 links, this process is interrupted in the stomach because the pH is low but resumes in the small intestine, where salivary amylase resumes and amylase from the pancreas also acts on starch
starch is broken down into smaller shorter chain glucose polymers (disaccharides)
in the small intestine isomaltase and glucoamylase break these down even further so all of the starch is converted to glucose
glucose is absorbed in the small intestine by active uptake

Question 13

disaccharide digestion

Answer 13

sucrose (glucose and fructose) is broken down by sucrase to glucose
lactose (galactose and glucose) is broken down by lactase to glucose
galactose and fructose are broken down in the liver

Question 14

distribution of the lactase persistence phenotype

Answer 14

65% of the world is lactose intolerant
lactase is expressed in infants , but normally this switches off by adulthood, due to exposure in many parts of the world which means it doesn’t not switch off
being unable to digest lactose leads to a lot of digestive problems

Question 15

anaerobic and aerobic glycolysis

Answer 15

always phosphorylated to to glucose-6-phosphate
in the muscle and liver there are storage form of glucose (glycogen) this can be broken down to glucose-1-p which interconvertible to glucose-6-p
in the cytoplasm glucose 6p becomes pyruvate
in aerobic the pyruvate can enter into the mitochondria
in anaerobic pyruvate becomes lactate

Question 16

what are fatty acids

Answer 16

components of fat
tissues store it triacylglycerol (adipose, but also liver and muscle)
double bond causes a kink in a straight chain

Question 17

describe digestion of triacylglycerol

Answer 17

insoluble so it has to be solubilised by bile acids and salts
these are produced in the liver and stored in the gallbladder and then secreted into the small intestine
they are hydrophobic on one side and hydrophilic on the other, they act to bring TAG into solution in the form of micelles where it is acted on by pancreatic lipase to be digested

Question 17

describe chylomicrons

Answer 17

TAG is packaged by the intestinal cells and secreted via the lymphatic system into the blood in the form of chylomicrons
they are the digested and transported form of TAG

Question 18

overview of the digestion and transportation of dietary fat

Answer 18

TAG is solubilised by bile to monoacylglycerol (glycerol with a single fatty acid attached), this is taken up by intestinal enzymes and reassembled to TAG and packaged into chylomicrons
these then circulate the blood and are then hydrolysed by lipoprotein lipase to fatty acids and glycerol, they can then be taken up and oxidised or reconverted to TAG

Question 19

what happens to TAG during starvation and exercise

Answer 19

TAG is broken down to liberate free fatty acids in the plasma, they travel bound to albumin as they are not very soluble, these can be taken up and oxidised to yield energy

Question 20

overview pf protein turnover

Answer 20

proteins in the body are constantly being broken down and resynthesised
when its broken down the constituent amino acids are released into an amino acid pool to resynthesise proteins or drained by removal of amino acids to make the biosynthetic products or for energy production
amino acids can be broken down, amino group is removed and excreted as urea, then the carbon skeleton can be metabolised (completely oxidised to CO2 or can be changed to other circulating intermediates such as glucose or ketone bodies)

Question 21

what is nitrogen balance

Answer 21

the net total of nitrogen in your body
nitrogen balance - excreting the same volume as ingesting
positive nb - synthesising more than excreting, possibly due to growing or being pregnant
negative nb - excreting more than ingesting, occurs during starvation and diseases
nitrogen balance results in a requirement for dietary protein

Question 22

overview of protein digestion

Answer 22

principle enzyme in stomach is pepsin, has a very low ph, it unfolds proteins and denatures them, also makes them more susceptible to proteolytic attack and halts bacterial growth
pancreatic proteases (trypsin, chymotrypsin, elastase, carboxypeptidases and bicarbonate) and peptidases secreted by small intestine also help break down proteins

Question 23

overview of zymogens

Answer 23

trypsinogen is activated by enteropeptidase in the small intestine to become trypsin
trypsin then activates itself, chymotrypsin, elastase and carboxypeptidase
theses are all zymogens which have different specificities (hydrolysed different peptide bonds

Question 24

how are amino acids excreted during protein turnover

Answer 24

transamination (the removal of the amino group) to form amino acid glutamate
that leaves the carbon skeleton of the amino acid which are broken down to C02
the amino group is dealt with by excretion via urea, glutamate is converted to alanine during transport, then glutamate is reformed in the liver

Question 25

how are amino acids metabolically classified

Answer 25

some are broken down to form glucose, very important during starvation, they are used to maintain the plasma glucose concentration
some are converted to ketone bodies
large amino acids are broken into both, part of the backbone form glucose and part to ketones