23 Flashcards
What are the main macronutrients contributing to energy production in the body
Carbohydrate, protein and fat
Why are (to a lesser extent) nucueic acidds important?
- protein and nucleic acid components supply body with nitrogen which is important for the biosynthesis of various nitrogen compounds that we need for cellular function
Why are larger compounds broken down
To be absorbed by the body
Main food components and what they’re broken into
After macronutrients are consumes in the diet, where do they pass through?
The GI tract
These smalle dmolecules are used to
Make ATP
Saliva at what ph contains what to start what?
S aliva (neutral pH) contains mucous and amylase which starts the digestion of carbohydrates
Function of stomach - what does it do and what dies it produce
Storage and mixing of food with gastric juices, producing the ‘chyme’ that is slowly released into intestine
Things that are secreted into the stomach (by the stomach?)
secretes acid (0.1 M HCl) =
denaturing
secretes pepsinogen -> pepsin secrete
= protein digestion (protease)
secretes mucous layer (protective)
PH of pancreas
slightly alkaline – around pH 7
Function of pancrease
secretes most of the digestive enzymes including amylase, lipase and several proteases
Function of liver
synthesis of bile salts/acids (stored in gall bladder) important for fat digestion
Function of small intestine
final phase of digestion and absorption
Two main phases of digestion
- Hydrolysis of bonds connecting monomer units in
food macromolecules
Carbohydrate: Glycosidic bonds – starch -> disaccharides
Proteins: Peptide bonds
Fat: Triacylglycerol ester bonds
(This breakdown depends on how fast it can be absorbed into the body)
- Absorption of hydrolysis products from gastrointestinal
tract into body
Digestions of dietary carbohydrates - what percent of energy does it provide - what are some examples
Provides 40-50% of energy intake
Starch (ie. α-amylose, amylopectin)
Simple sugars ie. sucrose, lactose, fructose, glucose (diglucose)
Fibre – such as cellulose (undigestible by most mammals) (don’t have the enzyme to hydrolyse that polymer bond)
Main component of plant starch
Amylopectin
Amylopectin is the main component of…
…plant starch
Amylopectin is a polymer up to ____ _____ Union s
1 million glucose units
Structure of amylopectin
- each bond needs a specific enzyme to be hydrolysed
Maltose is present in…
…honey
Structure of maltose - what kid of polymer..
Disaccharide
C ellobiose and lactose are ________ of one another
stereoisomers
stereoisomers - how Cellobiose and lactose are stereoisomers of one another - what does this mean?
Cellobiose is a repeating disaccharide unit in cellulose
- Mammals do not have an enzyme that can hydrolyse the b(1->4) glycosidic bonds in cellulose
Lactose is present in milk
- Some people do not have the lactase enzyme and are unable to hydrolyse lactose
How do stereoisomers arise
The functional groups in monosaccharides can be in either of two orientations
There is a convention of numbering the carbon atoms
(- any functional groups - like hydroxyl groups can either be pointing out of the carbon or out the other side of the plane of the ring - this influences overall structure (although it has the same chemical make up as another stereoisomer group)
What is sucrose made of
Fructose and glucose
Sucrose is hydrolysed to form
Glucose and fructose
Consumption of ‘high fructose corn syrup’ is increasing - why
Enzyme hydrolysis of ‘corn starch’ to glucose and isomerization to fructose
- easier then other ways of sweetenening?
Starch from plants consists mainly of:
- Amylose (a linear polymer of a(1->4) linked glucose units)
- Amylopectin (a branched polymer of a(1->4) and a(1->6) linked
glucose units)
H ydrolysis of glycogen
Glycogen has a similar branched structure to amylopectin
Glycogen can be present in consumed foods such as liver and muscle
Glycogen is synthesized in animals from glucose and stored in liver and muscle, and then broken down to glucose when required by the body
The breakdown of glycogen stored in liver and muscle cells to glucose requires a ‘debranching enzyme’ (will be discussed further in Prof. Julian Eaton-Rye’s lectures)
Glycogen has a similar branched structure to
Amylopectin
Glycogen can be present in consumed food such as…
… liver and muscle
Glycogen is ____ in animals from _____ and stored in ___ and _____, and then broken down to glucose when required by the body
synthesized
glucose
liver
muscle
The breakdown of glycogen stored in liver and muscle cells to glucose requires a_______
‘debranching enzyme’
Hydrolysis of starch - digestion of starch
(Sequential hydrolysis process)
The enzyme amylase hydrolyses a(1->4) glycosidic bonds
Repeated internal attack yielding smaller and smaller oligosaccharides producing maltose/isomaltose disaccharides as end products
Final digestion at ‘Brush Border’ after amylase digestion, what happens - what enzymes do what cells secrete ? What happens after?
Intestinal epithelial cells secrete …
Maltase/isomaltase
Maltose/isomaltose ——-> 2 glucose
Sucrase
Sucrose ———> fructose + glucose
Lactase
Lactose ———> galactose + glucose
The monosaccharides are now absorbed into the body
Isomaltose and maltose
- different isomers = different enzymes
Overview of dietary carbohydrate processing in the gastrointestinal tract
Lactose interlace - how it occurs - what is causes - how to fix it
L actase enzyme deficiency (genetic basis)
Causes bloating, flatulence and diarrhoea due to fermentation of lactose by intestinal bacteria
Need to avoid lactose in diet
Digestion of dietary protein - what this supplies to the body
Supplies amino acids to make body proteins
Supplies essential amino acids
Source of nitrogen for purines, pyrimidines, haem
Carbon skeletons can be used as fuel (N converted to urea and excreted in urine)
Essential amino acids
Leucine Isoleucine
Lysine Methionine
Threonine Phenylalanine
Tryptophan Valine
(Non-essential are the amino acids we have evolved to have enzymes to break down/synthsystie/ interconvert )
Could be obtained form plant or animal sources
Kwashiorkor - what is it caused by, what does it result in - what is low in the blood and what does that affect
‘Kwashiorkor’ is the result of a deficiency of dietary protein which causes an osmotic imbalance in the gastrointestinal system, causing the abdomen to swell (oedema) due to retention of water
In addition, the level of albumin in the blood is low affecting colloidal osmotic (oncotic) pressure, and also transport of molecules, eg hormones and drugs
How are proteases activated ?
by cleavage of peptides from their structure
All proteases secreted as
All proteases secreted as inactive forms (zymogens or proenzymes)
- this minimises unwanted hydrolysis of body structure
Protein digestion
Involves hydrolysis of specific peptide bonds
Performed by several different proteases
All proteases secreted as inactive forms (zymogens or proenzymes)
All proteases activated by cleavage of peptides from their structure
Protease specificity is determined by
adjacent amino acid side chains in protein substrate
Examples of amino acid side chains that determine a specific protease specificity
Pepsin = aromatic - ie Phe, Tyr
Trypsin = positively charged - ie Lys, Arg
Chymotrypsin = aromatic - ie Phe, Tyr
Whether bond is hydrolysed or not depends on the amino acid side chain
Two stages of protein digestion
Endopeptidases attack peptide bonds within the protein (peptide) polymer
- Examples: pepsin, trypsin, chymotrypsin
Exopeptidases attack peptide bonds at the end of protein (peptide) polymer
- Two types:
- Aminopeptidase
- Carboxypeptidase
Endopeptidases vs Exopeptidase in protein digestion
Endopeptidases attack peptide bonds within the protein (peptide) polymer
Exopeptidases attack peptide bonds at the end of protein (peptide) polymer
How is Pepsinogen activated to pepsin
Pepsinogen, the inactive zymogen (proenzyme) is activated to pepsin following exposure of pepsinogen to HCl in the stomach
In the stomach acidic environment, part of the pepsinogen protein unfolds, which activates the pepsin protease and results in hydrolysis of part of the pepsinogen protein sequence to generate stably activated pepsin protease
- activated pepsin can also directly activate inactive pepsin (causes it to refold and become active)
Protein digestion – sequential hydrolysis by proteases
DIAGRAMS
Enterokinase flow on effects on proteases from pancreas - how appropriate proteases are activated at an appropriate time to carry out their function
Membrane bound in the intestine lumen
- able to hydrolyse part of the trypsinogen protein molecule activating it to active trypsin protease
- active trypsin can active chymotrypsinogen to chymotrypsin
- trypsin can also hydrolyse part of procarboxypeptidase to activate it
