Carbohydrates I Flashcards
What are the Two Metabolic Pathways
Catabolic Pathways and Anabolic Pathways
What is a Catabolic Pathway
Break down larger molecules into smaller ones
(intermediary metabolites)
– Release large amounts of free energy
– Oxidative – release H atoms – ‘ reducing power’
What is an Anabolic Pathway?
– Synthesise larger important cellular components
from intermediary metabolites
– Use energy released from catabolism (ATP)
– Reductive (i.e. use H released in catabolism
Catabolism Stage 1
what is its purpose
where does it occur
what happens
is energy produced
- Purpose - to convert nutrients to a form that can be taken up into cells.
- Extracellular (GI tract)
- Complex molecules break down to
building block molecules - Short pathways
- Breakage of C-N and C-
O bonds (no C - C) - Building block molecules absorbed from the GI tract into circulation
- No energy produced.
Catabolism Stage 2
what is its purpose
Are there many pathways
where does it occur
what happens
is energy produced
- Purpose - Degradation of building blocks to a small number of organic precursors
- Many pathways – not all in all tissues
- C - C bonds broken
- Intracellular
(cytosolic & mitochondrial) - Oxidative
(require coenzymes which are then reduced, e.g. NAD+ NADH) - Some energy (as ATP) produced
Catabolism Stage 3
what is its purpose
Are there many pathways
where does it occur
what happens
is energy produced
-Mitochondrial
-A single pathway – Tricarboxylic acid (TCA) cycle also know as Krebs cycle
-Oxidative (requires NAD+, FAD)
-Some energy (as ATP) is produced directly
-Acetyl (CH3CO-) converted to 2CO2
-(Also produces precursors for biosynthesis) - precursors are used for metabolic pathways aswell
Catabolism Stage 4
what is its purpose
where does it occur
what happens
is energy produced
-Mitochondrial
-Electron transport and ATP synthesis
-NADH & FAD2H re-oxidised
-O2 required (reduced to H2O)
-Large amounts of energy carrier (ATP) generated
In carbohydrates when can energy be produced without O2
Glycolysis
general formula for Carbohydrates
General formula (CH2O)n
What is an aldehyde
CHO (double bond on the O)
what is a KETO
C=O (has a double bond O but no H)
what is a monosaccharide
single sugar units, (3-9 carbons)
what is a Disaccharide
Disaccharide (2 units)
What is an Oligosaccharide
Oligosaccharide (3 –12 units) e.g. Dextrins
What is a Polysaccharide
Polysaccharide (10 – 1000’s units) glycogen, starch, cellulose
what are the three main dietary monosaccharides
- Glucose
- Fructose
- Galactose
what are the 7 dietary carbohydrates
- Glucose
- Fructose
- Sucrose
- Lactose
- Maltose
- Starch
- Glycogen
what are the three disaccharides and where do you find them
- Sucrose (Table sugar. Glucose-Fructose, a disaccharide)
- Lactose (Milk sugar. Galactose-Glucose, a disaccharide)
- Maltose (Glucose-glucose, disaccharide)
what is starch
(Carbohydrate storage molecule in plants.
Polymer of glucose)
what is glycogen
Carbohydrate storage molecule in animals.
Polymer of Glucose
Highly Branched
What is the major sugar of the blood and what is the conc
Glucose
5 milimolars
What are the two reasons why some cells have an absolute requirement for glucose
Where does this occur
- Due to a lack of mitochondria, thus glycolysis is the only way to produce ATP ( RBC and lens of the eye)
- Due to it being in a low-oxygen environment
Neutrophils are part of the defensive system and often find to self in a low O2 environment, they may have mitochondria but they don’t use them and also the Inner most cells of the kidney Medulla)
What fuel does the brain prefer
What does it use in time if starvation
- CNS (brain) prefers glucose as fuel (approx. 140g/24 hours)
(can use ketone bodies for some energy requirements in times of starvation but needs time to adapt)
Why isnt cellulolse (B,1-4 bonds) digested
Lack of the enzyme essential for breaking the beta-acetal linkages
cellulose (B,1-4) glycosidic bond
Forms linear forms of these polymers.
Well-stabilised internally from hydrogen bonding
alpha (1-4) Bond
More flexibility, allows these molecules to be packed more tightly.
Found in starch and Glycogen
What is primary lactase deficiency?
Absence of lactase persistence allele.
What region has the highest prevalence for primary lactase deficiency
The highest prevalence in Northwest Europe
At what age does Primary Lactase deficiency start
ONLY in adults,
babies have high lactase in the early months however it reduces its ability to digest by 90%
What is Secondary Lactase deficiency
Secondary lactase deficiency is a shortage of lactase caused by a problem in your small intestine
What can cause damage to the small intersitines
- Esessive alchol
- Gastroenteritis
- Coeliac disease
- Crohn’s disease
- Ulcerative colitis
Can Secondary Lactase deficiency be overcome?
Once epithelial cells recover, the deficiency of the secondary lactase is overcome
At what ages does Secondary Lactase deficiency happen
IN BOTH BABIES AND ADULTS
why do you get symptoms from lactose intolerance
When lactose isn’t digested in the small intestines it makes its way to the large intestines.
There, bacteria digest (ferment) it producing gases such as hydrogen and methane
This can change the osmotic environment causing water to be pulled into large intestines causing diarrhoea
what is Congenital lactase deficiency
- Extremely rare, autosomal recessive defect in lactase gene. Cannot digest breast milk.
symptoms of lactose intolerance (5)
Symptoms:
* Bloating/cramps
* Flatulence
* Diarrhoea
* Vomiting
* Rumbling stomach
what are the two steps in Absorption of monosaccharides
Active transport
Passive transport ( simple Diffusion)
how are glucose and galactose absorbed into epithelial cells
Active Transport
what does active transport require
Energy dependant
Sodium dependant
Carrier Protein/ Channel protein
Absorption of monosaccharides, a summary of movement from intestines to cell.
- Active transport (low to high conc) into the intestinal epithelial cells by the sodium-dependant glucose transporter 1 (SGLT1)
- Passive transport (high to low conc), via GLUT 2 into the blood supply
- Transport via the blood supply to target tissues
- Glucose uptake into target cells via facilitated diffusion using transport proteins (GLUT 1- 5) ( high to low conc)
- GLUTS have different tissue distribution and affinities
how does active transport work in the absorption of carbohydrates?
-Sodium is transported into the epithelial cell via diffusion
-Sodium takes glucose along with it from the lumen (happens via SGLT 1)
-Sodium gradient needs to be maintained therefore via active transport 3Na+ is transported out of cell in exchange for 2K+
-this process required ATP converting to ADP
(This Happens in the GLUT-2 )
Two facts about GLUT-2 carrier protein
High Km
Low affinity for glucose
How are GLUTS regulated
They are hormonally regulated (Insulin/glut4)
How many different GLUTs are there
5
Stage 1 Carbohydrate metabolism
Breakdown to building block molecules
what is stage 2 of catabolism of carbohydrates
GLYCOLYSIS - (monosaccharides to pyruvate)
Break down to metabolic materials
release of ‘reducing power’
(NADH) and some ‘energy’
Intracellular, cytosolic
Stage 3 catabolism of carbohydrates
TCA/ Krebs cycle
releases of reducing power
and some energy
AcetylcoA oxidised to CO2
Stage 4 Catabolism of carbohydrates
Oxidative phosphorylation
Conversion of ‘reducing power’ into energy currency ATP
What is it called when the C6 in glucose split into C3
Cleavage
Does glucose get oxidisidised or reduced in glycolysis
There is an oxidation of glucose
What are the Three products of glycolysis
- NADH production (2 per glucose)
- Synthesis of ATP from ADP (net= 2 ATP per glucose)
- Provides biosynthetic precursors for FA, amino acids and nucleotides
What are 6 Features of Glycolysis
- Central pathway of CHO catabolism
- Occurs in all tissues (cytosolic)
- Exergonic, oxidative
- Irreversible pathway
- C6 2C3 (No loss of CO2)
- With one additional enzyme (LDH), is the only pathway that can operate anaerobically
What does HexoKinase (glucokinase in liver) do?
The enzyme responsible for the Change of glucose to Glucose 6-P using ATP
(the phosphorylation of glucose)
What does Phosphofructokinase -1 do?
Phosphofructokinase is an enzyme that controls glycolysis in the body, which is in turn a metabolic pathway necessary for converting glucose into pyruvate
Phase 1 of glycolysis, Reaction 1-3
- Phosphorylation of glucose to glucose-6- phosphate
(G-6-P)
-Makes glucose negatively charged (anionic)
-Prevents passage back across the plasma membrane - Increases the reactivity of glucose to permit subsequent steps
- Phase 1 USES 2 moles ATP per mole glucose
- Reaction 1 and 3 have large negative ∆G values, so are irreversible
- Step 3 - Committing step: first step that commits glucose to metabolism via glycolysis
Phase 2 of glycolysis reaction(4-10)
Reaction 4
* Cleavage of C6 into two C3 units * C3 units interconvertible
(reaction 5)
Reaction 6
* Small amount of reducing power captured (2x NADH)
Reactions 7 and 10 – 4x ATP synthesis
* Transfer Pi to ADP to give ATP * ‘Substrate level
phosphorylation’
Reaction 10
* Large -ve ∆G (exothermic), therefore irreversible
Why are there so many steps (enzymes) in Glycolysis
(4)
Why so many steps/enzymes?
1. Chemistry is easier in small stages
2. Efficient energy conservation
3. Gives versatility
* allows interconnections with other pathways
* allows production of useful intermediates
* allows a part to be used in reverse
4. Allows for fine control
How many enzymes, coenzymes and intermediates are involved in glycolysis
10 enzymes, 5 coenzymes, 9 intermediates
What does the Phosphorylation of glucose to glucose-6- phosphate (G-6-P) do to the glucose
- Makes glucose negatively charged (anionic)
- Prevents passage back across the plasma membrane
- Increases the reactivity of glucose to permit subsequent steps
How much ATP does phase 1 of glycolysis use
Phase 1 USES 2 moles ATP per mole of glucose
Which steps in phase 1 are irreversible for glycolysis and why ?
Reaction 1 and 3 have large negative ∆G values, so are irreversible
What is the committing step in phase 1 glycolysis?
Step 3 - Committing step: first step that commits glucose to metabolism via glycolysis
what happens in reaction 4
of Phase 2 of Glycolysis
Reaction 4
* Cleavage of C6 into two C3 units
* C3 units interconvertible
what happens in reaction 6
of Phase 2 of Glycolysis
Reaction 6
* Small amount of reducing power captured (2x NADH)
(NAD+ becomes NADH)
What happens from reactions 7- 10 in glycolysis
4x ATP synthesis (produced)
* Transfer Pi to ADP to give ATP
* ‘Substrate level
phosphorylation’
What happens in reaction 10 of glycolysis
Reaction 10
* Large -ve ∆G (exothermic), therefore irreversible
IMPORTANT INTERMEITIATES from glycolysis
Fats, Triglycerides
Amino acids - protein sytheisi
Sugars
Heam
Why is lactic acid important in the production of anaerobic glycolysis
When the body has plenty of oxygen, pyruvate is shuttled to an aerobic pathway to be further broken down for more energy. But when oxygen is limited, the body temporarily converts pyruvate into a substance called lactate, which allows glucose breakdown—and thus energy production
Explain how the blood concentraion of lactate is controlled
Lactate can only be metabolized by the conversion to pyruvate. Therefore, blood lactate levels depend on pyruvate metabolism.
Explain the biochemical basis of the clinical conditions of galactosamia
In Galactosaemia, increased activity of the enzyme aldose reductase consumes excess NADPH and in the case of G6PDH deficiency, the production of NADPH is limited (G6PDH is the first enzyme in the pentose phosphate pathway). Insufficient levels of NADPH limit the ability to recycle oxidised glutathione (GSSG) back to its protective reduced form (GSH) leaving the cell susceptible to oxidative damage.
Explain why the pentose phosphate pathway is an important metabolic pathway in some tissues.
- Starts from Glucose-6-Phosphate
- an important source of NADPH
- reducing power for biosynthesis
- maintains GSH levels
- detoxification reactions
Makes C5 sugar ribose used in - Nucleotides
- DNA and RNA
- No ATP made — CO2 made
Describe the clinical condition of glucose 6-phosphate dehydrogenase deficiency and explain the biochemical basis of the signs and symptoms.
This enzyme helps red blood cells work properly.
A lack of this enzyme can cause hemolytic anaemia. This is when the red blood cells break down faster than they are made.
Symptoms during a hemolytic episode may include dark urine, fatigue, paleness, rapid heart rate, shortness of breath, and yellowing of the skin (jaundice).
