Carbohydrates

Polyhydroxy compounds

aldehydes, ketones, alcohols,, acids and amines

Simply carbohydrates

* used for cellular foods
* either aldehydes or ketones

Simple formula for carbohydrate

Cn(H2O)n

What are the 3 forms of carbohydrates

1. Fischer
2. Haworth
3. Conformational

Haworth structure

* commonly followed
* best option because its between fischer and conformational

Carbohydrates

capable of isomerization on their own of by the action of cellular enzymes

pyran ring

6 membered ring

furan ring

5 membered ring

Probability of simple carbohydrates forming rings in solution

99%

Anomeric carbon

* C1 in a six-membered ring
* Center of the 2 configurational isomers (alpha and beta)
* Is reactive
* Also known are reducing carbon since it donates electrons

Why is the reactive property of a anomeric carbon useful?

determination of glucose concentration in blood and urine

what does the aldehyde of C1 and o-toluidine react to form?

colored covalent complex

What does the reaction between anomeric carbon and proteins form?

forms a permanent bond with the proteins

what is special about mannose?

it can exist as a 5 or six membered ring

For monosachharides, how does the sugar exist?

single ring

For disaccharides, how does the sugar exist?

two sugar units

what are the 3 most common disaccharides?

1. maltose
2. sucrose
3. lactose

Maltose

found in germinating cereals and grains, 2 glucose units held together by an oxygen bridge

Sucrose

fund in cane, beets and carrots, one glucose and one fructose joined by an oxygen bridge

Lactose

found in milk, galactose and glucose joined by an oxygen bridge

are the oxygen bridges the same for each disaccharide?

no, it varies

What type of linkage does maltose have?

alpha(1-4) linkage

What type of linkage does sucrose have?

alpha(1-2) linkage

What type of linkage does lactose have?

beta(1-4) linkage

Where is the anomeric carbon in disaccharides?

present ONLY in the right-hand 6 membered ring

Oligosaccharide

carbs with more than one units

Glycan

number of saccharide rings greater than 10

Polysaccharides

carbs with many sugar units

What are the 2 main functions of polysaccharides/

* storage
* structure

Glycogen

storage form of polysaccharide in animals, very compact molecule due to extensive branching which is desirable for storage

Where is glycogen found in the eye?

corneal epithelial cells and retinal Muller cells

Corneal endothelial cells and photoreceptors and their relationship to glycogen

* utilize glucose at a higher rate
* cannot store glycogen

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Storing is done by epithelial/Muller cells, usage is by endothelial and photoreceptor cells

In metabolism, what is a carbohydrate’s role?

act as fuels for metabolism, constitutes of biological structures

Cellular metabolism

energy within glucose converted into a useful form (ATP)

What are the two types of chemical reactions

* catabolic processes (energy produced)
* anabolic processes (energy consumed)

Are anabolic and catabolic reactions linked?

Yes, anabolic reactions NEED catabolic reactions to happen prior

Anabolic processes

reactions that synthesize cellular components and maintain its functions

ATP

adenosine triphosphate

What is important about phosphoenolpyruvate?

used in catabolic reaction that converts ATP to ADP

What 2 things does ATP connect?

anabolic and catabolic reactions

What are the 3 components of ATP?

adenine, ribose, and 3 phosphate groups

Function of the ribose and adenine components of ATP

* acts as handles to position the molecule at enzyme or protein reactive sites
* facilitates release of its potential energy by breaking outermost phosphate (ADP + Pi)

What can lipids and proteins create by general metabolism?

ATP

What is the most common and immediate source of acetyl-CoA and ATP?

carbohydrates

Why is the use of proteins/lipids to make ATP “bad”?

destructive to tissues when usage becomes excessive

What are examples of the body using proteins/lipids for ATP production?

diabetes mellitus or starvation

what is important about the electron transfer step in kreb’s cycle

an important source for **efficient** ATP production

What part of Krebs cycle occurs in the cytoplasm of the cell?

Up to generation of Acetyl-coA

What part of Kreb’s cycle occurs in the mitochondria?

Beyond Acetyl-coA stage

What enters as glucose 6-phosphate?

glucose and galactose

what enters as fructose 6-phosphate

fructose and mannose

Glycolysis

small amount of ATP is produced in the formation of pyruvate

Oxidative phosphorylation

* involves shuttling of electron-bearing compounds along the mitochondrial, inner membrane


* involves production of substantial quantities of ATP

Electron shuttle

ends at the formation of water (by combining hydrogen and oxygen)

Anaerobic phase of glycolysis

begins when pyruvate is converted to lactate

Glucose-6-phosphate

* converted to glycogen for storage
* converted to pentoses for other metabolic requirements of the cell

what is important about Glucose-6-phosphate

metabolic junction for the continuation of glycolysis, storage or the pentose shunt

What does glucose-6-p undergo to create fructose-6-p?

isomerization

What does fructose-6-p undergo to create fructose 1,6-biphosphate? what mediates this sequence?

phosphorylation, phosphofructokinase

phosphofructokinase

a dominating enzyme that controls the rate of the whole pathway

what does fructose 1,6-biphosphate break down into?

glyceraldehyde 3-phosphate and dihydroxy acetone phosphate

why is the presence of a phosphate group on each fragment (see picture) important?

fragments assure that they will remain in the cytoplasm

Where does glyceraldehyde 3-phosphate acquire its 2nd phosphate group from? What does this process require?

inorganic phosphate, requires NAD+ (coenzyme)

What is the result after glycolysis is completed?

* 2 molecules of ATP consumed
* 4 molecules of ATP formed
* NET GAIN: 2 ATP MOLECULES

Pyruvate

last intermediate of the E-M pathway

Anaerobic metabolism

* only on single reaction beyond E-M pathway involving formation of lactate
* quick means for cells to obtain ATP without O2
* Small yield

Breakdown of stored glycogen

* gain of 3 ATPs anaerobically
* no ATP is required to form glucose-6-phosphate from glycogen

Anaerobic glycolysis

* simple
* can run at a faster rate
* cell can obtain a high-energy supply in a short period of time

What pathway do ocular tissues process glycogen?

anaerobic glycolysis

Problems with hard contact lenses

* metabolic strain on the epithelial cells
* 80% of available glycogen used in just over 8hrs of wear
* significant swelling
* due to increase of lactate
* osmotic strain and constant swelling

What happens to the cornea when oxygen falls below 54mmHg?

corneal swelling could be as much as 20% of the tissue volume

How much corneal swelling can happen overnight?

3% swelling, partial pressure of O2 drops from 155 to 60mmHg

Pyruvate diffuses into mitochondria to do what?

begin the aerobic phase of ATP production

Mitochondria function

* manufacture ATP aerobically
* enzymatic processing of reactions, both of which require a separate inner compartment

Structure of mitochondria

oblong shape and double membrane

structural significance of mitochondria INNER membrane

* impermeable to molecules and ions
* has a large surface area due to cristae
* insoluble electron transferring proteins and ATP synthase

Structural significance of the mitochondrial MATRIX

* contains numerous soluble enzymes
* site for conversion of pyruvate to acetylcholine-coA
* pyruvate dehydrogenase complex

During acetylcholine-coA formation, how many electrons are transferred overall?

2 electrons, from pyruvate → NAD+ → NADH

What are important about the 2 electrons during acetylcholine-coA formation?

electrons are the first source of ATP synthesis in the aerobic pathway

Purpose of Krebs cycle

* to supply electrons for the synthesis of ATP
* help in energy production

How many steps are there in krebs cycle?

9 enzyme catalyzed reactions

Where does krebs cycle occur?

in the mitochondrial matrix

what happens after 1 kreb cycle

* two carbons are lost as CO2
* Carbons are regained as acetyl-coA

What are the most important steps of krebs cycle for deriving energy?

4, 5, 6, 7, and 9

In krebs cycle, what is GTP converted into?

ATP

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(GTP + ADP → ADP + ATP)

Where does NADH and FADH2 travel during kreb’s cycle? what do they do when they reach their destination?

diffuses from the matrix to the inner mitochondrial membrane, they donate their electrons to the electron transferring proteins

Coenzyme Q

shuttles electrons between protein complex I and III, and also between complex I and II

Cytochrome C

shuttles electrons between protein complex III and IV

NADH

carries electrons to protein complex I

FADH2

carries electron to complex II

in oxidative phosphorylation, where do the hydrogen ions flow back through? what does this flow cause?

pores of fifth protein complex, AKA ATP synthase

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release of ATP from ATP synthase

What is the total amount of ATP produced by the aerobic exit of glycolysis

36-38 ATP molecules

what does the pentose shunt pathway do?

* generation of pentoses
* production of fatty acids
* cell detoxification

Why are fatty acids important?

membrane synthesis

Why are pentoses important?

used for synthesis of nucleic acids and nucleotides such as adenosine

why is cell detoxification important?

removal of destructive forms of oxygen such as hydrogen peroxide

In the pentose shunt pathway, can some of the intermediates be recycled?

Yes

What are the functions of the electrons that are inserted into the coenzyme NADP+?

* reductive synthesis of fatty acids
* removal of hydrogen peroxide by a linked redox system

Redox system

help in detoxification, present in ocular tissues

Gluconolactone

hydrolysis to open the ring structure and produce a sugar acid