Nutritional Pathways Carbs Part 2

Krebs Cycle (Citric Acid Cycle)

second stage of cellular respiration, in which pyruvic acid is broken down into carbon dioxide in a series of energy-extracting reactions

Products of Krebs Cycle

6 NADH, 2 FADH2, 4 CO2, 2 ATP

total ATP production

Glycolysis: 2 ATP, Krebs Cycle: 2 ATP, ETC: 32-34 ATP.

Oxaloacetate

Oxaloacetate is a four carbon molecule that combines with Acetyl CoA in the Krebs Cycle to form citric acid. This citric acid then loses two carbons as carbon dioxide, to form oxaloacetate again, so that the Krebs cycle can begin again.

shuttle systems

enzymatic systems that carry reducing equivalents from cytosolic NADH into mitochondria by an indirect route

What is the glycerol 3-phosphate shuttle associated with?

Brown fat and skeletal muscle

What is the net ATP yield from glucose in the glycerol 3-phosphate shuttle?

30 net ATP

What is the effect of decreased efficiency in the glycerol 3-phosphate shuttle?

Increased heat production

Is the glycerol 3-phosphate shuttle reversible or irreversible?

Irreversible

How many moles of ATP are produced by the glycerol 3-phosphate shuttle?

1.5 moles ATP

What is the Malate-Aspartate Shuttle primarily active in?

Liver, kidney, and heart

Is the Malate-Aspartate Shuttle permeable to the inner mitochondrial membrane?

Yes, it is freely permeable.

What is the reaction that occurs in the cytosol of the Malate-Aspartate Shuttle?

Oxaloacetate is converted to Malate and NADH is converted to NAD+.

What happens in the mitochondrial matrix during the Malate-Aspartate Shuttle?

Malate is converted to Oxaloacetate and NAD+ is converted to NADH.

How many moles of ATP are produced from the electron transport chain (ETC) in the Malate-Aspartate Shuttle?

2.5 moles of ATP

Is the Malate-Aspartate Shuttle reversible?

Yes, it is reversible.

electron transport chain

A sequence of electron carrier molecules (membrane proteins) that shuttle electrons during the redox reactions that release energy used to make ATP.

What is glycogen turnover?

The process of both glycogen synthesis and glycogenolysis. Can operate at same time.

Where is the highest concentration of glycogen synthesis found?

In the hepatocytes of the liver and muscle cells.

What activates glycogen synthase?

Insulin.

What is the key regulatory enzyme in glycogen synthesis?

Glycogen synthase.

What catalyzes glycogen degradation (glycogenolysis)?

The active phosphorylase.

adenosine monophosphate (AMP)

a low-energy compound that results from the removal of two phosphate groups from ATP

Glycogen structure

Branches have alpha(1,6) bonds;

Linkages have alpha(1,4) bonds.

glycogen, liver and muscles

7% liver weight and 1% muscle weight

UDP-glucose

Activated form of glucose for glycogen synthesis.

Glycogenolysis steps

1. One G-1-P molecule is liberated by addition of phosphate from glycogen phosphorylase enzyme

2. G-1-P isomerized to G-6-P which is converted to glucose in the liver or kidney by glucose-6-phosphotase

Phosphorylase b

the dephosphorylated form of glycogen phosphorylase

Phosphorylase B will inhibit what?

Glycogen breakdown. Glycogenolysis is inhibited.

Phosphorylase a

the phosphorylated form of glycogen phosphorylase

G-6-Phosphatase

ONLY IN LUMEN OF ER; G-6-P transported to ER, phosphatase'd the P off, and releases glucose into cytoplasm, leaving cell through GLUT; REVERSES HEXO/GLUCOKINASE

G-6-Phosphatase not in

muscles cells or adipocytes

debranching enzyme

moves a block of oligoglucose from one branch and connects it to the chain using an alpha-1,4 glycosidic link

glycogen phosphorylase

-enzyme that cleaves glucose from the non-reducing end of a glycogen branch by phosphorylating it

-glycogen is more branched (branches occur more frequently) --> more points where enzymes can come in & break down glycogen

*permits rapid release of glucose from glycogen stores

*animals require rapid mobilization of glucose (more than plants)

Covalent regulation of enzymes

when a covalent group, such as a phosphate is added to a protein (to an AA such as Ser, Thr, or Tyr), it creates a negative charge which changes the shape and its activity

allosteric regulation

The binding of a regulatory molecule to a protein at one site that affects the function of the protein at a different site.

What is muscle phosphorylase sensitive to for activation?

Intracellular ligands such as AMP

What inhibits muscle phosphorylase?

Metabolites, ATP, G-6-P, and glucose

What is the function of liver phosphorylase?

Produces glucose for use by other tissues

Is liver phosphorylase sensitive to inhibition by ATP?

No, it is insensitive to inhibition by ATP

Is liver phosphorylase sensitive to inhibition by G-6-P?

No, it is insensitive to inhibition by G-6-P

What regulates liver phosphorylase?

Hormones, including glucagon

reaction 1

glucose to glucose-6-phosphate

reaction 3

phosphofructokinase

reaction 10

PEP to pyruvate

Reaction 1 and 3 bypass

glucose-6-phosphatase and fructose-1,6-bisphosphatase, respectively

remove phosphate groups by hydrolysis

What is oxaloacetate?

An intermediate of the citric acid cycle.

What does oxaloacetate react with to form citrate?

Acetyl-CoA.

Which enzyme catalyzes the reaction between oxaloacetate and acetyl-CoA?

Citrate synthase.

Can oxaloacetate exit the mitochondria?

No.

What is the reaction with PEP carboxylase?

Pyruvate ➔ Oxaloacetate in mitochondria ➔Malate ➔ exit the mitochondria to the cytoplasm➔ oxaloacetate ➔ PEP

Cori Cycle

The removal and recycling of lactic acid by the liver, Liver converts lactic acid to pyruvic acid, Glucose is released to recharge muscle glycogen reserves

glycerol

A three-carbon alcohol to which fatty acids are covalently bonded to make fats and oils.

Glycerol source

Derived from dihydroxyacetone phosphate in glycolysis.

(Fat breakdown in adipose tissue)

pyruvate to oxaloacetate

Pyruvate may be converted to oxaloacetate which can be used for amino acid or glucose biosynthesis

amino acid in TCA cycles

to replenish the intermediates that have exited the mitochondrion in the form of malate or aspartate

TCA cycle

a series of metabolic reactions that break down molecules of acetyl CoA to carbon dioxide and hydrogen atoms

Lactate

a compound produced during the breakdown of glucose in anaerobic metabolism

Hydrolysis of TG

Breakdown of TG into glycerol and fatty acids.

What is produced from the hydrolysis of triacylglycerols stored in adipose tissue?

Fatty acids and glycerol

What do fatty acids provide for muscle and other tissues?

A rich source of energy

How are fatty acids catabolized for energy?

They are converted to acetyl-CoA for entry into the TCA cycle

What happens to glycerol after it is released from adipose tissue?

It travels to the liver for conversion to glucose via gluconeogenesis

Can fatty acids be used to make glucose in humans?

No, because humans lack the necessary enzymes to convert acetyl-CoA to pyruvate or any intermediate along the gluconeogenic pathway

Pentose Phosphate Pathway

A metabolic process that produces NADPH and ribose 5-phosphate for nucleotide synthesis.

NADPH

electron carrier that provides high-energy electrons for photosynthesis

PPP products

NADPH and ribose-5-phosphate

Ribose-5-phosphate

-biosynthetic precursor of nucleotides

-> used in DNA and RNA synthesis

-> Or synthesis of some coenzymes

tissues in high demand for NADPH

mammary glands, adipose tissue, liver, rapidly replicating cells

NADPH and muscles

Limited demand for NADPH and reliance on glucose and fatty acids for E.

CHO intake

45-65% of kcal

CHO sources

-whole grains

-fruits and veggies

-dairy products

-soy products

-sweets

poor CHO sources

meat, eggs, and plant oils

glucose source

fruits and vegetables

mostly from digestion

Galactose source

digested milk

Fructose source

fruit and honey

sucrose source

cane sugar, beet sugar and fruits

Lactose source

milk sugar

maltose source

hydrolysis of starch and seeds

Sugar alcohols are:

sorbitol, mannitol, xylitol

Sugar alcohols are in

nutritive sweeteners

Sugar alcohols are made by

hydrogenation of mono- and disaccharides

What is the AMDR for carbohydrates?

45-65% of energy intake

What is the DRI for carbohydrates for all people over 1 year of age?

> 130g/d

What is one function of carbohydrates in the body?

Energy needed for the nervous system and red blood cells (RBC)

What is one reason carbohydrates are important?

To prevent ketosis

Does the DRI for carbohydrates take exercise into account?

No

What is the general recommendation for added sugars as a percentage of total calories?

Not to exceed 10% of calories

What is the USDA recommendation for added sugars in grams?

Should not exceed 40g (10 teaspoons)

What is the AHA recommendation for added sugars for women?

No more than 100 kcal or 6 teaspoons

What is the AHA recommendation for added sugars for men?

No more than 150 kcal or 9 teaspoons

What is the WHO recommendation for added sugars as a percentage of total calories?

Less than 5%