CFB 6: Getting Nutrients (Biochemistry)

Metabolism focuses on _____ molecules.

Small

Different tissues carry out _________ processes.

Different tissues use (and produce) _________ fuels.

Differences can be mediated by _________ enzymes/isozymes.

Different!

Glucokinase vs. hexokinase

Glucokinase: liver/β cells

Hexokinase: ubiquitous

What are pathways?

Series of enzyme reactions that do the chemistry proteins are capable of

T/F: Synthetic (anabolic) and degradative (catabolic) are simply identical sequences of enzymes working in 2 directions.

False

What pathway steps are regulated?

Ones that are out of equilibrium

T/F: Serine synthesis and degradation follow identical paths.

False

Catalysts change ____, NOT ___________.

Change rate, NOT equilibrium

Regulation (e.g. glycolysis) occurs at steps that are close to/far from equilibrium?

Far from

How can you regulate individual enzymes?

1. Inhibition or stimulation by small molecules

2. Covalent modification - inhibition or activation

3. Regulation of amount of enzyme

4. Compartmental separation

Inhibition or stimulation by small molecules (inc. allosteric) has an _________ effect.

Immediate

Covalent modification is often done by what?

Phosphorylation

Allows signaling control, rapid

Example of compartmental separation

Intracellular (transport of fatty acids into mitochondria for oxidation)

Glucose oxidation hormone

Insulin

Glucose synthesis hormone

Glucagon

Insulin is the hormone of the ________ state.

Well-fed

Glucagon is the hormone of the _______ state.

Starved

Epinephrine is the hormone of _____ ______.

Acute stress

Cortisol is the hormone for ______ ____ _________.

Longer term responses

Protein is how many calories per gram?

4 C/g

Fat is how many calories per gram?

9 C/g

How does blood glucose respond to a carbohydrate meal?

Plasma glucose peaks at about 40 minutes then declines

What is glycemic index?

The ability of a food to raise blood sugar

What is the area under the curve?

Blood glucose

Glycemic index varies for what?

Different carbohydrate foods

Glycemic index affects the size of the _______ response.

Insulin

Factors influencing GI

Sugar content (glucose vs. fructose)

Type of starch (amylose vs. amylopectin)

Physical barriers (bran)

Viscosity of soluble fiber (apple)

Fat and protein content (effects gastric transport)

Acid content (affects gastric transport)

Food processing (rolled oats vs. quick oats)

Cooking (al dente spaghetti)

Carbohydrate digestion starts in the _____.

Mouth

Digestion of what yields maltoses and limit dextrins?

α-Amylase

What bonds does α-Amylase break?

α-1,4 bonds

Does digestion occur in the stomach?

No

Digestion continues in the _________ with what secretions and what disaccharidases?

Intestine

Pancreatic secretions

Membrane-bound disaccharidases

What does cholecystokinin (CCK) do?

Stimulates release of bile and pancreatic enzymes (including amylase)

Food reaching the small intestine stimulates I-cells to produce what?

CCK

What is the action of α-amylase?

Cleaves glucose α1→4 glucose bonds but not glucose α1→6 glucose bonds

Brush border CHO enzymes

Sucrase-isomaltase

Maltase-glucoamylase

Lactase

How do monosaccharides generated at the brush border get into the system?

1. Simple diffusion down a gradient

2. Facilitated diffusion

3. Active transport

When is simple diffusion used to get monosaccharides into the system?

Used for "rare sugars" such as arabinose

Least important

Facilitated diffusion increases _____ of transport down a gradient.

Rates

What is the most common method of monosaccharides generated at the brush border getting into the system?

Facilitated diffusion

Active transport increases transport _____, even against a ________.

Rates, even against a gradient

What does SGLT1 do?

Transports glucose and galactose

Sodium-glucose-linked-transporter-1

What are the 2 types of SGLTs?

Intestinal mucosa

Kidney brush border (SGLT2)

What are the 3 types of facilitative transporters?

GluT4

GluT2

GluT5

GluT4 is responsive to _______.

Insulin

Which GluT transporters are not responsive to insulin?

GluT2

GluT5

Where is GluT2 found?

Liver, pancreas, intestine

Where is GluT5 found and what does it transport?

Small intestine

Transports fructose

The portal circulation carries glucose from where to where?

Intestine to liver

What is the first organ to see elevated carbohydrates after eating?

Liver

T/F: Once in the circulation, glucose still needs to be transported.

True

Liver removes _______ from the circulation.

Glucose

What might you expect from GluT2 deficiency in the liver?

Fanconi-Bickel Syndrome (liver not filtering glucose)

Post-prandial hyperglycemia

What reduces blood sugar?

Insulin

Insulin reduces blood sugar by doing what?

By stimulating uptake into muscle and fat cells

How does insulin stimulate glucose uptake?

Increasing # receptors on plasma membrane

What does SGLT2 in the kidney do?

Prevents loss of glucose to the urine

Humans lack the enzyme to break down _________ sugars found in beans.

Raffinose sugars

What happens if you cannot digest the carb?

Intestinal bacteria metabolize these sugars, giving off hydrogen and carbon dioxide

Lactose intolerance is a deficiency in what?

Lactase

When can lactose intolerance be diagnosed?

Failure to observe glucose increase after lactose challenge

Can observe H2 in the breath

What happens in the gut in lactose intolerance?

Lactose cannot be converted to glucose and galactose

Sources of malabsorption problems

Diet of poorly digestible CHO

Release of pancreatic amylase

Disaccharidases

Absorption by intestinal epithelia

What happens if you cannot release pancreatic amylase?

Pancreatic disease

Cystic fibrosis

What happens if disaccharidases don't work?

Low enzyme levels

-Lactase

-Intestinal illness

Genetic defects

-Sucrose-isomaltase

What happens if absorption by intestinal epithelia is faulty?

Transporter insufficiency

-SGLT1, fructose

Celiac Disease

What are major components of dietary fiber?

Undigested polysaccharides

Your infant is recovering from an intestinal virus. She has abdominal distension after feeding. A deficiency of which enzyme causes the problem?

F

Carbohydrate digestion begins in the mouth with which enzyme?

Amylase

Carbohydrate digestion continues in the small intestine with which enzymes?

Pancreatic amylase

Brush border disaccharidases

-Lactase

-Sucrase-Isomaltase

-Glycoamylase/maltase

-α-dextrinase (isomaltase)

What do bacteria in the colon do?

Digest unabsorbed carbs

Active transport of glucose occurs in which tissue?

Kidney to prevent loss of glucose to the urine

Insulin increases the transport of glucose from the blood into...?

Muscle cells