biochem chapter 14

What is the second stage of energy release?

Small molecules are further degraded into key molecules, especially Acetyl CoA.

What is produced in the third stage of energy release?

ATP is produced from the complete oxidation of Acetyl CoA.

What is the key molecule involved in the second stage?

Acetyl CoA 

What cycle is associated with the complete oxidation of Acetyl CoA?

The Citric acid cycle

What do proteolytic enzymes do in the stomach?

Digest proteins to amino acids

What maintains the pH in the stomach?

A H+-K+ ATPase pump

Which proteolytic enzyme is key in the stomach?

Pepsin

What breaks peptide bonds during digestion?

Proteases

What stimulates the release of secretin?

Low pH of food

What does secretin promote the release of from the pancreas?

NaHCO3

What promotes the release of cholecystokinin (CCK)?

Peptides in food

What does CCK promote the release of from the gallbladder?

Bile salts

What are the initial digestion products in the stomach?

Proteins + HCl + Pepsin → Oligopeptides

What is the role of NaHCO3 in digestion?

Neutralizes stomach acid in the small intestine

What are the components involved in the digestion process?

Proteins, HCl, Pepsin, NaHCO3, Digestive enzymes, CCK

What is the function of bile salts in digestion?

Emulsify fats to aid digestion

What role do proteases play in digestion?

hydrolyze peptide bonds

How do proteases hydrolyze peptide bonds?

by adding water.

What is the chemical process of peptide bond hydrolysis?

Peptide bond hydrolysis involves a peptide, carboxyl component, and amino component.

What are the pH activity levels for pepsin and chymotrypsin?

pepsin: ph 2, chymotrypsin: ph 6

What are zymogens?

Inactive precursors of proteases

How are zymogens activated?

By protease digestion

What is the role of pepsinogen?

It has low level protease activity and can self-activate at low pH

What is the active enzyme of pepsinogen?

Pepsin

What is the active enzyme of chymotrypsinogen?

Chymotrypsin

What is the active enzyme of trypsinogen?

Trypsin

What is the active enzyme of procarboxypeptidase?

Carboxypeptidase

What is the active enzyme of proelastase?

Elastase

What are the advantages of zymogens?

Prevents premature activation of proteases

What activates trypsinogen?

Cleaved by enteropeptidase

What does trypsin do?

Activates other digestive zymogens

Where is trypsinogen made?

In the pancreas

What happens if trypsin is active in the pancreas?

Can lead to digestion of pancreatic tissue

What is the role of enterokinase?

Activates trypsinogen to trypsin

What is trypsin derived from?

Trypsinogen through cleavage

What cleaves peptides into amino acids and di- and tripeptides?

Membrane-bound peptidase

What moves different classes of amino acids and peptides into intestinal cells?

Specific transporters

What enzyme in saliva breaks down polysaccharides?

α-amylase

What bonds does α-amylase cleave?

1-4 bonds only

what does a-glucosidase cleave?

maltotriose, maltose, and other oligosaccharides

What is the main substrate for α-amylase action?

Starch

What enzyme cleaves maltotriose and maltose?

α-glucosidase

What does α-dextrinase cleave?

α-limit dextrin into simple saccharides

Which enzyme digests starch?

α-Amylase

What are the main monosaccharides involved in intestinal transport?

glucose, galactose, fructose

Which transporter is responsible for glucose and galactose transport?

SGLT (sodium-glucose linked transporter)

Which transporter is responsible for fructose transport?

GLUT5

What does GLUT2 do in monosaccharide transport?

Releases monosaccharides into the bloodstream

Where do glucose and galactose get transported from?

From the lumen to the intestinal cell

What is the role of SGLT in carbohydrate transport?

It transports Na+ along with Glucose and Galactose.

What is the role of GLUT5?

It facilitates the transport of Fructose.

What transport protein is responsible for Glucose and Galactose in intestinal cells?

GLUT2.

What is the function of peptidases in the intestinal cell?

They break down peptides into amino acids.

What is the energy content of lipids?

Lipids have a high energy content and are highly reduced.

In what form are most lipids ingested?

Most lipids are ingested as triacylglycerols.

What must lipids be converted to for absorption?

fatty acids

What enhances emulsification in the intestine?

Bile salts

Where are bile salts synthesized?

Liver

What do lipases digest triacylglycerol (TAG) into?

fatty acids and monoacyglycerol (MAG)

What carries digestion products to the plasma membrane?

Micelles

What is reassembled in the intestinal epithelium?

Triacylglycerol (TAG)

How are fatty acids and MAG imported into intestinal cells?

Through fatty-acid-transport proteins (FATP)

What moves fatty acids to the smooth endoplasmic reticulum?

Fatty-acid-binding proteins (FABP)

What is TAG resynthesized into?

Chylomicrons

What binds to membrane-bound lipoprotein lipases?

Chylomicrons

Where is TAG reformed for storage?

In adipose tissue and muscle

What is the fate of TAG in muscle and other tissues?

For oxidation

Where do chylomicrons go after intestinal cells?

To the lymph system and then to blood

What is the role of lipases in the absorption process?

To degrade TAG into FAs and MAG for uptake

What hormones signal satiety in the short term?

CCK and GLP-1

What does leptin report in long-term signaling?

TAG levels

"

• Increases satiety

• Decreases food intake

Decreases body weight

"

How does GLP-1 affect the body?

"

• Increased insulin secretion

• Increased insulin biosynthesis

• Increased β-cell proliferation

• Increased β-cell survival

"

What are the effects of insulin on the pancreas?

They are closely linked

What is the relationship between cell signaling, digestion, and metabolism?

Effects on intestine, brain, and pancreas

What is depicted in the diagram related to GLP-1?

what does a-dextrinase cleave?

a-limit dextrin into simple saccharides