Biochem - Digestion and Absorption of Proteins & Carbohydrates

Questions and Answers

Which enzyme is NOT involved in carbohydrate digestion?

Isomaltase

Glucoamylase

Lactase

Dipeptidase (correct)

Which of the following systems primarily facilitates the absorption of monosaccharides into enterocytes?

Facilitated diffusion only

Passive diffusion only

Na+/glucose co-transport and Na+ independent transporter (correct)

Active transport only

What is the primary product of carbohydrate digestion that is generated in the intestinal brush border?

Disaccharidases

Fructose

Galactose (correct)

Maltase

Which of the following statements about the villi in the intestine is FALSE?

They are covered by simple squamous epithelium. Signup and view all the answers

Which mechanism of absorption requires energy and utilizes membrane proteins?

Active transport Signup and view all the answers

The primary method by which peptides enter enterocytes is through what mechanism?

Na+/H+ exchange coupled to H+ gradient Signup and view all the answers

Which statement accurately describes the role of the brush border in the intestine?

It is involved in nutrient absorption and enzymatic digestion. Signup and view all the answers

Which monosaccharide is absorbed by a Na+ independent transporter in the intestinal epithelial cells?

Fructose Signup and view all the answers

Which product of carbohydrate digestion is characterized by being the end product absorbed into the blood?

Free glucose Signup and view all the answers

What is NOT a characteristic of the epithelial cells (enterocytes) in the intestine?

They are primarily responsible for lipid digestion. Signup and view all the answers

Which enzyme specifically cleaves peptide bonds adjacent to basic amino acids?

Trypsin Signup and view all the answers

What type of enzyme is pancreatic alpha-amylase classified as?

Endoglycosidase Signup and view all the answers

Which of the following products is NOT generated during protein digestion?

Oligopeptides Signup and view all the answers

Where does carbohydrate digestion NOT take place in the human body?

Stomach Signup and view all the answers

Which enzyme is secreted by the chief cells of the stomach for protein digestion?

Pepsinogen Signup and view all the answers

What is the pH in the stomach that is optimal for pepsin activity?

2.0 Signup and view all the answers

Which carbohydrate is specifically hydrolyzed by the enzyme lactase?

Lactose Signup and view all the answers

Which pancreatic enzyme is responsible for breaking down tri-peptides?

None of the above Signup and view all the answers

What is the primary function of brush border enzymes in carbohydrate digestion?

Convert disaccharides to monosaccharides Signup and view all the answers

Which of these statements about protein digestion is correct?

Trypsinogen is activated by enteropeptidase Signup and view all the answers

What is the predominant monosaccharide transporter responsible for glucose absorption in the enterocyte?

SGLT1 Signup and view all the answers

Which enzyme is primarily responsible for the breakdown of disaccharides into monosaccharides at the intestinal brush border?

All of the above Signup and view all the answers

Which property distinguishes active transport mechanisms in the absorption of nutrients across the enterocyte membrane?

Utilization of ATP Signup and view all the answers

In addition to glucose, which of the following monosaccharides can be absorbed via passive diffusion in the enterocyte?

Fructose Signup and view all the answers

Which mechanism is primarily responsible for the absorption of peptides in the intestine?

Active transport Signup and view all the answers

What defines the role of microvilli in intestinal epithelial cells?

Increasing surface area for absorption Signup and view all the answers

Which of the following statements about facilitated diffusion is accurate?

It involves specific membrane proteins. Signup and view all the answers

How are amino acids primarily released from enterocytes into the bloodstream?

Exocytosis Signup and view all the answers

What is the primary function of disaccharidases located on the brush border of enterocytes?

Breaking down disaccharides into monosaccharides Signup and view all the answers

Where does the majority of nutrient absorption occur in the gastrointestinal tract?

Small intestine Signup and view all the answers

Which of the following enzymes is an endopeptidase involved in protein digestion?

Chymotrypsin Signup and view all the answers

What type of bonds does pancreatic alpha-amylase specifically cleave in carbohydrates?

a1,4 linkages Signup and view all the answers

Which product of protein digestion is NOT generated in the stomach?

Oligosaccharides Signup and view all the answers

Which enzymes are classified as metalloproteases in protein digestion?

Carboxypeptidase A and B Signup and view all the answers

Which carbohydrate enzyme does NOT primarily act in the small intestine?

Salivary amylase Signup and view all the answers

Which of the following statements about trypsin is true?

It is activated by enteropeptidase. Signup and view all the answers

What is the primary product of carbohydrate digestion in the brush border of the intestine?

Glucose Signup and view all the answers

Which digestive enzyme is responsible for cleaving peptide bonds adjacent to small amino acids?

Elastase Signup and view all the answers

What is the role of brush border enzymes in carbohydrate digestion?

To convert disaccharides into monosaccharides Signup and view all the answers

Which enzyme is NOT listed as anchored to the microvilli in the intestinal brush border?

Sucrase Signup and view all the answers

What is the primary mechanism described for nutrient absorption that does NOT require energy?

Passive diffusion Signup and view all the answers

Which of the following statements correctly describes facilitated diffusion?

It involves the use of membrane proteins. Signup and view all the answers

In the context of nutrient absorption, which means are utilized by enterocytes when energy-dependent mechanisms are employed?

Active transport Signup and view all the answers

Which component is NOT involved in the passive diffusion process?

Energy input Signup and view all the answers

What is the primary mechanism by which peptides are absorbed into enterocytes?

Facilitated diffusion influenced by H+ ions Signup and view all the answers

Which of the following statements is TRUE concerning the absorption of peptides in the enterocyte?

Peptides are absorbed faster than free amino acids. Signup and view all the answers

What role does the Na+/H+ exchanger play in peptide absorption?

It helps maintain the H+ gradient necessary for peptide transport into the enterocyte. Signup and view all the answers

What happens to peptides once they enter the enterocyte?

They are metabolised into free amino acids. Signup and view all the answers

Which factor mainly drives the absorption process of peptides in the enterocyte?

Electrochemical gradient of ions Signup and view all the answers

Which of the following statements about peptide absorption is FALSE?

Peptide absorption is slower compared to free amino acid absorption. Signup and view all the answers

Which enzyme is primarily responsible for digesting polysaccharides in the human body?

α-amylase Signup and view all the answers

Which enzyme specifically targets branch points in oligo- and di-saccharides for digestion?

Isomaltase Signup and view all the answers

What type of enzymes are disaccharidases classified as?

Intestinal enzymes Signup and view all the answers

Which enzyme is responsible for hydrolyzing disaccharides in the intestinal region?

Disaccharidase Signup and view all the answers

In which area does most carbohydrate digestion occur in the human body?

Small intestine Signup and view all the answers

Which site of digestion is NOT involved in carbohydrate digestion?

Stomach Signup and view all the answers

Which enzyme is NOT listed as responsible for breaking down carbohydrates?

Protease Signup and view all the answers

Which of the following products is NOT a direct result of carbohydrate digestion?

Amino acids Signup and view all the answers

Which of the following enzymes is specifically involved in the hydrolysis of trehalose?

Trehalase Signup and view all the answers

Which of the following statements about carbohydrate digestion products is TRUE?

Glucose is a key product of carbohydrate digestion. Signup and view all the answers

Pepsin enzyme, an .......... activated from pepsinogen by HCl. What is the correct term to fill in the blank?

endopeptidase Signup and view all the answers

Pepsin cleaves peptide bonds on the amino side of ........ acids in a highly acidic environment (pH 2.0).

hydrophobic aa Signup and view all the answers

Action of Pancreatic Alpha-Amylase: Endoglycosidase acting on ........, producing maltose, maltotriose, and α-limit dextrins. What type of linkages does it act on?

α1,4 linkages Signup and view all the answers

Which transport mechanism does NOT require sodium ions for the absorption of monosaccharides into the enterocyte?

GLUT-5 Signup and view all the answers

Which monosaccharide transport process uses secondary active transport?

SGLT-1 for Glucose and Galactose Signup and view all the answers

Which of the following correctly describes the exit of monosaccharides from the enterocyte into the bloodstream?

Facilitated diffusion through GLUT-2 Signup and view all the answers

In which scenario is facilitated diffusion of monosaccharides directly dependent on a concentration gradient?

GLUT-5 with Fructose Signup and view all the answers

What is the primary energy source for the sodium-dependent transport processes of monosaccharides into enterocytes?

Sodium gradient maintained by Na⁺/K⁺ ATPase Signup and view all the answers

Which transporter is specifically responsible for the active transport of glucose and galactose into the enterocyte?

SGLT-1 Signup and view all the answers

What is the primary mechanism by which fructose is absorbed into the enterocyte?

Facilitated diffusion through GLUT-5 Signup and view all the answers

What occurs to monosaccharides once they have entered the enterocyte?

They exit the enterocyte via GLUT-2 into the bloodstream. Signup and view all the answers

Which of the following monosaccharides does NOT utilize sodium for its absorption into the enterocyte?

Fructose Signup and view all the answers

What type of transport mechanism does GLUT-2 facilitate for monosaccharides leaving the enterocyte?

Facilitated diffusion Signup and view all the answers

What is the primary function of salivary α-amylase in carbohydrate digestion?

To initiate the breakdown of starches into smaller units Signup and view all the answers

Which statement best describes the role of the stomach in carbohydrate digestion?

It halts carbohydrate digestion due to acidity Signup and view all the answers

During pancreatic digestion, which substance does pancreatic α-amylase primarily act on?

Oligosaccharides Signup and view all the answers

What is the role of brush border enzymes in carbohydrate digestion?

To convert disaccharides into monosaccharides Signup and view all the answers

Which of the following enzymes is NOT typically found on the brush border of the small intestine?

Pancreatic α-amylase Signup and view all the answers

What is the main product generated from the action of maltase?

Glucose Signup and view all the answers

What is the function of trehalase in carbohydrate digestion?

To break down trehalose into glucose molecules Signup and view all the answers

Which environment is primarily responsible for inactivating salivary α-amylase, halting further carbohydrate digestion?

Stomach Signup and view all the answers

Study Notes

learning Outcomes

Ability to describe sources of digestive enzymes for proteins and carbohydrates
Discuss catalytic mechanisms of digestive enzymes for these macromolecules
Understand products arising from protein and carbohydrate digestion
Explain basic mechanisms of nutrient absorption
Describe absorption processes for protein and carbohydrate digestion products

Digestion Overview

Dietary molecules (proteins, fats, carbohydrates) broken down via hydrolytic cleavage by digestive enzymes into smaller units.

Protein Digestion Overview

Main sites: stomach and small intestine.
Proteolytic enzymes secreted into the stomach and released from the pancreas into the small intestine.

Protein Digestion in the Stomach

Key enzyme: Pepsin, an endopeptidase activated from pepsinogen by HCl realesd bu chife cells.
Pepsin cleaves peptide bonds on the amino side of hydrophobic amino acids in a highly acidic environment (pH 2.0).

Protein Digestion in the Small Intestine

Pancreatic enzymes secreted as zymogens:
- Trypsinogen → Trypsin (activated by enteropeptidase)
- Chymotrypsinogen → Chymotrypsin
- Proelastase → Elastase
- Procarboxypeptidase → Carboxypeptidase

Pancreatic Enzyme Types and Mechanisms

Trypsin: Endopeptidase targeting basic amino acids.
Chymotrypsin: Serine protease targeting hydrophobic amino acids.
Elastase: Targets small amino acids.
Carboxypeptidase A & B: Metalloproteases cleaving C-terminus of hydrophobic or basic amino acids respectively.

Products of Protein Digestion

Resulting products: amino acids, di-peptides, tri-peptides, and tetra-peptides.
Cleaved by peptidases before absorption.

Carbohydrate Digestion Overview

Begins in the mouth with no digestion in the stomach.
Key sites: mouth and small intestine.

Carbohydrate Digestion in the Mouth

Sources: starch, lactose, sucrose, trehalose, cellulose.
Mechanical digestion through chewing; chemical digestion via salivary amylase.
Salivary amylase hydrolyzes starch into maltose and dextrins, with ~5% breakdown occurring in the mouth.

Small Intestine Carbohydrate Digestive Enzymes

Enzymes involved: pancreatic α-amylase and Isomaltase (α-(1,6) glucosidase) and brush border enzymes

Action of Pancreatic Alpha-Amylase

Endoglycosidase acting on α1,4 linkages, producing maltose, maltotriose, and α-limit dextrins.
Not effective on α1,6 linkages.

Action of Brush Border Carbohydrate Enzymes These enzymes are located in the brush border of the small intestine, playing a key role in the final stage of carbohydrate

Maltase: Maltose → Glucose + Glucose.
Sucrase: Sucrose → Glucose + Fructose.
Lactase: Lactose → Galactose + Glucose.
Trehalase: Trehalose → Glucose + Glucose.

Carbohydrate Digestion Summary

Sites of digestion: Mouth and intestinal brush border.
Products generated include maltose, maltotriose, glucose, galactose, and fructose.
Enzymes involved: (Gluco)amylase, isomaltase, sucrase, lactase, trehalase.

Mechanisms of Absorption

Transportation of digested products across epithelial membranes, primarily in the small intestine.
Type of absorption: passive diffusion, facilitated diffusion, and active transport.

The Unit of Absorption

Villi covered by simple columnar epithelium.
Brush border increases surface area for absorption significantly.

Epithelial Cells in the Intestine

Enterocytes are the primary absorptive cells with microvilli that anchor digestive enzymes.

Transport of Nutrients

Proteins absorbed as peptides; rapid absorption compared to free amino acids.
Monosaccharides absorbed via passive diffusion and specific transporters (e.g., SGLT1, GLUT5).

Summary

Macromolecules are degraded into smaller units by various enzymes.
Nutrient absorption occurs via diffusion and transport proteins through the enterocyte membrane.

Enzymes Anchored to Microvilli

Brush border of the intestine has an extensive surface area of 200 m², roughly equivalent to half of a FIBA basketball court.
Enzymes with catalytic domains that extend into the intestinal lumen include:
- Aminopeptidase: Cleaves amino acids from the amino end of peptides.
- Endopeptidase: Breaks peptide bonds within the protein chain.
- Carboxypeptidase: Removes amino acids from the carboxyl end of peptides.
- Dipeptidase: Hydrolyzes dipeptides into individual amino acids.
- Disaccharidases: Break down disaccharides into monosaccharides.
- Oligosaccharidases: Hydrolyze oligosaccharides into simpler sugars.

Absorption Mechanisms

Passive Diffusion:
- Occurs spontaneously along a concentration gradient without energy expenditure.
Facilitated Diffusion:
- Utilizes specific membrane proteins located in enterocytes to assist in the movement of substances across the membrane.
Active Transport:
- Relies on energy to transport substances against their concentration gradient using membrane proteins found in enterocytes.

Peptide Absorption Mechanism

Majority of protein absorption occurs in peptide form, facilitating efficient digestion.
Peptide absorption rate is faster compared to the absorption of free amino acids.
The peptide transport process is coupled with the movement of hydrogen (H+) ions, leveraging an electrochemical gradient.
A Na+/H+ exchanger plays a crucial role in maintaining the H+ gradient by extruding H+ ions from the enterocyte while importing sodium (Na+) ions.
Inside the enterocyte, peptides are metabolised into free amino acids, which are the true form that enters the bloodstream.
Only free amino acids are transported from the enterocyte into the blood circulatory system, ensuring body protein needs are met.

Overview of Carbohydrate Digestion

Carbohydrate digestion starts in the mouth and proceeds through the gastrointestinal tract, with final digestion and absorption occurring in the small intestine.

Salivary Digestion

Enzyme: Salivary α-amylase (ptyalin).
Function: Initiates breakdown of starches (amylose and amylopectin) into smaller oligosaccharides, mainly maltose and dextrins.
Location: Takes place in the mouth.

Gastric Digestion

Enzyme: No significant enzymes for carbohydrate digestion are active in the stomach.
Function: Carbohydrate digestion halts due to the acidic environment that inactivates salivary α-amylase; the stomach aids in mixing and churning food.

Pancreatic Digestion

Enzyme: Pancreatic α-amylase.
Function: Continues starch digestion in the small intestine by breaking down oligosaccharides into disaccharides and trisaccharides.
Location: Occurs in the small intestine.

Brush Border Enzymes

Location: Found on the microvilli of enterocytes in the small intestine.
Enzymes and Functions:
- Maltase: Digests maltose into two glucose molecules.
- Sucrase: Breaks sucrose down into glucose and fructose.
- Lactase: Converts lactose into glucose and galactose.
- Trehalase: Splits trehalose into two glucose molecules.

Transport Mechanisms of Monosaccharides

Monosaccharides primarily include glucose, fructose, and galactose, absorbed in the small intestine.
The transport of these sugars occurs through enterocytes, specialized intestinal absorptive cells.

Transport into the Enterocyte

SGLT-1 (Sodium-Glucose Linked Transporter 1):
- Facilitates secondary active transport for glucose and galactose.
- Transport is coupled with sodium (Na⁺) ions.
- Utilizes the energy from the sodium gradient maintained by the sodium-potassium pump (Na⁺/K⁺ ATPase).
GLUT-5 (Glucose Transporter 5):
- Involved in the transport of fructose through facilitated diffusion.
- Unlike SGLT-1, fructose transport does not rely on sodium.

Transport Out of the Enterocyte

GLUT-2 (Glucose Transporter 2):
- Enables the exit of all three monosaccharides (glucose, galactose, fructose) from enterocytes into the bloodstream.
- Operates through facilitated diffusion, transferring sugars from the cell to the blood.

Summary of Key Transporters

SGLT-1: Active sodium-dependent transport of glucose and galactose into enterocytes.
GLUT-5: Facilitated diffusion mechanism for fructose entry into enterocytes.
GLUT-2: Facilitated diffusion process for returning glucose, galactose, and fructose to the bloodstream.

Importance of Transport Processes

The outlined transport mechanisms ensure efficient absorption of dietary sugars after enzymatic digestion, crucial for maintaining energy balance in the body.

Transport Mechanisms of Monosaccharides

Monosaccharides primarily include glucose, fructose, and galactose, absorbed in the small intestine.
The transport of these sugars occurs through enterocytes, specialized intestinal absorptive cells.

Transport into the Enterocyte

SGLT-1 (Sodium-Glucose Linked Transporter 1):
- Facilitates secondary active transport for glucose and galactose.
- Transport is coupled with sodium (Na⁺) ions.
- Utilizes the energy from the sodium gradient maintained by the sodium-potassium pump (Na⁺/K⁺ ATPase).
GLUT-5 (Glucose Transporter 5):
- Involved in the transport of fructose through facilitated diffusion.
- Unlike SGLT-1, fructose transport does not rely on sodium.

Transport Out of the Enterocyte

GLUT-2 (Glucose Transporter 2):
- Enables the exit of all three monosaccharides (glucose, galactose, fructose) from enterocytes into the bloodstream.
- Operates through facilitated diffusion, transferring sugars from the cell to the blood.

Summary of Key Transporters

SGLT-1: Active sodium-dependent transport of glucose and galactose into enterocytes.
GLUT-5: Facilitated diffusion mechanism for fructose entry into enterocytes.
GLUT-2: Facilitated diffusion process for returning glucose, galactose, and fructose to the bloodstream.

Importance of Transport Processes

The outlined transport mechanisms ensure efficient absorption of dietary sugars after enzymatic digestion, crucial for maintaining energy balance in the body.

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Description

This quiz covers the digestion and absorption processes for proteins and carbohydrates in the human body, focusing on the biochemical mechanisms involved. Students will explore the sources of digestive enzymes and their roles in catalyzing these processes. Assess your understanding of gastrointestinal functions essential for health.