3.3.3 Digestion and Absorption

Define digestion

The process where relatively large, insoluble biological molecules in food are hydrolysed into smaller, soluble, absorbable molecules

Where is digested molecules absorbed

Across cell membranes into the blood stream

Define digestion

The process where relatively large, insoluble biological molecules in food are hydrolysed into smaller, soluble, absorbable molecules

Where is digested molecules absorbed

Across cell membranes into the blood stream

Why are enzymes important for digestion

they catalyse the hydrolysis

What are the small soluble products of digestion used for

Providing cells with energy or building other molecules for growth, repair and function

What are proteins hydrolysed into

Amino acids

What are carbohydrates hydrolysed into

Simple sugars

What are lipids hydrolysed into

A mixture of glycerol and fatty acids

What does the human digestive system include

Glands, stomachs, small intestine, liver, large intestine

What is the function of the mouth in the digestive system

The mouth breaks food into smaller pieces increasing its Sa:Vol ratio for carbohydrate digestion

What is the function of the stomach

Glandular tissues produces enzymes and stomach acid for protein digestion, food is also churned

Describe the function of the small intestine

Digestion occurs and soluble food molecules are absorbed into the bloodstream

Describe the function of the large intestine

Any remaining water is absorbed and undirected food material is stored in the rectum

Why can enzymes only breakdown a certain substrate

enzymes are substrate specific so only breakdown one thing

What type of enzymes are digestive enzymes

Extracellular enzymes that work outside the cell

Name the three main types of digestive enzymes

Carbohydrase, protease, lipase

Where does digestion of carbohydrates occur

In the mouth and small intestine

What is amylase

A carbohydrase that hydrolyses break down of starch into maltose

What is maltase

Maltose hydrolyses into glucose

Where is amylase made

In the salivary glands, the pancreas and small intestine

Where is maltase made/found

A disaccharide found in cell-surface membranes of the epithelial cells lining the small intestine

Describe the lining of the small intestine

Folded and there are microvilli present

What is the role of microvilli

To increase the surface area substantially, allowing more absorption to occur

Where does protein digestion begin

In the lumen of the stomach

What protease enzyme begins peptide digestion

Endopeptidase

Describe endopeptidases role in protein digestion

Hydrolyses peptide bonds within proteins creating smaller sized protein “chunks”

Where does the food move after endopeptidase

From the stomach to the small intestine

What is endopeptidase secreted with and why

With hydrochloride acid, lowering the pH in stomach

What does pancreatic juice contain

Endopeptidase and exopeptidases

What is the role of pancreatic juice

To neutralise the acidic mixture

Describe exopeptidases role

To hydrolyse the peptide bonds at the ends of polypeptide chains to produce dipeptdes

What is the role of dipeptidase

To hydrolyse dipeptides into amino acids which are released into the cytoplasm

Where are dipeptidase enzymes found

With in the cell surface membranes of of epithelial cells in the small intestine

Describe emulsification

Solid lipids are turned into fatty liquid

What does fatty liquid contain

Fat droplets

What happens when fatty liquid arrives in the small intestine

Bile is secreted

What is bile and where is it made

Contains bile salts which are made i the liver and stored in the gallbladder

What do bile salts do to fatty liquid

It breaks the fatty droplets into smaller one via emulsification

What is the role of emulsification

To help increase the surface area of fatty droplets for digestive enzymes

Where does digestion of lipids occur

In the lumen of the small intestine

What does lipase do

Break down lipids to glycerol and fatty acids

Where is lipase produced and secreted

In the pancreas, secreted into small intestine

What biochemical tests for amlyase

Iodine

What is the purpose of digestion

To break down food into smaller, soluble molecules to be absorbed through the intestinal lining

How are amino acids and monosaccharides absorbed

Via co-transport

What two transport methods are used in co-transport

Facilitated diffusion and active transport

What is produced from lipid digestion

Fatty acids, monoglycerides and glycerol

Define micelles

Monosglycerides and fatty acids associated with with phopsholipids and bile salts

What is the role of micelles in transport

They aid transport to the surface of epithelial cells as monoglycerides and fatty acid are not soluble

What occurs once micelles transport

They break down and add to a pool of fatty acids/monoglycerides

What happens to the pool of fatty acids and monoglycerides

They are dissolved into intestine solution surrounding the epithelial cell

What do the freely dissolved fatty acids and monoglycerides do

Enter epithelial cells by diffusion as they are non-polar

What happens to short fatty acid chains

They move directly into the blood via diffusion

What happens to longer fatty acid chains

They recombine with monoglycerides and glycerol to form triglycerides in the endoplasmic reticulum

What happens to reformed triglycerides

They’re packaged into lipoproteins called chylomicrons

What are chylomicrons

Spherical ‘cases’ made of phopsholipids and lipoproteins that hold non-polar triglycerides from the aqueous environment

Where are chylomicrons transported and how

To the lacteals via exocytosis and eventually enters bloodstream

For starch digestion, as a control, cooked what was chopped up to copy the effect of chewing, suggest a more suitable control and why (2)

Add boiled saliva, as everything will b the same but salivary amylase will denatured

Name the enzyme in the mouth

Amylase

Name the enzymes in the stomach

Pepsin / endopeptidase

Name the enzymes in the small intestine (4)

Endopeptidase, exopeptidase, amylase, lipase

Name the enzymes found in pancreatic juice

Amylase, lipase

Name the enzymes found in microvilli/brush borders of epithelial cells

Maltase and dipeptidase

What reaction does amylase catalyse

Starch to maltose

What reaction does pepsin catalyse

Proteins to polypeptides

What reaction does endopeptidase catalyse

Proteins to polypeptides

What reaction does exopeptidase catalyse

Polypeptides to dipeptides

What reaction does lipase catalyse

Lipids to fatty acid tails and glycerol

What reaction does maltase catalyse

Maltose to glucose

What reaction does dipeptidase catalyse

Dipeptides to amino acids

How do bile salts assist lipid digestion (2)

By emulsifying lipids into smaller fat globules, increase their surface area for digestion by lipase