Transcript Ch.1: Transformation of Food into Nutrients

Ch.1: Transformation of Food into
Nutrients ;Digestive System
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What does your food include ?????
Inorganic
Water
Organic
Salts
Vitamins
Bases Acids
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Macromolecules
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Carbohydrates
Lipids
Proteins
Nucleic Acids
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 Some molecules are called macromolecules because of their
large size.
 Usually consist of many repeating units.
 Resulting molecule is a polymer (many parts).
 Repeating units are called monomers.
 Some Examples:
Category
Example
Subunit
Carbohydrates
Polysaccharide
Monosaccahrides
Lipids
Fat
Fatty acids + glycerol
Proteins
Polypeptide
Amino Acids
Nucleic Acids
DNA, RNA
Nucleotides
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Monomers
• Smaller units
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Polymers
• Linked up monomers
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Synthesis & Degradation
 Synthesis Reactions (Dehydration‐Removal of water
molecule)
– Used to connect monomers together to make polymers
– Example: Polymerization of glucose monomers to make
starch
 Degradation Reactions (Hydrolysis‐Addition of water
molecule)
– Used to disassemble polymers into monomer parts
– Digestion of starch into glucose monomers
 Specific enzymes required for each reaction
– Accelerate reaction
– Are not used in the reaction
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Synthesis and Degradation of Maltose,
a Disaccharide
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Four Classes of Organic Macromolecules:
1 ‐ Carbohydrates
 Monosaccharides:
– Single sugar molecule
– Glucose, ribose, deoxyribose
 Disaccharides:
– Contain two monosaccharides joined during dehydration
reaction
– Sucrose
 Polysaccharides:
– Polymers of monosaccharides
– Starch, cellulose, chitin
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Carbohydrates:
Monosaccharides
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Single sugar molecules
Quite soluble and sweet to taste
Examples:
• Glucose (blood), fructose (fruit) and galactose
 Hexoses ‐ Six carbon atoms
 Isomers of C6H12O6
• Ribose and deoxyribose (in nucleotides)
 Pentoses - Five carbon atoms
 C5H10O5 & C5H10O4
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Carbohydrates :
Disaccharides
 Contain two monosaccharides joined by dehydration reaction.
 Soluble and sweet to taste.
 Examples:
• Sucrose
– Table sugar, maple sugar
– One glucose and one fructose joined by
dehydration
• Maltose
– Malt sugar
– Two glucoses joined by dehydration
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Carbohydrates :
Polysaccharides
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Polymers of glucose (monosaccharide)
Low solubility; not sweet to taste
Used for short‐term energy storage
Examples
– Starch (plant polysaccharide) as in potatoes &
corn
– Glycogen (animal polysaccharide) stored in
animal’s liver & muscles
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Starch
Glucose
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Polysaccharides
 More polysaccharide examples
• Cellulose
Structural element for plants
Main component of wood and many natural fibers
Indigestible by most animals
• Chitin
Very resistant to wear and digestion
Arthropod exoskeletons, cell walls of fungi
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Four Classes of Organics:
2 ‐ Lipids
 Insoluble in water
 Long chains of repeating CH2 units
 Renders molecule nonpolar
 Types of Lipids:
Type
Organismal Uses
Human Uses
Fats
Long-term energy storage &
thermal insulation in animals
Butter, lard
Oils
Long-term energy storage in
plants and their seeds
Cooking oils
Phospholipids
Component of plasma
membrane
Non-stick pan spray
Steroids
Component of plasma
membrane; hormones
Medicines
Waxes
Wear resistance; retain water
Candles, polishes
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Types of Lipids: Triglycerides
 Triglycerides (Fats)
 Long‐term energy storage
 Backbone of one glycerol molecule
o Three‐carbon alcohol
o Each has an OH‐ group
 Three fatty acids attached to each glycerol molecule
 Long hydrocarbon chain
o Saturated ‐ no double bonds between carbons
o Unsaturated ‐ 1 or more double bonds between
carbons
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Types of Lipids
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Dehydration Synthesis of Triglyceride from
Glycerol and Three Fatty Acids
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Types of lipids: Phospholipids
 Derived from triglycerides
- Glycerol backbone
- Two fatty acids attached instead of three
- Third fatty acid replaced by phosphate group
o The fatty acids are nonpolar and hydrophobic
o The phosphate group is polar and hydrophilic
 Molecules self arrange when placed in water
- Polar phosphate “heads” next to water
- Nonpolar fatty acid “tails” overlap and exclude water
- Spontaneously form double layer & a sphere
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Phospholipids Form Membranes
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Four Classes of Organics:
3 ‐Proteins
 Functions:
 Support – Collagen
 Enzymes –Almost all enzymes are proteins
 Transport – Hemoglobin; membrane proteins
 Defense – Antibodies
 Hormones –Many hormones; insulin
 Motion –Muscle proteins, microtubules
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Amino Acids
 Proteins are polymers of amino acids.
 Each amino acid has a central carbon atom (the alpha carbon) to
which are attached:
- a hydrogen atom,
- an amino group –NH2,
- a carboxylic acid group –COOH
- one of 20 different types of – R groups
 There are 20 different amino acids that make up proteins.
 All of them have basically the same structure except for what
occurs at the placeholder R.
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20 Amino Acids
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The Polypeptide Backbone
• Amino acids joined together end‐to‐end
– COOH of one AA covalently bonds to the NH2 of the next AA
– Special name for this bond ‐ Peptide Bond
• Two AAs bonded together – Dipeptide
• Three AAs bonded together – Tripeptide
• Many AAs bonded together – Polypeptide
– Characteristics of a protein determined by composition and sequence
of AA’s
– Virtually unlimited number of proteins
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Synthesis and Degradation of a Peptide
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What does your digestive
system look like?
The tube starts
here:
And although there
are a few twists and
turns along the
way…
It comes out here:
Anything that goes in
the top hole (mouth)
does not become
part of the body until
it is broken down
then absorbed though
a series of specialized
structures.
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What does the digestive system do?
• INGESTION:
– Eating or taking in the food
• DIGESTION:
– Mechanical vs. chemical digestion
• Mechanical is breaking the food into smaller pieces
• Chemical is using enzymes and chemical reactions to break apart the
molecule
• ABSORPTION:
– Moving the broken down food into the blood or the lymph to be
carried around the body
• ELIMINATION:
– Getting rid of anything that you can’t digest
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Label the Digestive System
Mouth
Tongue
Salivary glands
Oral cavity
Pharynx
Esophagus
Stomach
Pyloric sphincter
Liver
Gall-bladder
Pancreas
Small intestine
Large intestine
Anus
Rectum
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Mouth
• The part where digestion starts
• Tongue – moves around the food and forms a
bolus (a ball of food)
• Contains the digestive juice saliva that is produced by the
salivary glands.
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• What’s in saliva and what does it do?
• Water
– Makes food soft
• Mucus
– Helps food slide down the esophagus
• Bicarbonate ions
– neutralize acid produced by bacteria (helps
prevent tooth decay)
• Salivary amylase
– breaks down starch in the presence of water
– Starch  maltose (a disaccharide of glucose)
How much saliva do you produce in a day?
About 1-2 litres!
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Traveling to the stomach…
• Esophagus
– Tube from pharynx to stomach
– It has:
• Mucus membranes
– Helps the food slide down
• Muscle
– Pushes the food down the tube
• Food moves down by peristalsis
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Reaching the stomach…
• Bolus arrives at the cardiac sphincter
– This is the “door” at the top of the stomach
– Made of muscle
• What is heartburn and what causes it?
• Opening of the cardiac sphincter allowing food (soaked
in stomach acid) to enter the esophagus.
http://www.youtube.com/watch?v=1ZIK6Ua20JA
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The Stomach
• How big is your stomach?
– About 1.5 to 2L in an adult human (300L in a cow!)
This is a
rabbit
stomach
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The Stomach
• J-shaped organ
• Three layers of muscle
– Mix up and break up the food
• Gastric glands make gastric juice
• Gastric juice has:
– Pepsinogen + Hydrochloric acid  Pepsin
• PEPSIN
• an enzyme  it breaks down proteins into peptides
(small protein sections)
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Within the walls of the stomach…
Pepsinogen
Pepsin
HCl
(Activates more
Pepsinogen)
Gastric
gland
Mucus cell (shown in red)
Parietal Cell
Peptic cell
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Why doesn’t the stomach digest itself?
• HCl could eat through the
stomach
 Stopped by the mucus layer
• Pepsin could digest protein in
the stomach cells
 Pepsin is only made when
pepsinogen mixes with HCl
 Stopped by the mucus layer
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When things go wrong…
• Bacterial infections
– Cells can’t make mucus
– Can cause ulcers and stomach cancer
http://www.youtube.com/watch?v=1ZIK6Ua20JA&feature=channel_page
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• How long does food stay in your
stomach?
– 2 - 6 hours
• Chyme = liquid food that leaves your stomach
• Enters the small intestine
 controlled by the PYLORIC SPHINCTER
 “Door” of muscle at the bottom of the stomach
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Small intestine
• Most of digestion and absorption of nutrients occur
here
• How long is your small intestine?
About 6m (20 feet!)
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Small intestine zones
• 3 Zones:
– Duodenum, Jejunum, Ilium
• First 25 cm is the duodenum
• 3 helping organs secrete liquids to the
duodenum:
– 1. Liver
– 2. Pancreas
– 3. Gall Bladder
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How it all fits together…
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Liver
• produces bile (up to 1.5L per day!), stored in the
Gall Bladder
– a thick green liquid
– breaks fat into droplets
• What kind of digestion does bile perform?
– Mechanical or Chemical?
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The Pancreas
• Connected to the duodenum by a duct
• Pancreatic juice has:
– Sodium bicarbonate
 neutralizes the acidic chyme
– Enzymes to further break down food
• Pancreatic amylase
Starch  maltose
• Trypsin
Protein  peptides
• Lipase
Fats  glycerol and 3 fatty acids
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Fats break down to molecular level!
Lipase
Fatty Acid
Glycerol
Fatty Acid
Fatty Acid
Fat
Fatty Acids
and Glycerol
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Intestinal Glands
• Cells lining the small intestine provide the rest
of the enzymes we need
– Peptidases break down proteins
– Maltase breaks down maltose
• Other disaccharides are also broken down, e.g. lactase
breaks down lactose
– Nucleosidases breaks down nucleotides
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Digestive Enzymes from the Interstitial
glands
Maltase
Glucose
Maltose
Peptidase
Peptide
Amino
Acids
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Inside the small intestine
• Large folds line
the intestine
• Villi stick out
from the folds
• Microvilli stick
out from the
villi
~600m2= LOTS of surface
(size of a
baseball
diamond)
area
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The Villi
Outer wall
Pathway
for Food
Inner wall
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Villi
• Each villus has a very
thin layer of cells
around it (epithelium)
• A lymphatic vessel
called a lacteal is at the
centre
• Blood capillaries
surround the lacteal
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Absorbing nutrients
• Fatty acids and glycerol are
absorbed  recombine into fat
molecules in the epithelial cells
• Fats then move into the lacteal
and enter the Lymphatic System
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Absorbing nutrients
• sugars and amino acids enter
the blood
How long is
“food” here?
Up to 4 hours
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A close up look at villi
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Large Intestine
• Consists of the colon, the rectum and the
opening at the end, the anus.
• Colon has 3 parts
– ascending
– transverse
– descending
• How long is it?
– About 1.5m long (about 5 feet)
– Last 20 cm is the rectum
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Humans have a
short caecum
(blind pouch) at
the start of the
large intestine.
The appendix is a
vestigial organ
(not needed).
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What does the large intestine do?
• Reapsorption of water
• Absorption of certain vitamins
• Also contains: bile pigments, heavy metals,
and billions of E. coli (providing colour and odour)
• What do E. coli do for you?
– break down some indigestible food
– produce some vitamins, amino acids, and other
growth factors
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