enzymes and digestion for o level and igcse students.pdf

this ppt is about how biological molecules such as enzymes help living organisms absorb food materials in its simplest form.

1. ENZYMES AND
DIGESTION
•Enzyme action; Effect of temperature and pH;
•Nutrients; diet; World food supplies; Human alimentary canal (digestive system);
chemical and mechanical digestion; absorption and assimilation

2. ENZYMES ACTION
▪Catalysts:
–Substance that alters the rate of reaction
–Does not change or gets effected by the end of the process
▪Enzyme:
–Biological catalysts
–Made out of protein
–Alters the rate of reaction without getting changed or effected by the end of the chemical reaction.
▪Substrate:
–Substance on which the enzyme acts is called substrate.
▪Lock and key hypothesis: (5 marks)
–Active sites are depressions or pocketson the
surface of an enzymemolecule.
–Substrate molecule fits into it just like lock and key.
–Enzyme is thelock; substrate is thekey.
–Substrate binds to the active sites of theenzyme forming anenzyme-substrate complex.
–Reaction takes place on active site, converting substrate intoproductmolecules.
–Productmolecule separates, leaving theenzyme moleculeunchanged and free to combinewith more
substratemolecules.

3. EFFECT OF TEMPERATURE AND PH ON ENZYMES
Temperature
▪An enzyme is less active at very low temperature.
▪The more the temperature, thehigherthe enzymeactivity untilthe
optimum temperature is reached.
▪Enzymes works best at optimumtemperature; catalyzes large
number ofsubstrates per second.
▪Temperature raise increases the kinetic energy of enzymeand
substrate; the more the kinetic energy the more the number of
collisions hence increased numberof enzyme-substrate complex.
(37-45)
▪Beyondoptimum temperature theenzyme activity decreases.
▪Increase in temperature increases thevibrationsof enzymes which
breaks the hydrogen bonds, causing it to loose it's shape and active
sites. The enzyme is said to be denatured.
▪The substrate can no longer fit into enzymes active
site and no reaction will occur as the enzyme can no
longer act as a catalyst.
pH
▪Some enzymes works best at neutral pH such as
urease
▪Urease is an enzyme that catalyzes the
hydrolysis of urea forming ammonia and
Carbon dioxide.
▪Some enzymes works best at acidic pH such as
pepsin
▪Pepsin isa stomach enzyme that serves to
digest proteins found in ingested food.
Gastric chief cells secrete pepsin as an inactive
zymogen called pepsinogen. Parietal cells
within the stomach lining secrete hydrochloric
acid that lowers the pH of the stomach. A low
pH (1.5 to 2) activates pepsin.
▪Some enzymes works best at alkaline pH such as
Lipase in pancreas.
▪Lipase isa type of protein made by your
pancreas, an organ located near your
stomach. Lipase helps your body digest fats.
It's normal to have a small amount of lipase in
your blood. But, a high level of lipase can mean
you have pancreatitis, an inflammation of the
pancreas, or another type of pancreas disease.

4. DIET AND DEFICIENCIES

5. A BALANCED DIET
▪A balanced diet consists of all the
food groups in the right proportion.
▪The necessary foodgroups are:
–Carbohydrates
–Proteins
–Lipids/Fats
–Vitamins
–Minerals
–Dietary fiber
–Water

7. CARBOHYDRATES
elements present: carbon, hydrogen, oxygen
▪As a source of energy.
▪Forms supporting structuree.g. cellulose cell wall in plants.
▪To be converted toother organic compoundslikeaminoacids and
fats
▪Formation of nucleic acide.g. DNA
▪Synthesizelubricants
▪Produce nectar in someflowers.
▪Starch >maltose: throughsalivaryamylase.
▪Maltose > glucose: throughmaltase

8. MONOSACCHARIDES
▪Simplest carbohydrates
▪They havegeneral formulaas
(CH
2O)
n.
▪Monosaccharides
arereducing sugars.
▪The test for reducing sugar is
calledBenedict’s test.
▪They aresugars, which taste
sweet, are soluble in water
and are insoluble in non-polar
solvents.
▪Used as a source of energy in
respiration.
▪Important building blocksfor
large complex molecules.
DISACCHARIDES
▪Formed up of 2
monosaccharides.
▪Examples
ofdisaccharidesare,sucro
se,lactoseandmaltose
▪Sucrose is anon-reducing
sugar.
▪Sucrose is the transport
sugar and Lactose is the
sugar found in milk which
an important constituent
of the diet of young
mammals.
POLYSACCHARIDES
▪Polysaccharidesare polymers
formed by combining many
monosaccharide molecules (more
than two) by condensation
reactions.
▪Polysaccharides does not tastes
sweet.
▪Because of enormous molecules,
the majority of polysaccharidesdo
notdissolvein water.
▪Starch, cellulose and glycogen
aresome examples
ofpolysaccharides.
▪Starch is the main storage material
in plants.
▪Glycogen isthe main storage
material inanimals.
▪Cellulose is themajor
componentof cell walls in plants.

9. FATS/LIPIDS
elements present: carbon, hydrogen, oxygen
▪Most fats (lipids) in the body are made up oftriglycerides
▪Their basic unit is1 glycerol molecule chemically bonded to 3 fatty
acid chains
▪The fatty acids vary in size and structure
▪Lipids are divided intofats(solids at room temperature)
andoils(liquids at room temperature)
▪
GLYCEROL

10. PROTEINS
elements present: carbon, hydrogen, oxygen,
nitrogen, sulfur
▪Long chains ofamino acids
▪There are about 20 different amino acids
▪They all contain thesame basic structurebut the‘R’
group is different for each one
▪When amino acids are joined together a protein is
formed
▪The amino acids can be arranged in any order,
resulting in hundreds of thousands of different
proteins
▪Even a small difference in the order of the amino acids
results in a different protein being formed
▪An average amino acid chain contains about 500 units.

11. PROTEIN SHAPE
▪There are thousands of different proteins in the human body and other organisms
▪Many of these proteins aredifferent shapesand the shape often has an important effect on the function of
the protein
▪For example:
–Enzymeshave an area in them known as theactive site- this is important as this is the place where another molecule
fits into the enzyme in order for a reaction to take place
–If theshape of the active site does not match the shape of the moleculethat fits into it, thereaction will not take
place
–Every enzyme has a different shaped active site
–Antibodiesare proteins produced by certain types ofwhite blood cellto attach to antigens on the surface of
pathogens
–Theshape of the antibody must match the shape of the antigenso that it can attach to it and signal it for
destruction
▪Thedifferent sequences of amino acidscause the polypeptide chains tofold in different waysand this
gives rise to the different shapes of proteins
▪In this way every protein has aunique 3-D shapethat enables it to carry out its function

12. AMINO ACID
▪PROTEINS
–Proteins are polymers (and macromolecules) made of monomers calledamino acids
–The sequence, type and number of the amino acids within a protein determines its shape and therefore its function
–Proteins are extremely important in cells because they form all of the following:
▪Enzymes
▪Cell membrane proteins (eg. carrier)
▪Hormones
▪Immunoproteins (eg. immunoglobulins)
▪Transport proteins (eg. haemoglobin)
▪Structural proteins (eg. keratin, collagen)
▪Contractile proteins (eg. Myosin
▪AMINO ACID
▪Amino acids are the monomers of protein
–There are 20 amino acids found in protein common to all living organisms
–The general structure of all amino acids is a central carbon atom bonded to:
▪An amine group – NH2
▪Acarboxylic acidgroup –COOH
▪A hydrogen atom
▪An R group(which is how each amino acid differs and why amino acid properties differ e.g. whether they are acidic or basic or whether they are polar or non-
polar)

13. PEPTIDE BOND
▪In order to form apeptide bonda hydroxyl (-OH) is lost from a carboxylic group of one
amino acid and a hydrogen atom is lost from an amine group of another amino acid
▪The remaining carbon atom (with the double-bonded oxygen) from the first amino
acid bonds to the nitrogen atom of the second amino acid
▪This is acondensationreaction so water is released. The resulting molecule is
adipeptide
▪When many amino acids are bonded together by peptide bonds the molecule formed
is called apolypeptide. A protein may have only one polypeptide chain or it may have
multiple chains interacting with each other
▪Duringhydrolysisreactions polypeptides are broken down to amino acids when the
addition of waterbreaks the peptide bonds

14. CONDENSATION
HYDROLYSIS
AMINO ACID AMINO ACID
DIPEPTIDE
PEPTIDE BOND
(COVALENT)

15. WATER
elements present: hydrogen and oxygen
▪IMPORTANCE AS A SOLVENT:
–Important for all living organisms; many substances
dissolves in it.
▪ROLE WITHIN ORGANISM:
–Dissolved substances can be easily transported around
the organisms – e.g. xylem and phloem in plants and
dissolved food molecules in blood.
–Digested food moleculesare in alimentarycanal but
needsto be moved into the cells. Without water as a
solvent thiswould not be able to happen.
–Toxic waste products such as ureaand
excessivesubstancessuch as salts dissolve in water
and excreteout of the body in form ofurine.
–Water is also an important part of thecytoplasmand
plays a role in ensuringmetabolic reactions can
happenas necessary in cells
–
WATER
MOLECULE

16. FOOD TESTS
▪TEST FOR GLUCOSE
▪TEST FOR STARCH
▪TEST FOR PROTEIN
▪TEST FOR LIPIDS

17. TEST FOR GLUCOSE
(REDUCING SUGAR)
▪AddBenedict's solutioninto
sample solution in test tube
▪Heatat 60 - 70 °c in water
bath for5 minutes
▪Take test tube out of water
bath and observe the color
▪A positive test will show a
color change fromblue to
orange or brick red

18. TEST FOR STARCH
(POLYSACCHARIDE)
▪We can use iodine to test for the presence or absence of starch in a food
sample.
▪Add drops ofiodine solutionto the food sample
▪A positive test will show a color change fromorange-brown to blue-black

19. TEST FOR PROTEIN
▪Add drops ofBiuret
solutionto the food sample
▪A positive test will show a
color change fromblue to
violet / purple

20. TEST FOR LIPIDS
▪Food sample is mixed
with2cm
3
of ethanoland
shaken
▪The ethanol is added to an
equal volume ofcold water
▪A positive test will show
acloudy emulsionforming

21. DIGESTION

22. THE STAGES OF FOOD BREAKDOWN
▪Food taken into the body goes through5 different stagesduring its passage
through thealimentary canal(the gut):
–Ingestion-the taking of substances, e.g. food and drink,into the body through the
mouth
–Mechanical digestion- thebreakdown of foodinto smaller pieceswithout chemical
changeto the food molecules
–Chemical digestion - thebreakdown of large, insoluble molecules into small, soluble
molecules
–Absorption- themovement of small food molecules and ionsthrough the wall of the
intestineinto the blood
–Assimilation- themovement of digested food molecules into the cells of the bodywhere
they are used, becoming part of the cells
–Egestion- the passing out of food that hasnot been digested or absorbed, as faeces,
through the anus

24. STRUCTURE FUNCTION
MOUTH/ SALIVARY GLANDS The mouth where mechanical digestion takes place
•Teeth chew food to break it down into smaller pieces and increase its surface area to volume ratio.
•Amylase enzymesinsalivastarts digesting starch into maltose

Starch Maltose
•Foodis shaped into bolus(ball)by the tongue and is lubricated by salivaso it can be swallowed easily
OESOPHAGUS •Tube that connects mouth to the stomach where the food bolus goes after being swallowed.
•Wave- like contractionsoccurs to push the bolus downwithout relying on gravity
STOMACH •Mechanically digested by churning action.
•Protease enzyme starts digesting protein through chemical digestion
•Hydrochloric acidis present in the stomach which provides optimum pH for the protease enzyme to work and also kills bacteria in the food bolus.
SMALL INTESTINE •Section 1 is called duodenum
•Enzymes in duodenum:
▪Trypsinogen Trypsin
▪Polypeptides Amino Acids
•Section 2 is called Ileum
▪Absorption of digested molecules takes place in this part
▪It is long and lined with villi which is covered with microvilli which increases the surface area to volume ratio of the absorption of the digested food products
such as glucose,fatty acids and glycerol and amino acids.
PANCREAS •Pancreatic juices, intestinal juices and bile is secreted into the small intestine which changes the pH to slightlyalkaline.
▪pHin small intestine is around 8-9
▪Trypsin, pancreatic amylase and pancreatic lipase is released into the small intestine through pancreatic duct.
▪Trypsin converts polypeptide chains into simpleamino acidasthe final product ofprotein digestion.
▪Pancreatic amylasebreaks downmaltose intoglucosewhich is used by the body for energy
▪Excessive glucose is stored in form of small bundles known as glycogen in liver and muscles
▪When the glucose level in the body drops, the glycogen is then broken down into glucose and is used for energy in the body.
Salivary amylase
Enterokinase
Erepsin