Enzymes And The Digestive System (UNIT 1) Flashcards Preview

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What are amino acids?

The basic monomer units which combine to make up a polymer called a polypeptide. Polypeptides can be combined to make proteins.



What different groups is an amino acid made out of?

AROUND CENTRAL C ATOM- AMINO GROUP (-NH2) CARBOXYL GROUP (-COOH)- acidic HYDROGEN ATOM (-H) R GROUP- s variety of different chemical groups. Each amino acid has a different R group.


How is a peptide bond formed?

Amino acid monomers combine to make a dipeptide. CONDENSATION REACTION. Combine -OH from carboxyl group of one amino acid and -H from amino group of another. LINKED BY A PEPTIDE BOND BETWEEN CARBON OF ONE AND NITROGEN OF OTHER. BROKEN BY HYDROLYSIS


Describe the primary structure of proteins.

Through series of condensation reactions, may amino acid monomers can be joined together by POLYMERISATION. Resulting chain is called a POLYPEPTIDE. Sequence of amino acids in a polypeptide chain forms PRIMARY STRUCTURE of a protein.


What does the primary structure determine?

Final shape and function of amino acid. 1 change in primary sequence can change structure and stop it from carrying out function.


Describe the secondary structure of proteins.

Linked amino acids have both -NH and -C=O groups on either side of every peptide bond. HYDROGEN of -NH group has +ve charge while O of -C=O has -ve charge . Two groups readily form weak hydrogen bonds. THIS CAUSES LONG POLYPEPTIDE CHAIN TO BE TWISTED INTO 3D shape (alpha helix).


Describe tertiary structure of proteins.

Alpha helices of secondary structure can be twisted and folded more to give a complex, often unique, 3D structure. 3D shape determines how protein functions and allows it to recognise and be recognised by other molecules.


What bonds maintain the tertiary structure of proteins?

DISULFIDE BONDS- fairly strong IONIC BONDS- formed between any carboxyl and amino groups not involved in forming peptide bonds. Weaker than disulfide bonds, easily broken by change in pH. HYDROGEN BONDS- easily broken but lots of them.


Describe the quarternary structure of proteins.

Large proteins often form complex molecules containing a number of individual polypeptide chains that are linked in various ways. Also non-protein groups associated with the molecules.


What is the test for proteins?


Sample in test tube add equal volume of sodium hydroxide

Add a few drops of very dilute copper sulfate solution and mix gently.

PURPLE indicates peptide bond and hence a protein.



What are enzymes?

Enzymes are globular proteins which act as biological catalysts, they increase the rate of reaction with out changing or being used up.


What is activation energy?

The minimum amount of energy needed to start a reaction. Enzymes lower activation energy.


Describe the structure of an enzyme.

Specific 3D shape, result of sequence of amino acids (primary structure). Large but only small section functional- active site.


What is a substrate?

The molecule on which an enzyme acts upon. Fits into active site (COMPLEMENTARY SHAPE). Forms ENZYME-SUBSTRATE COMPLEX.


How is a substrate held to an active site?

By bonds that temporarily form between certain amino acids of the active site and groups on substrate molecule.


Describe the lock and key model. Limitations.

Substrate will only fit the active site of one particular enzyme. Enzymes are specific to the reaction the catalyse. LIMITATION: Enzyme considered a rigid structure but active site can be changed by other molecules binding to the enzyme.


Describe the induced fit model.

Enzyme changes shape slightly to fit profile of substrate. FLEXIBLE. As enzyme changes shape to fit the substrate, the enzyme puts strain on substrate molecule. This distorts a particular bond and consequently lowers the activation energy needed to break the bond.


Describe the effect of temperature on enzyme action.

Increases KINETIC ENERGY of molecules. Molecules move more rapidly and collide with each other more often. Enzyme and substrate come together more often. RATE OF REACTION INCREASES. Rise in temperature also cause hydrogen bonds and other bonds in the enzyme molecule to break - changes shape. At first substrate fits less easily into changed active site. AT SOME POINT, USUALLY AROUND 60 degrees, ENZYME BECOMES SO DISRUPTED THAT IT NO LONGER WORKS. DENATURED. (PERMANENT)


Describe the effect of pH on enzyme action.

Each enzyme has an optimum pH (WORKS FASTEST). Change in pH reduces effectiveness of enzyme and may cause it to denature. - Alters charges on amino acids of active site. Substrate can no longer become attached. DENATURED. -Can cause bonds that maintain enzymes tertiary structure to break. Changes shape of active site, substrate can't fit. DENATURED.


Effect of substrate concentration on enzyme action.

If amount of enzyme is fixed at constant level and substrate slowly added, rate of reaction increases in proportion to the amount of substrate that is added. MORE COLLISIONS. Active site gradually become filled, until the point where all of them are working as fast as they can. RATE OF REACTION AT MAXIMUM. LEVELS OFF.


What are enzyme inhibitors?

Substances which directly or indirectly interfere with the functioning of the active site of an enzyme and so reduce its activity. Some permanent most temporary.


Describe competitive inhibitors.

SIMILAR SHAPE TO SUBSTRATE. Occupy active site of enzyme. Compete with substrate for available active sites.


How does concentration of a competitive inhibitor affect rate of reaction?

Difference between concentration of inhibitor and substrate that determines effect on enzyme activity. SUBSTRATE CONC. INCREASE- effect of inhibitor reduced. When inhibitor leaves, another molecule can take its place. Could be substrate or inhibitor, depending of cons. of each type. EVENTUALLY ALL SUBSTRATE MOLECULES WILL OCCUPY A SITE. BUT THE GREATER THE CONC. OF THE INHIBITOR, THE LONGER IT WILL TAKE.


Describe non-competitive inhibitors.

ATTACH ENZYME AT A SITE OTHER THAN ACTIVE SITE. When attaches to enzyme, the inhibitor alters the shape of the active site in such a way that substrate molecules no longer fit. ENZYME CANNOT FUNCTION. Not competing for same site so increase in substrate concentration does not decrease the effect of the inhibitor.


What is the test for reducing sugars?

BENEDICT'S TEST (e.g. maltose)

Add food sample to test tube (liquid, if not grind in water)

Add equal volume of BENEDICT'S REAGENT

Heat mixture in gently boiling water bath for 5 min.






Blue- No reducing sugar.


What is reduction?

A chemical reaction involving gain of electrons.


What is a reducing sugar?

A sugar that can donate electrons to another chemical.


What is the test for non-reducing sugars?

(e.g. sucrose) Non-reducing sugars do not change colour of Benedict's reagent.

Must first be broken down into its monosaccharide components by hydrolysis.

First do Benedict's test. NO REACTION-

-Add food sample to 2 cm3 of dilute HYDROCHLORIC ACID, place test tube in gently boiling water bath for 5 min.

HCl with hydrolyse any disaccharide present into monosaccharides.

-Slowly add sodium hydrogencarbonate solution to test tube to neutralise HCl.

-Re-test solution with 2 cm3 of Benedict's reagent in a gently boiling water bath for 5 min.

-if non-reducing sugar was present in original sample will now turn orange/brown.


What is the test for starch?

Add sample to test tube.

Add two drop of iodine solution and shake/stir. 

Presence of starch indicated by blue/black coloration.


What monosaccharides form the disaccharides- MALTOSE/SUCROSE/LACTOSE

Maltose- glucose linked to glucose

Sucrose- glucose linked to fructose

Lactose- glucose linked to galactose


How are disaccharides formed?

When monosaccharides join, a molecule of water is removed in a condensation reaction. The bond formed is a GLYCOSIDIC bond. In reverse 2 monosaccharides formed by hydrolysis reaction


How are polysaccharides formed?

Combination of many monosaccharide molecules joined by glycosidic bonds formed by condensation reactions.


What are most polymers made up of?

Carbon, hydrogen, oxygen and nitrogen


What is a monomer?

Individual molecules that make up chains.


What are polymers?

repeating chains of repeating monomer units.


What are monosaccharides?

Sweet tasting, soluble substances that have general formula (CH2O)n. E.g. GLUCOSE C6H12O6


Describe the process of breaking down a large molecule

Enzymes are specific, more than 1 usually needed to completely break down a large molecule.

Typically one breaks down molecule into smaller section then other enzymes break these into their monomers.

These enzymes usually produced in different part of the digestive system.


Describe the process of starch digestion.

1. Food chewed in mouth, breaking it into smaller pieces, giving it a larger surface area.

2. Saliva enters mouth through salivary glands, contains salivary AMYLASE- starts hydrolysing any starch in the food to MALTOSE. Saliva contains salts to keep neutral.

3.Food swallowed and enters stomach, where conditions are acidic. Acid denatures AMYLASE and prevents further hydrolysis of starch.

4.Food passes into small intestine, mixes with secretion from pancreas called PANCREATIC JUICE.

5. P. Juice contains pancreatic AMYLASE, this continues the hydrolysis of remaining starch to maltose. Kept neutral by salts.

6. Muscles in intestinal wall push food along small intestine. Epithelial lining produces enzyme MALTASE. -

Hydrolysis MALTOSE into alpha glucose.


Describe the digestion of sucrose.

Sucrose usually held within cells so must be physically broken down to release (CHEWING). Passes through stomach and into small intestine, epithelial lining produces enzyme SUCRASE which hydrolyses SUCROSE. Produces GLUCOSE AND FRUCTOSE.


Describe digestion of Lactose.

Small intestine, epithelial lining produces LACTASE. LACTASE hydrolyses glycosidic bond to give GLUCOSE and GLACTOSE.


Why are some people lactose intolerant.

Reduction of lactase production is so great from childhood that they produce little or no lactase. Do not produce enough to digest all lactose the consume.


What are the symptoms of lactose intolerance and how are they caused?

Undigested lactose reaches reaches the large intestine, micro-organisms break it down, giving rise to large volume of gas. Results in bloating, nausea, diarrhoea and cramps.


What does the oesophagus do?

carries food from mouth to stomach. Thick muscular wall.


Describe the stomach and its function in digestion.

Muscular sac, inner layer produces enzymes. Role is to store and digest foods. Gland which produces enzymes that digest proteins. Other glands produce mucus which prevents stomach being digested by its own enzymes.


Describe the small intestine and its function in digestion.

Long muscular tube. Food is further digested by enzymes that are produced by its a walls and by glands that pour secretions into it. inner walls folded into villi, large SA. Further increased SA by millions of tiny projection called microvilli on epithelial cells. Absorbs products of digestion into blood stream.


Describe the large intestine and its function in digestion.

Absorbs water. Most comes from secretions of many digestive glands. food within large intestine becomes drier and thicker in consistency and forms faeces.


Describe the rectum and its function in digestion.

Final section of large intestines. Faeces stored here before periodically being removed via the anus in a process called eggestion.


Describe the salivary glands and their function in digestion.

Situated in mouth. Pass secretions via duct in mouth. Contain enzyme amylase, which breaks down starch into maltose.


Describe the pancreas and its function in digestion.

Large gland situated below the stomach. Produces secretion called pancreatic juice. Contains PROTEASES (protein), LIPASE (lipids) and AMYLASE (starch).


Describe physical breakdown.

Large food broken down by means of structures such as teeth. Makes possible to ingest food but also provides larger SA for chemical digestion. food churned by muscles in stomach wall which also physically breaks it up.


Describe chemical digestion.

Breaks down large, insoluble molecules into smaller, soluble ones. Carried out by enzymes. (more than one needed to break down large molecules). Usually one enzyme splits large molecule into sections and these sections are then hydrolysed into smaller molecules by one or more additional enzymes.


Which 3 enzymes are important in chemical digestion?

Carbohydrases- carbohydrates to monosaccharides Lipases- lipid (fatty acids) to glycerol and fatty acids. Proteases- proteins to amino acids.


How are monosaccharides, glycerol, fatty acids and amino acids absorbed? What then happens to them?

By various means from small intestine into the blood. They are carried to different parts of the body and are often built up again into large molecules (not necessarily the same as before). These molecules are incorporated into body tissues and/ or used in processes within the body. This is called ASSIMILATION.