2. Enzymes and the Digestive System Flashcards

Question

What are the properties of fibrous proteins?

Answer 1

⋆ Structural proteins e.g. collagen ⋆ Polypeptide strands tightly wrapped around one another ⋆ Chains linked by cross-bridges so form very stable molecules ⋆ Suitable as structural proteins because of their cross-linking, parallel layers that move over one another, external R-groups that are non-polar which makes them insoluble

Answer 2

⋆ The structure of collagen: PS: unbranched polypeptide chain SS: tightly wound polypeptide chain TS: chain twisted into a second helix QS: three polypeptide chains twisted together as individual fibres then wound together into a rope shape ⋆ Found in tendon which link muscles to bones ⋆ The point where one collagen molecule ends and the next begins is spread out so they are not all in the same position, which means breakage is not so much of a problem

Answer 3

⋆ Enzymes ⋆ Carry out metabolic functions ⋆ Circular shapes, soluble in water

Answer 4

``` ⋆ Carrier proteins ⋆ Antibodies ⋆ Structural proteins ⋆ Hormones ⋆ Enzymes ⋆ Transport proteins ⋆ Contractile proteins ```

Answer 5

⋆ Globular proteins that act as catalysts ⋆ Alter the rate of a reaction by providing an alternative reaction pathway with a lower activation energy without being used up themselves ⋆ Effective in small amounts and can be reused

Answer 6

⋆ Only a small region of the large protein is functional ⋆ This is known as the active site and is made up of a small number of amino acids ⋆ The active site forms a small, hollow depression within the large enzyme molecule

Answer 7

⋆ The molecule acting on the enzyme is called the substrate ⋆ The substrate is held in place within the active site by bonds that temporarily form between certain amino acids of the active site and groups on the substrate molecule ⋆ The enzyme-substrate complex is created ⋆ Products of the reaction are released from the surface of the enzyme

Answer 8

⋆ Like a lock and key, a substrate will only fit the active site of a particular enzyme ⋆ Enzymes are specific to the reactions they catalyse ⋆ One limitation of this model is that the enzyme, like lock, is considered a rigid structure ⋆ Scientists observed that other molecules could bind to enzymes at sites other than the active site ⋆ This altered the activity of the enzyme ⋆ The other binding molecules therefore alter the enzyme’s shape ⋆ It has a flexible, not rigid, structure

Answer 9

⋆ The enzyme has a certain general shape, but it alters in the presence of the substrate ⋆ As it changes its shape, the enzyme puts a strain on the substrate molecule which distorts a particular bond and consequently lowers the activation energy needed to break the bond

Answer 10

⋆ Rise in temperature increases the kinetic energy of molecules ⋆ Molecules move around more rapidly and collide with each other more often ⋆ This means that the enzyme and substrate molecules come together more often in a given time, so the rate of reaction increases ⋆ After temperatures of around 45 degrees in humans, the hydrogen and other bonds in the molecule begin to break ⋆ This results in the shape of the active site changing as well as the site of the overall protein ⋆ This slows down the rate of reaction as the substrate is less able to bind to the active site ⋆ Around 60 degrees, the enzyme stops working all together ⋆ Denaturation is a permanent change and the enzyme will not function again ⋆ The optimum working temperature varies from enzyme to enzyme, but most in our bodies work well at round 40 degrees

Answer 11

⋆ Although higher temperatures would slightly increase metabolic rate, the advantages are offset by the additional energy (food) that would be required to maintain a higher temperature ⋆ Other proteins apart from enzymes may be denatured ⋆ A further rise in temperature e.g. during illness might denature the enzymes

Answer 12

⋆ Alters the charges on the amino acids that make up the active site so the substrate can no longer attach to it and a complex cannot be formed ⋆ Causes the bond maintaining the tertiary structure to break, making the enzyme change shape so the substrate no longer fits with the active site and the enzyme is denatured ⋆ pH fluctuations inside organisms are usually small, so they are more likely to reduce an enzyme’s activity than to denature it

Answer 13

⋆ If we start off at low substrate concentrations and gradually increase the concentration whilst the enzyme concentration remains constant, the rate of reaction will increase because the active sites are not working to their full capacity ⋆ As more and more substrate is added, the active sites become gradually occupied ⋆ Eventually, all active sites are occupied so the rate of reaction levels off ⋆ In other words, there is an excess of substrate

Answer 14

⋆ Molecular shape similar to that of the substrate which allows them to occupy the enzyme’s active site ⋆ Competes with the substrate for active sites ⋆ The difference in concentration between the inhibitor and the substrate determines the extent to which the inhibitor will reduce the rate of reaction ⋆ Sooner or later, the substrate molecules will all occupy an active site, but this will take longer with more competitive inhibitors ⋆ An example of competitive inhibition occurs when with an important respiration enzyme that acts on succinic acid ⋆ Malonic acid can inhibit the enzyme because it has a similar molecular site

Answer 15

⋆ Attach themselves to the enzyme at a site other than the active site ⋆ This alters the shape of the enzyme and therefore the active site ⋆ The enzyme therefore cannot function ⋆ The difference in concentration between the substrate and the inhibitor is not significant, since the enzyme is denatured either way

2. Enzymes and the Digestive System Flashcards

(41 cards)