Lesson starter

Give one similarity and one two differences between active transport and facilitated diffusion

Both require a protein carrier moleculeActive transport requires energy/uses ATP, but facilitated diffusion occurs down a concentration gradient

Preventing blood loss

Learning objectives

(a) describe the first-aid procedure to prevent excessive blood loss;

(b) outline the mechanism of blood clotting as an enzyme controlled process, with reference to the role of platelets, damaged tissue, thromboplastin, calcium ions, prothrombin, thrombin, fibrinogen and fibrin;

(c) state that enzymes are globular proteins;

(d) explain how the structure of a globular protein enables enzyme molecules to catalyse specific metabolic reactions, with reference to the specificity of the active site, the formation of enzyme substrate complexes and the lowering of activation energy;

Preventing excess blood loss• In all cases of severe cuts, medical help should be sought immediately.• Trained first aiders can help to stem the flow of blood by carrying out the

following:1. Put on gloves if possible2. Reassure the person – sit or lie them down3. Inspect the wound – check nothing is in the wound or cut clothing to get a

better look4. If there is nothing in the wound, place a large, clean pad over the area and press

down firmly with your hand5. Use a bandage to hold the pad firmly in place6. If there is an object in the wound, do not remove it. Make a pad in the shape of

a ring and place it on the wound to surround the area7. Now use a bandage to apply pressure to the areas around the wound to push

the edges together8. If wound is on a limb, raise it higher e.g. cushions, raising arm etc9. If blood soaks through, do not remove the first pad, simply place another on

top.

How blood clots• Collagen fibres in the connective tissue (scaffolding material in your skin)

are exposed and platelets stick to them

• Platelets release chemicals that make them sticky – they start to form a plug. Calcium is needed for this to happen

• WBCs (leucocytes) collect at the cut site and release the enzyme thromboplastin, which catalyses this reaction, again with the aid of calcium ions:

Prothrombin thrombinthromboplastin

“switched off” enzyme “switched on” enzyme

How blood clots• A large plasma protein called fibrinogen is broken down by the addition of water (hydrolysis)

into smaller units

• These smaller units can re-arrange into a large, insoluble mesh-like protein called fibrin

• This process also requires calcium ions.

• The tangled mesh of fibrin helps to trap other blood cells, forming a blood clot

• The clot dries, forming a scab. This plug prevents blood loss and bacteria from entering the body via the wound

Enzymes• Thrombin in an enzyme. Enzymes are proteins that catalyses a specific

reaction, by lowering the activation energy needed for the reaction.

• The energy that it takes for molecules to react is called the activation energy – the lower this energy level is, the easier it is for the reaction to start.

• Enzymes are able to lower the activation energy of a reaction because of their highly specific tertiary structure

Enzymes

Enzymes• Know the specific words and phrases that are used when

talking about enzymes:– Active site– Substrate– Enzyme-substrate complex– Activation energy– Reactants– Products– Complementary shapes

• Also remember that enzymes are globular proteins.

Exam questions - plenary

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How did you do?

• The exam questions are a self assessment tool.

• If you found these questions difficult, you have not understood (or done) the pre-reading/textbook questions.

• Be honest with yourself – are you working as hard as you can?!