Starter

1
Starter no books

• Label the structures of the membrane
• Explain the term fluid mosaic
• Explain How you identify the outside of the
  plasma membrane

2
Learning objectives

• (e) outline the effect of changing temperature on
  membrane structure and permeability
• (f) explain the term cell signalling
• (g) explain the role of membrane-bound receptors
  as sites where hormones and drugs can bind

3
Membranes and temperature

• Kinetic energy effects the membrane just as it
  affects everything else
• This results in leaky membranes where
  substances which normally cannot pass through,
  seep through the larger gaps
• The more fluid a membrane is the more permeable
  it becomes

4
Explain the following statements

1. As temperature decreases so does the fluidity of
   the membrane
2. Organisms which live in high temperatures have
   more saturated fatty acids in their phospholipids

5
Cell signalling and recognition

• All cells must be able to identify changes in
  its surroundings, only then can it respond to
  them
• Two main ideas on cell signalling.
• a) White blood cells identify body cells as
  belonging
• b) All cells respond to hormone levels in the
  blood (different cells different hormones)

6

• In order to detect signals, cells must have
  sensors on their surfaces capable of receiving
  signals (receptors)
• These receptor are often protein molecules or
  modified protein molecules
• Look at fig 2.5 page 27 for ideas of these
  receptors (extension for explanations)

7
Hormone receptors _insulin

• Only certain cells will have receptors for a
  particular hormone (target cells)
• Insulin and insulin receptor must fit together
  perfectly (lock and key) we say their shapes are
  complementary to each other (NOT same shape)

8

• Increased blood sugar levels in blood
• Detected by (beta-cells) in islets of langerhans
  in pancreas
• Increased insulin production and release into
  blood
• We want to store this glucose in the liver and
  muscles for later use (receptors)
• Insulin binds and has two effects
• a) increased glucose channels to open
• b) conversion of glucose to glycogen inside
  cells

9
Pros and cons of this mechanism

• Medicinal drugs
• Made in a complementary shape to receptor
  molecule
• beta blockers block increases in heart rate
  when it can be dangerous
• Schizophrenia mimmick neurotransmitter that a
  person cannot make

• Viruses and poisons/toxins
• Viruses bind to receptor and use them as a way
  into the cell
• Toxins bind and block the normal response as
  the normal agent cannot bind (like enzyme
  inhibitors) BOTOX

10
How well do you get it?

1. Suggest how flu viruses infect human cells of the
   respiratory tract
2. Name two target tissues for insulin
3. Botulinum toxin binds to the ends of nerves and
   prevent them releasing chemicals that normally
   cause muscles to contract. There are 8 different
   botulinum toxins, some stronger than others.
   Suggest why some are more potent than others