Learning
Challenges
• YOU WILL HAVE A RESIT OF
YOUR CELLS AND MITOSIS
TEST NEXT WEEK ON
WEDNESDAY OR THURSDAY!!!
I WANT YOUR COMLETED LAB
BOOKS ON WEDNESDAY NEXT
WEEK!!!!!
Describe how a
phospholipids is
different to a
triglyceride
(D)
Identify the
relative parts
on a diagram of
the plasma
membrane (D)
Describe the
arrangement of
phospholipids,
proteins &
carbohydrates
using the fluidmosaic model ( C)
Describe and
explain the role
of carrier
proteins and
protein channels
in facilitated
diffusion. (C>)
Chapter 2.3
Objectives of unit:
• Understand the structure and properties of the plasma membrane
• Investigate the properties of plasma membranes practically
• Explain passive transport mechanisms of diffusion and facilitative diffusion,
including the role of transporter and carrier proteins
• Define the process of osmosis
• Explain the process of active transport and the role of proteins and ATP
• Explain the processes of endocytosis and exocytosis
• Describe the properties of gas exchange surfaces in living organisms
• Explain how the structure of the mammalian lung is adapted for rapid gaseous
exchange
Cells have many membranes:
plasma membrane
tonoplast
outer mitochondrial membrane
inner mitochondrial membrane
outer chloroplast membrane
nuclear envelope
Learning
Challenges
Describe how a
phospholipids is
different to a
triglyceride
(D)
Identify the
relative parts
on a diagram of
the plasma
membrane (D)
Describe the
arrangement of
phospholipids,
proteins &
carbohydrates
using the fluidmosaic model ( C)
Describe and
explain the role
of carrier
proteins and
protein channels
in facilitated
diffusion. (C>)
Membranes are flexible and able to break
and fuse easily
Neutrophil engulfing
anthrax bacteria.
Learning
Challenges
Describe how a
phospholipids is
different to a
triglyceride
(D)
Identify the
relative parts
on a diagram of
the plasma
membrane (D)
Describe the
arrangement of
phospholipids,
proteins &
carbohydrates
using the fluidmosaic model ( C)
https://www.yout
ube.com/watch?v
=Z_mXDvZQ6dU
Cover credit:
Micrograph by Volker
Brinkmann, PLoS
Pathogens Vol. 1(3)
Nov. 2005.
5 μm
Describe and
explain the role
of carrier
proteins and
protein channels
in facilitated
diffusion. (C>)
Membranes allow cellular compartments
to have different conditions
pH 4.8
Contains digestive
enzymes, optimum pH
4.5 - 4.8
lysosome
Membrane acts as
a barrier
pH 7.2
cytosol
Learning
Challenges
Describe how a
phospholipids is
different to a
triglyceride
(D)
Identify the
relative parts
on a diagram of
the plasma
membrane (D)
Describe the
arrangement of
phospholipids,
proteins &
carbohydrates
using the fluidmosaic model ( C)
Describe and
explain the role
of carrier
proteins and
protein channels
in facilitated
diffusion. (C>)
Membranes are mainly made of
phospholipids
phosphate
group
hydrophilic
head
phosphoester
bond
glycerol
ester bond
fatty acid
hydrophobic
tail
Learning
Challenges
Describe how a
phospholipids is
different to a
triglyceride
(D)
Identify the
relative parts
on a diagram of
the plasma
membrane (D)
Describe the
arrangement of
phospholipids,
proteins &
carbohydrates
using the fluidmosaic model ( C)
Describe and
explain the role
of carrier
proteins and
protein channels
in facilitated
diffusion. (C>)
Phospholipid
Learning
Challenges
Describe how a
phospholipids is
different to a
triglyceride
(D)
Identify the
relative parts
on a diagram of
the plasma
membrane (D)
Describe the
arrangement of
phospholipids,
proteins &
carbohydrates
using the fluidmosaic model ( C)
Describe and
explain the role
of carrier
proteins and
protein channels
in facilitated
diffusion. (C>)
Phospholipid
Learning
Challenges
Describe how a
phospholipids is
different to a
triglyceride
(D)
Identify the
relative parts
on a diagram of
the plasma
membrane (D)
Describe the
arrangement of
phospholipids,
proteins &
carbohydrates
using the fluidmosaic model ( C)
Describe and
explain the role
of carrier
proteins and
protein channels
in facilitated
diffusion. (C>)
The polar hydrophilic heads are water soluble and the
hydrophobic heads are water insoluble
Hydrophobic (water-hating) tail
air
aqueous solution
Hydrophilic (water-loving) head
Phospholipids form
micelles when
submerged in water
In 1925 Gorter and Grendel proposed that the
unit membrane is formed from a phospholipid
bilayer
Extracellular space (aqueous)
Cytosoplasm (aqueous)
Phosphate heads
face aqueous
solution
Learning
Challenges
Describe how a
phospholipids is
different to a
triglyceride
(D)
Identify the
relative parts
on a diagram of
the plasma
membrane (D)
Describe the
phospholipid
arrangement of
bilayer
phospholipids,
proteins &
carbohydrates
using the fluidmosaic model ( C)
Hydrophobic tails
face inwards
Describe and
explain the role
of carrier
proteins and
protein channels
in facilitated
diffusion. (C>)
Question: Explain why phospholipids form
a bilayer in plasma membranes (4).
• Phospholipids have a polar phosphate group which are
hydrophilic and will face the aqueous solutions
• The fatty acid tails are non-polar and will move away from an
aqueous environment
• As both tissue fluid and cytoplasm is aqueous
• phospholipids form two Click
layers
with the hydrophobic tails facing
to reveal answers
inward
• and phosphate groups outwards interacting with the aqueous
environment
• Click here to hide answers
Initial studies showed that the
plasma membrane had layers:
Scientists also found that protein were present in
membranes so Davson-Danielli proposed in 1935 the
following model for membrane structure:
Protein
Phospholipid
bilayer
Learning
Challenges
Describe how a
phospholipids is
different to a
triglyceride
(D)
Identify the
relative parts
on a diagram of
the plasma
membrane (D)
Describe the
arrangement of
phospholipids,
proteins &
carbohydrates
using the fluidmosaic model ( C)
Describe and
explain the role
of carrier
proteins and
protein channels
in facilitated
diffusion. (C>)
The development and use of electron
microscopes showed that the Davson-Danielli
model was incorrect
In the early 1970s Singer and Nicholson used
techniques such as freeze-etching to confirm the lipid
bilayer.
They also showed that the proteins were distributed
throughout the protein in a mosaic pattern.
In addition they found that the membrane was fluid and
had considerable sideways movement of molecules
within it.
Hence they proposed the Fluid-Mosaic Model for
Plasma Membrane Structure.
Learning
Challenges
Describe how a
phospholipids is
different to a
triglyceride
(D)
Identify the
relative parts
on a diagram of
the plasma
membrane (D)
Describe the
arrangement of
phospholipids,
proteins &
carbohydrates
using the fluidmosaic model ( C)
Describe and
explain the role
of carrier
proteins and
protein channels
in facilitated
diffusion. (C>)
Activity:
• Read pages 100 – 103 of your
textbook
• Answer questions 1 – 3 on page
103
Learning
Challenges
Describe how a
phospholipids is
different to a
triglyceride
(D)
Identify the
relative parts
on a diagram of
the plasma
membrane (D)
Describe the
arrangement of
phospholipids,
proteins &
carbohydrates
using the fluidmosaic model ( C)
Describe and
explain the role
of carrier
proteins and
protein channels
in facilitated
diffusion. (C>)
The fluid mosaic model of the
plasma
membrane:
The proteins can move freely through the lipid bilayer.
The ease with which they do this is dependent on the number of
phospholipids with unsaturated fatty acids in the phospholipids.
Fat-soluble organic molecules can diffuse through the
bilayer but polar molecules require proteins
diffusion
facilitated diffusion
Fat-soluble molecules
Learning
Challenges
Describe how a
phospholipids is
different to a
triglyceride
Polar molecules
(D)
Identify the
relative parts
on a diagram of
the plasma
membrane (D)
Extracellular
space
Describe the
arrangement of
phospholipids,
proteins &
carbohydrates
using the fluidmosaic model ( C)
Cytosoplasm
(aqueous)
hydrophilic pore
Describe and
explain the role
of carrier
proteins and
protein channels
in facilitated
diffusion. (C>)
Question 4: How can polar and
non-polar molecules pass
•Polar
molecules
proteins to enable
through
therequire
membrane
(2).them to pass through
the membrane
•Non-polar molecules can diffuse
directly through the phospholipid
Click to reveal answer
bilayer
Click here to hide answers
The membrane contains many
types
of
protein:
carbohydrate chain
Glycocalyx: For cell recognition
so cells group together to form
tissues
Receptor: for
recognition by
hormones
glycoprotein
peripheral protein
Enzyme or
signalling
protein
integral protein
carrier protein
hydrophilic channel
Question: Label the diagram
(11marks)
4
1
5
6
Note: label the proteins based on location or
structure, e.g. you do not need to identify
receptors and enzymes.
3
2
7
10
9
11
8
1) carbohydrate; 2) glycoprotein; 3)integral protein; 4) peripheral protein; 5) carrier protein 6)
hydrophilic channel; 7) phosphate group;
acid;
9) phospholipid;
Click 8)
tofatty
reveal
answers
10) glycocalyx; 11) phospholipid bilayer
click to cover answers
Question: Explain why the model
for membrane structure is
• The phospholipid molecules can move freely laterally and makes
known
as the
the membrane
fluid.fluid mosaic model
•(3).
The proteins are distributed throughout the membrane un
evenly and in a mosaic pattern.
• The agreed structure isClick
based
upon
experimental and chemical
to reveal
the answers
evidence and so is classed as a model.
• Click here to hide answers
Question: Describe the structure
and function of the glycocalyx (3)
• Consists of glycoproteins
• Which are proteins with added carbohydrate chains
• Used for cell recognition/receptors
Click to reveal answers
• Click here to hide answers
There are different types of
carrier proteins in the
membrane:
ATP
Carrier protein
(passive)
Gated-channel protein
Channel protein
Carrier protein
(active)
Membrane bound proteins allow chemical
processes to occur on membranes in a
sequential manner:
proteins
membrane
Cyt c
Q
I
III
II
Enzyme and transporter proteins
involved in aerobic respiration in the
inner mitochondrial membrane
IV
ATP synthase
Question: Other than as carrier
proteins state two functions of
•membrane
Receptors
bound proteins (2).
• Enzymes
• Structural (attached to microtubules)
Click to reveal answers
• Click here to hide answers
Practical Activity:
Factors affecting membrane permeability
• What experiment would you have done to
see this?
Permeability
Three factors affect the permeability of a cell
membrane:
 heat
 ethanol
 pH
Try and explain how these factors affect the
membrane, by referring to the fluid mosaic model.
Help
A temperature exceeding the optimum and pH levels beyond
the normal range can denature the membrane’s proteins.
Ethanol dissolves the lipid components of the membrane.
This all makes the membrane far more permeable acting as
if it is full of holes.
Membrane Permeability
Plasma membranes are semi-permeable – this means that some substances can pass through and
others cannot. What is it that determines what substances pass through? The substance has to be
very soluble in the oily phospholipid bilayer. Steroid hormones, oxygen and carbon dioxide are
examples of such molecules.
SOLUBLE
steroid hormone
oxygen
carbon dioxide
INSOLUBLE
Glucose
Protein
Lipid
Experiment
5°C
0.04
Absorbance %
Click the arrows to adjust the
temperature
Experiment
22.5°C
0.075
Absorption %
Experiment
40°C
0.12
Absorption %
Experiment
52°C
0.25
Absorption %
Experiment
60°C
0.64
Absorption %
Experiment
68°C
0.70
Absorption %
Results
Graph
Results Table
Graph to show change in membrane permeability
with an increase in temperature
Absorption/ %
5
0.04
22.5 (Room
Temperature)
0.075
0.8
0.7
0.6
Absorption / %
Temperature
(°c)
0.5
0.4
0.3
0.2
40
0.12
0.1
0
52
0.25
60
0.64
68
0.7
0
10
20
30
40
50
60
70
80
Tem perature/°C
4.6
Conclusion
The increase in temperature causes the proteins in the membrane to
denature and so its permeability increases, causing substances (purple
dye in this case) to escape.
Question 3: Describe an experiment by which you
could test to see whether alcohol concentration
affected membrane permeability (5).
• Same volume discs of beetroot
• Same volume of alcohol
• Same temperature
• Same time in alcohol
• Range of alcohol concentrations
Click to reveal answers
• Use colourimeter to read amount of pigment in solution
• Graph of colour intensity (% absorbance etc.) over alcohol
concentration
Click here to hide answers
Summary
•
The unit membrane consists of a phospholipid bilayer
•
Phospholipids consist of a polar, hydrophilic phosphate head and a nonpolar, hydrophobic tail consisting of fatty acid chains.
•
Proteins also occur in the membrane and float freely throughout it.
•
The model for membrane structure is known as the fluid mosaic model.
•
Peripheral proteins occur on the inner or outer face of the membrane
and integral proteins extend through both lipid layers.
•
Membrane bound enzymes occur allowing structured metabolic pathways.
•
Glycoproteins form the glycocalyx and allow cell to cell recognition.
•
Receptor proteins can act as binding sites for hormones and other
substances and can transmit the information to the interior of the cell.
•
A variety of carrier proteins allow for the controlled movement of
substance through the membrane using both passive diffusion or active
transport.
•
Non-polar, lipid soluble molecules diffuse through the phospholipid
bilayer.
•
Ionic, polar molecules require carrier proteins to enable them to pass
through the membrane.
•
Membrane structure loses integrity with high temperature or presence
of organic solvents such as alcohol, thereby increasing permeability.
Learning
Challenges
Describe how a
phospholipids is
different to a
triglyceride
(D)
Identify the
relative parts
on a diagram of
the plasma
membrane (D)
Describe the
arrangement of
phospholipids,
proteins &
carbohydrates
using the fluidmosaic model ( C)
Describe and
explain the role
of carrier
proteins and
protein channels
in facilitated
diffusion. (C>)