Post on 24-Jul-2018
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BIOH111
oCell Biology Module
oTissue Module
o Integumentary system
oSkeletal system
oMuscle system
oNervous system
oEndocrine system
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Textbook and
required/recommended readings
o Principles of anatomy and physiology. Tortora et al; 14th
edition: Chapter 3
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BIOH111 – Cell Module
o Session 1 (Lectures 1): Homeostasis and Cell
organisation and function of specific organelles
o Session 2 (Lectures 2 and 3): Central Dogma and plasma
membrane organisation and function
o Session 3 (Lectures 4): Cell communication (vesicular
transport) and extracellular matrix
o Session 4 (Lectures 5 and 6): Cell communication
(signalling) and Cell division
BIOH111
Session 2: Lectures 2 and 3
Central Dogma and plasma membrane
organisation and function
Department of Bioscience
endeavour.edu.au
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Preparation for this session
o Complete any missing concepts and linking words from
Session 1
o Make a model of plasma membrane (see Session 2
tutorial)
o Complete osmosis experiment and bring your
observations to next class (see Session 2 tutorial)
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Objectives
Lecture 2:
Central Dogma
Define central dogma
Describe transcription and translation and relate product of these
processes to their function
Lecture 3:
The plasma membrane
• Define structure of the plasma membrane and relate it to its functions
• Describe types of membrane proteins and define their structure and
function
• Define types of transport
• Describe passive and active transports
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Animal cell
Plasma membrane
Nucleus
Cytoplasm
Organelles
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NUCLEUS - function
Central Dogma:
DNA RNA proteintranscription translation
- double-stranded
- nucleus
- single-stranded
- nucleus & cytoplasm
- amino acid sequence
determines the structure
- anywhere in the cell
Base triplet Codon + anticodon amino acid
www.robotics.tu-berlin.de
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TranscriptionBase triplet
Codon
DNARNA
Definition: Process by which genetic
information encoded in DNA is copied onto a
strand of RNA called messenger RNA (mRNA).Gene – promoter + exons + introns
o Initiation: Promoter region initiates
transcription by RNA Polymerase binding
to a START base triplet ATG
o Elongation: RNAP reads a base triplet at
a time and makes a complementary
(antisense) RNA strand (mRNA) from
both intron and exon sequences; DNA
only unwrapped at the site of transcription
o Termination: RNAP stops transcribing
when it reaches a STOP base triplet
(TAA; TAG; TGA)
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NOTE: tRNA and rRNA are synthesised in the same way.
Post-Transcription Processingo Involves the formation of mature mRNA.
o Both, exons & introns, are copied onto the mRNA transcript during
Transcription.
Splicing
o The process of “editing” of the RNA transcript, when the introns are
removed to produce the mature mRNA molecule.
Stoker 2014, Figure 22-17 p811
For interest only
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TranslationDefinition: The process of reading the mRNA
nucleotide sequence to determine the amino
acid sequence of the protein
Codon & Anticodon
RNA
amino acid
Genetic code: 1 codon = 1 amino acid
o Initiation: mRNA with a START codon (AUG)
is first read by the ribosome with the antisense
tRNA anticodon (TAC) that caries amino acid
methionine)
o Elongation: mRNA is now a template for
ribosome to keep translating codons into
anticodons on tRNA which carry specific amino
acid; this process in the ribosome builds a
polypeptide chain that will become proteins
o Termination: once ribosome encounters a
STOP codon on mRNA, a corresponding tRNA
signals release of polypeptide chain from the
ribosome
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Stoker 2014, Figure 22-23 p823
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Codon table
Stoker 2014, Figure 20-13 p719
Tertiary Structure of a Protein
NOTE: what happens with a protein once it is made will be covered in detail in BIOB111
schoolworkhelper.net
www.diamond.ac.uk
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Objectives
Lecture 2:
Central Dogma
Define central dogma
Describe transcription and translation and relate product of these
processes to their function
Lecture 3:
The plasma membrane
• Define structure of the plasma membrane and relate it to its functions
• Describe types of membrane proteins and define their structure and
function
• Define types of transport
• Describe passive and active transports
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Animal cell
Plasma membrane
Nucleus
Cytoplasm
Organelles
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THE PLASMA MEMBRANE
o Function: flexible but sturdy barrier that surrounds the cell
o “Fluid mosaic” model
o Structure:
1. Lipids – 75% phospholipids, 20%cholesterols and 5% glycolipids.
2. Proteins – integral and peripheral membrane proteins with various
functions
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THE LIPID BILAYER
o Amphipathic
• Polar head and non- polar tails
o Cholesterol molecules are weakly amphipathic and are
interspersed among other lipids.
o Glycolipids only present in the outer membrane leaflet.
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Phospholipidso Comprises 75% of plasma
membrane lipids
o Phospholipid bi-layer = 2 parallel
layers of molecules
o Each molecule is amphipathic
(has both polar & non-polar
region)
• polar parts (heads) are hydrophilic
and face a watery environment both
inside and outside of the cell
• nonpolar parts (tails) are
hydrophobic and line up next to
each other in the interior of the bi-
layer
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o Comprises 20% of cell
membrane lipids
o Interspersed among the other
lipids in both layers
o Stiff steroid rings &
hydrocarbon tail are nonpolar
and reside within the bi-layer
o Lipid rafts – cell membrane
platforms of high cholesterol
and protein levels
Cholesterol
spartapoint.com
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o Comprise 5% of the lipids of
the cell membrane
o Lipid with a carbohydrate
group attached to its polar
head
o Carbohydrate groups form a
polar head only on the outside
membrane leaflet (facing the
extracellular fluid)
o Function: recognition from the
outside
Glycolipids
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MEMBRANE FLUIDITY
o Ensures free rotation and
movement of proteins and lipids
within the bilayer, helps in
formation of cell junctions and
allows the lipid bi-layer to self
seal if it is torn or punctured.
o Depends on the number of
double bonds in the fatty acid
tails of the lipids that make up
the bi-layer and amount of
cholesterol present.
MEMBRANE PERMEABILITY
o Selectively semi-permeable -
permeable to small, nonpolar,
uncharged molecules and water but
impermeable to ions and charged or
polar molecules.
o Ensures tight control of the cellular
homeostasis – e.g. if cell needs to
adapt its concentration of
intracellular ion levels it can do this
by free movement of water across
the membrane and control the
transport of that ion thus establishing
gradients
o Integral proteins and vesicular
transporttransport of large molecules
is tightly controlled
PHYSICAL PROPERTIES OF PLASMA
MEMBRANE
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GRADIENTS ACROSS MEMBRANEo Concentration gradient is the difference
in the concentration of a molecule
between two sides of the plasma
membrane.
• e.g. oxygen and sodium ions are more
concentrated outside the cell with carbon
dioxide and potassium ions more
concentrated inside the cell
o An electrical gradient is the difference in
the electrical charges across the bilayer.
• Inner surface of plasma membrane is more
negatively charged and outer surface is more
positively charged – this is called membrane
potential.
The combined concentration and electrical gradients
are called the electrochemical gradient.
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MEMBRANE PROTEINS
o Integral proteins extend into and
across the entire lipid bi-layer among
the fatty acid tails of the phospholipid
molecules. The transmembrane
domain is always a-helical.
o Peripheral proteins are found at the
inner or outer surface of the
membrane and can be stripped away
from the membrane without
disturbing membrane integrity.
o Many membrane proteins are
Glycoproteins.a-helix. Also see session 14 BIOB111
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Integral
o Ion channel
o Carrier/Transport protein
o Receptor
o Cell identity
o Linker
o Enzyme
Peripheral
o Cell identity
o Linker
o Enzyme
FUNCTIONS OF
MEMBRANE PROTEINS
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FUNCTIONS OF MEMBRANE
PROTEINS
o Ion Channel
• allow specific ion to pass
through a water-filled pore
• e.g. Na2+, K+, Cl- channels
o Transporter
• bind a specific substance,
change their shape & move
it across membrane
• e.g. amino acid (glutamate)
and glucose transporters
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FUNCTIONS OF MEMBRANE
PROTEINS
o Receptor Protein
• recognises specific
extracellular ligand and
alters cell’s function
• e.g. hormone receptors
o Cell identity marker
• allows for recognition of
“self”
• e.g. MHC proteins
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o Linker
• anchors intracellular and
extracellular filaments to the cell
membrane and allow cell
movement, cell shape & structure
• e.g. E-cadherin
o Enzyme
• catalyses reactions inside or
outside the cell
• e.g. lactase
FUNCTIONS OF MEMBRANE
PROTEINS
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Objectives
Lecture 2:
Central Dogma
Define central dogma
Describe transcription and translation and relate product of these
processes to their function
Lecture 3:
The plasma membrane
• Define structure of the plasma membrane and relate it to its functions
• Describe types of membrane proteins and define their structure and
function
• Define types of transport
• Describe passive and active transports
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Transport across the plasma membrane is
essential for maintaining cellular homeostasis
Active transport
o Primary
o Secondary
Passive transport
o Simple diffusion
o Facilitated diffusion
(channel & carrier)
o Osmosis
Vesicular transport
o Endocytosis
o Exocytosis
Types of transport:
- Small polar and non-polar molecules
- Amino acids
- Water - Macromolecules
- Organisms
Covered in next session
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Transport across the plasma membrane is
essential for maintaining cellular homeostasis
Passive transport
o Simple diffusion
o Facilitated diffusion
(channel & carrier)
o Osmosis
Types of transport:
- Small polar and non-polar molecules
- Amino acids
- Water
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PRINCIPLES OF DIFFUSION
Definition: Diffusion is the random mixing of particles (solute) that
occurs in a solution (solvent) as a result of the kinetic energy of the
particles. Molecules of solute and solution diffuse from high to low
concentration.
Diffusion rate across plasma membranes is
influenced by:
Steepness of the concentration gradient
Temperature
Size or mass of the diffusing substance
Surface area
Diffusion distance
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SIMPLE DIFFUSION
o Definition: passive process in which solute move freely through the lipid
bilayer of the plasma membrane of the cells without the help of membrane
transport proteins.
o e.g. nonpolar, hydrophobic molecules (respiratory gases, some lipids, small
alcohols, ammonia) and some polar molecules (water, urea, small
alcohols)
o Important for: gas exchange, absorption of some nutrients (e.g. vitamins
soluble in lipid (A,D,E,K)) and lipid-soluble hormones, and excretion of
waste
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o Rate of movement depends on:
• steepness of concentration gradient
• number of transporter proteins
(transport maximum)
o This type of diffusion exhibits
saturation
o e.g. glucose, urea, fructose,
galactose and some vitamins.
Transport maximum/
saturation
Definition: spontaneous passive process of solute movement
across a biological membrane via specific transmembrane
integral proteins (two types).
FACILITATED DIFFUSION
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FACILITATED DIFFUSION
1. Channel-mediated
• a solute moves down its concentration
gradient across the lipid bilayer through a
membrane channel.
o Most channels are ion channels, allowing
passage of small, inorganic ions which are
hydrophilic (e.g. K+, Na2+, Ca2+, Cl-)
o Ion channels are selective and specific on
the ion’s shape and charge and may be
gated (e.g. K+ channel) or open all the time.
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FACILITATED DIFFUSION2. Carrier-mediated
• a carrier is used to move a solute down its
concentration gradient across the plasma
membrane.
o The molecule binds to a carrier on one side
of the plasma membrane which causes the
carrier to undergo a change in shape so that
molecule can be released on the other side.
o Solute binds more often on the side of
membrane with higher concentration so this
process depends on the steepness of
concentration gradient across the membrane.
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E.g. facilitated diffusion of glucose
o Glucose binds to transport
protein
o Transport protein changes
shape
o Glucose moves across cell
membrane (but only down
the concentration gradient)
o Kinase enzyme reduces
glucose concentration inside
the cell by transforming
glucose into glucose-6-phosphate
http://weill.cornell.edu/biochem/mcgraw/insulin-regulated.html
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OSMOSISDefinition: osmosis is the net movement of a solvent through a
selectively permeable membrane, or in living systems, the movement of
water (the solvent) from an area of higher concentration to an area of
lower concentration across the membrane.
• Water molecules penetrate the
membrane by simple diffusion through
the lipid bilayer or through aquaporins,
transmembrane proteins that function as
water channels.
• Water moves from an area of lower solute
concentration to an area of higher solute
concentration.
• Osmosis occurs only when the
membrane is permeable to water but
not to certain solutes.
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o Osmotic pressure of a solution is proportional to the concentration of the
solute particles that cannot cross the membrane. Osmotic pressure helps
to maintain cell volume and prevents diffusion of water molecules.
o Hydrostatic pressure – pressure exerted by the liquid, promotes diffusion
of water form high to low concentration.
o Osmotic pressure – force exerted by the impermeable solutes in the
solution (number of molecules)
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TONICITYDefinition: Tonicity is a measure of a solution’s ability to change
the volume of cells by altering their water concentration.
There are important medical uses of isotonic, hypotonic, and hypertonic solutions.
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ACTIVE TRANSPORTDefinition: an energy-requiring process that moves solutes
such as ions, amino acids, and monosaccharides against a
concentration gradient.
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PRIMARY ACTIVE TRANSPORT
e.g. Na+/K+ pump (also called Na+/K+ ATPase – why?):
• requires 40% of cellular ATP
• Ubiquitously and highly expressed
• maintains low concentration of Na+ and a high concentration of K+ in the
cytosol
• Cystic fibrosis
Definition: energy derived from ATP changes the shape of a
transporter protein, which pumps a substance across a plasma
membrane against its concentration gradient.
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SECONDARY ACTIVE TRANSPORT
o In secondary active transport, the energy stored in the
form of a sodium or hydrogen ion concentration gradient
is used to drive other substances against their own
concentration gradients.
o Plasma membranes contain several antiporters and
symporters powered by the sodium ion gradient.
o Symporters – move two substances in same direction
o Antiporters – move two substances in the opposite
directions across the membrane
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e.g. Na+/glucose symporter
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e.g. Na+/Ca2+ antiporter
1. Primary active transport via Na+/K+
ATPase (3 Na+ out/ 2 K+ in) drives
increase of Na+ outside the cell.
2. Transport of Na+ ions back into the
cell via Na+/Ca+2 antiporter (does not
need energy for function) allows
transport of Ca+2 out of the cell (net
effect: 3 Na+ in/ 1 Ca+2 out)
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Digitalis
Using the diagram above, explain what is the outcome of the use
of digitalis (inhibits Na+/K+ ATPase) on intracellular calcium levels
in cardiac muscle cells and ultimately heartbeat. What type of
patients may benefit from this treatment?
Relevance
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Recap of Session 2o Nucleus – contains DNA which is used as a template for
producing proteins in a process called central dogma
(transcription and translation) https://www.youtube.com/watch?v=2BwWavExcFI
o Plasma membrane structure contains proteins and lipids –
each are responsible for different plasma membrane
functions:
Fluid Mosaic Model https://www.youtube.com/watch?v=EL-A21k12k8
Membrane transport proteins
https://www.youtube.com/watch?v=tSJ0LnOHpTw
o Plasma membrane function of transport depends on the size
and charge of the particle being transported
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Recap of plasma membrane
structure
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Preparation for next session
o Complete any missing concepts and linking words from
Session 2
o Bring the model of plasma membrane to Session 3
o Revise the plasma membrane structure and function for
easier understanding of vesicular transport