BIOH111 SN02 Cells - … · oCell Biology Module oTissue ... Homeostasis and Cell organisation and...

© Endeavour College of Natural Health endeavour.edu.au 1

BIOH111

oCell Biology Module

oTissue Module

o Integumentary system

oSkeletal system

oMuscle system

oNervous system

oEndocrine system


Textbook and

required/recommended readings

o Principles of anatomy and physiology. Tortora et al; 14th

edition: Chapter 3


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


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)


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


Animal cell

Plasma membrane

Nucleus

Cytoplasm

Organelles


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

http://www.robotics.tu-berlin.de/menue/research/protein_structure_prediction/


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


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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Codon table


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

http://schoolworkhelper.net/protein-structures-primary-secondary-tertiary-quaternary/

http://www.diamond.ac.uk/Home/News/LatestNews/17_03_11.html

beautifulproteins.blogspot.com

http://beautifulproteins.blogspot.com/


Objectives

Lecture 2:

Central Dogma




Lecture 3:

The plasma membrane



function




Animal cell

Plasma membrane

Nucleus

Cytoplasm

Organelles


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


THE LIPID BILAYER

o Amphipathic

• Polar head and nonpolar tails

o Cholesterol molecules are weakly amphipathic and are

interspersed among other lipids.

o Glycolipids only present in the outer membrane leaflet.


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


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

http://spartapoint.com/2011/11/15/i-love-cholesterol/


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


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


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.


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


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


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



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


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


PROTEINS


Objectives

Lecture 2:

Central Dogma




Lecture 3:

The plasma membrane



function




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


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


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


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


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


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.


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.


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


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.


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)


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.


ACTIVE TRANSPORTDefinition: an energy-requiring process that moves solutes

such as ions, amino acids, and monosaccharides against a

concentration gradient.


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.


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


e.g. Na+/glucose symporter


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)


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


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

https://www.youtube.com/watch?v=2BwWavExcFI

https://www.youtube.com/watch?v=EL-A21k12k8

https://www.youtube.com/watch?v=tSJ0LnOHpTw


Recap of plasma membrane

structure


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

BIOH111 SN02 Cells - … · oCell Biology Module oTissue ... Homeostasis and Cell organisation and...

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Transcript of BIOH111 SN02 Cells - … · oCell Biology Module oTissue ... Homeostasis and Cell organisation and...