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Cell Biology & Genetics


Dr. Marco Brotto

on 7 September 2014

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Transcript of Cell Biology & Genetics

From Chapter 1: six characteristics of life
Organization (structures, compartments, organelles)
Metabolism (produce and breakdown biomolecules)
Responsiveness (to environment/other cells)
Growth (change in size, shape, composition)
Development (differentiation/specialization)
Reproduction (mitosis)

What can a cell do (what is “life”)?

A cell is the minimum requirement for life
This means we define life as being able to do what a cell can do...
Question: Is a single cell of a multicellular organism equivalent to “life”?
If no or maybe, what else is/are required? How do you decide?
All of your cells (trillions!) can be traced back to a single cell (fertilized egg)
All cells of all organisms trace back to an original cell = origin of evolutionarily successful “life”
All living things share the same basic building blocks (cells)

What does cell theory mean?

Mediated Transport
Facilitated diffusion
Active transport
Secondary active transport

3.6 Movement through the Plasma Membrane

Chemical Signals: Activation of G-proteins

Chemical Signals
Results of ligand-receptor binding
The ligand is the “first messenger”

Changes permeability of plasma membrane
Alters activity of cellular enzymes
Alters activity of G proteins
Alters gene expression

Saturation of a Receptor or Carrier


Chemical Signals
Ligand-Receptor Binding Characteristics

Peter Agre
Nobel Prize in Chemistry 2003

Discovered the water channel Aquaporin 1 in 1991

Coming soon… A&P link for
Nobel Prize winners!

Receptor molecules linked to channel proteins
Attachment of receptor-specific ligands (e.g., acetylcholine) to receptors causes change in shape of channel protein
Channel opens or closes
Changes permeability of cell to some substances, particularly ions.
Cystic fibrosis: defect in gene causes defect(s) in Cl- channel proteins
Drugs used to alter membrane permeability through attachment to channel protein-linked receptors (hypertension treatment)

Receptors Linked to Channel Proteins

Proteins in membranes with an exposed receptor site

Can attach to specific ligand molecules and act as an intercellular communication system

Ligand can attach only to cells with that specific receptor

Receptor Molecules

A quick search exercise: Go online to www.pubmed.com and search for “CHANNELOPATHIES”

Non-gated ion channels
Responsible for the permeability of the plasma membrane to ions
when the plasma membrane is at rest

Ligand gated ion channel:
Open in response to binding of small molecules (Hormones, neurotransmitters)

Voltage-gated ion channel:
Open when there is a change in charge across the plasma membrane (Action potential)

Channel Proteins

Intracellular trafficking of integrins in cancer cells. Pharmacol Ther. 2013 May 24. S0163-7258(13)00122-8.
Integrins as a potential target for targeted anticancer therapy. Biomed Khim. 2013 May-Jun;59(3):239-48.
Integrins and metastasis. Cell Adh Migr. 2013 May-Jun;7(3):251-61.
Genetic etiologies of leukocyte adhesion defects. Etzioni A. Curr Opin Immunol. 2009 Jul 31.
Expression of selected adhesion molecules in dermatitis herpetiformis... Pol J Pathol. 2009 Mar;60(1):26-34.

Integrins, membrane-bound proteins

Attachment sites to other cells or to extra/intracellular molecules.

Cadherins – attach cells to other cells

Attachment Proteins

Integral or intrinsic
Extend deeply into membrane, often extending from one surface to the other
Can form channels through the membrane
Peripheral or extrinsic
Attached to integral proteins at either the inner or outer surfaces of the lipid bilayer
Functioning depends on 3-D shape and chemical characteristics.
Markers, attachment sites, channels, receptors, enzymes, or carriers.

Membrane Proteins


How big are cells? How does the internal activity of cells look like?

1. The cell is the basic unit of life
2. All living organisms are composed of one or more cell(s)
3. All cells arise from pre-existing cells

Cell theory

How would you call
this enzyme?


K+ leak
(always open)

Gated Na+
Channel (closed)

Gated Na+



Allow cells to identify one another or other molecules
Immunity (auto-immune diseases)
Recognition of oocyte by sperm cell
Intercellular communication

Marker Molecules: Glycoproteins and Glycolipids

Dr. Marco Brotto
(with special thanks to my friend and collaborator
Dr. Matthew Stern)

Chapter 3
Cell Biology and Genetics




The general consensus and the answer based on our definition of life is NO

Virus = DNA or RNA + protein shell = complex assembly of molecules/chemicals
Viruses are not “biochemically autonomous”
No metabolism, relies upon host cell machinery
No reproduction, relies upon host cell machinery

Food for thought: http://www.scientificamerican.com/article.cfm?id=are-viruses-alive-2004

Question: Is a virus alive? Why or why not?

The carrier protein changes shape and releases
the transported molecule on the other side of the
plasma membrane. The carrier protein then
changes back to its original shape (go to step 1).


The carrier protein briefly binds the transported molecule.

Carrier Proteins or Transporters -
Carrier proteins can be:

Uniporters – moves one particle

Symporters – move two particles in the same direction at the same time

Antiporters – move two particles in opposite directions at the same time

Separation of intracellular vs. extracellular materials

Semi-permeable membrane

Production of charge difference (membrane potential) across the membrane by regulation of intracellular and
extracellular ion concentrations

Outside of membrane positively charged compared to inside because of gathering ions along outside and inside (Membrane potential, Allows the cell to receive messages from and send messages to other cells)

Glycocalyx: combinations of carbohydrates and lipids (glycolipids) and proteins (glycoproteins) on outer surface.

Phospholipid bilayer and cholesterol (fat is essential to life! It does not mean that we “fast fat”!!!)

Fluid-mosaic model

3.3 Plasma Membrane






Requires ATP. The use of energy allows the cell to accumulate substances
Rate of transport depends on concentration of substrate and on concentration of ATP

ATP-Powered Transport








Alter activity on inner surface of plasma membrane
Leads to intracellular chemical signals that affect cell function
Many hormones function in this way

Receptors Linked to G Protein Complexes

Summary of Membrane Proteins

Enzymes: some act to catalyze reactions at outer/inner surface of plasma membrane.
Surface cells of small intestine produce enzymes that digest dipeptides

A molecule enters the carrier protein from one side of the plasma membrane.



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