L1 - Introduction to Cell Biology

Studying Cells

* to understand the tissues and organisms that cells compose in details,
* to determine what is “normal” so we can fix the “abnormal”,
* to understand how macromolecular systems and organelles work and cooperate to enable cells to function autonomously and in tissues

Cell

* the cell is a fundamental unit of life, the basic building blocks of all living things,
* the human body is composed of \~75 trillions of cells.

How to study cell

* hypothesis-driven experiments,


* Cells are isolated and maintained in vitro 
* Know how to view cells and what to look for 
* Identification of organelles 
* Identification and study of how proteins drive cellular mechanisms 

Cell Culture

* the technique used to grow cells or tissues outside the organism under strictly controlled conditions,
* cells are isolated from each from any tissue by breaking down the cell-cell and cell-matrix interactions by mechanical fermentation, trypsin, EDTA

Mechanical fragmentation

breaks tissue into smaller portions 

Trypsin

breaks down outer layer of proteins that sticks cells together 

EDTA

an ion chelator that chelates to calcium and magnesium 

* Integrin sticks cells togethers, needs calcium to be stickier 
* Magnesium and calcium also inhibit trypsin 

Cells in the Cell Culture

* supplied with proper nutrients (amino acids, minerals, vitamins, salts, glucose, etc), serum (insulin, growth factors)
* grown usually at 37 C in a CO2 incubator

CO2

creates an acid-base equilibrium within the media 

Yellow media (cell culture)

overgrowth and lactic acid production 

Purple media (cell culture)

lack of CO2 leading to an alkaline media 

Cells can grow

as adherent cell cultures or suspension cell cultures

Primary Cell Culture

* cells taken directly from an organism,
* usually divide a limited number of times (\~50 generations, Hayflick limit),
* undergo contact inhibition if cell density is high

Cell Line

* cells which are transformed and are able to grow indefinitely (immortal cells),
* less likely to exhibit contact inhibition

Hela Cell

* the first human cell line established in 1952 by George Get (Johns Hopkins University, Baltimore) from cervical carcinoma biopsy of Henrietta Lacks

Morphology of normal vs transformed fibroblasts

Normal cells have a Hayflick limit, transformed cells don't 

Cell Division

the process by which a parent cell divides into two daughter cells

Cell division

* usually occuusually occurs as part of a larger cell cycle in which the cell grows and replicates its chromosome before dividing,
* both symmetric and asymmetric cell division occurs during development and in adult stem cellsrs as part of a larger cell cycle in which the cell grows and replicates its chromosome before dividing,
* both symmetric and asymmetric cell division occurs during development and in adult stem cells

Symmetrical Division

produces two identical stem cells or differentiated daughters

Asymmetrical Division

* stem or progenitor cell generates,
* a copy of itself, which retains self-renewal ability and differentiation potential,
* and one daughter that enters the path of differentiation,
* or two differently differentiated daughters

Progenitor Cell

* stem cell can divide into progenitor cells that are an intermediary,
* can divide symmetrically,
* differentiated cell can no longer be further modified,
* a biological cell that can differentiate into a specific cell type,
* more specific than stem cells, can only differentiate into their "target" cell type

Embryonic stem cells

* can be maintained in culture and can form differentiated cell types,
* are pluripotent and can be grown indefinitely in culture under appropriate conditions,
* can also be induced to differentiate into precursors for various cell types

Pluripotent Stem Cells

* can form organoids in culture,
* stem cells possess the intrinsic program to divide, differentiate, and organize themselves into complex structures

Organoids

* brain organoids have organization and structure remarkably similar to the fetal brain,
* organoids advance to fetal development state, but do not proceed to the organization seen in an adult organ

Adult Stem Cells

* contained by most tissues,
* required to maintain and repair tissues,
* capable of generating a limited number of different cell types,
* located in stem-cell niche,

(Replace the intestinal epithelium every 5 days!)

Stem Cell Niche

* an area of a tissue in which stem cells are present in an undifferentiated and self-renewable state,
* adjacent cells interact with the stem cells to signal self renewal or differentiation

Reprogramming Mature Cells

obtain pluripotent cells from differentiated normal cells with Yamanaka factors

Yamanaka factors

three genes (Oct4, Sox2, Klf4) and one frequently expressed in cancer cells (c-Myc)

Retrovirus

inserts a DNA copy of its RNA genome into the DNA of a host cell that it invades, thus changing the genome of that cell

Induced Pluripotent Stem Cells (iPS)

* derived from skin or blood cells reprogrammed back into an embryonic-like pluripotent state,
* enables the development of an unlimited source of any type of human cell needed for therapeutic purposes

Therapeutic Application of iPS

* mass screening for screening therapeutic compounds,
* genetically modifcation to repair mutation and grow into new organ with in vitor differentiation for transplantation