Cell Biology

Seite 1

Cell Theory:

1. All living things are composed of cells

2. Cells are the smallest unit of life

3. Cells can only come from pre-existing cells

Deviations of Cell Theory:

1. Striated muscle

- has multiple nuclei

- fuse to form very large cells

- deviates from the theory that cells perform autonomously

2. Giant Algae

- very large

- challenges the theory that large organisms are made up of microscopic components

3. Fungi

- some parts of the cells are not partitioned off by clear cell walls

- challenges the theory that organisms are made up of discrete cells

Seite 2

Functions of Life

M - Metabolism - living things undertake chemical reactions

R - Reproduction - living things must reproduce

H - Homeostasis - maintaining internal environment

G - Growth - change shape or size

R - Response - must respond to internal and external stimuli

E - Excrete - must be able to remove waste products

N - Nutrition - exchange materials and gasses with the environment

EXAMPLE:

Paramecium:

- Cilia allows it to move (response)

- Engulf food (nutrition)

- enzymes digest food (metabolism)

- Wastes are excreted via anal pore and contractile vacuoles (excretion)

- Essential gasses enter and exit via diffusion (homeostasis)

-Divide asexually (reproduction)

Seite 3

SA: Vol Ratio

- cells need to produce chemical energy to function

- larger cells need to produce more energy to sustain essential functions

- large membrane surface area equates to more material movement across the membrane

- as the cell grows, volume increases faster than surface area - the SA: Vol ratio decreases

*if the metabolic rate exceeds the rate of exchange of vital materials and wastes, the cell will die*

- growing cells need to divide to remain small and maintain a high SA: Vol ratio

Increasing SA: Vol ratio

- cells and tissues specialised for gas exchange will increase their surface area to optimise material transfer

Examples:

1. Villi within the intestines

2. Alveoli within the lungs

Seite 4

Magnification:

Magnification = Image Size (w ruler) / Actual Size

Actual Scale:

Actual Size = Image Size (w ruler) / Magnification

Seite 5

Emergent Properties:

- arise when the interaction of individual component produce new functions

- "The whole is greater than the sum of its parts"

- eg. multicellular organisms are capable of completing functions that unicellular organisms could not - due to collective actions of individual cells combining to create new effects

Examples:

- cells may be grouped together to form tissues

- organs are then formed from the functional grouping of multiple tissues

- organs that interact may form organ systems capable of carrying out specific body functions

- organ systems collectively carry out the life functions of the complete organism

Seite 6

Cell Differentiation:

Differentiation: the process during development whereby newly formed cells become more specialised and distinct from one another

- all cells of an organism share an identical genome

- the activation of different genes within a cell by chemical signals will cause it to differentiate

Gene Packaging:

within the nucleus, DNA is packaged with proteins to form a chromatin

- active genes are usually packaged in an expanded form call euchromatin that is accessible to transcriptional machinery

- inactive genes are typically packaged in a more condensed form called heterochromatin

Seite 7

Stem Cells:

When a cell differentiates and becomes specialised, it loses its capacity to form alternative cell types

Stem cells are unspecialised cells that have two key qualities:

1. Self Renewal - they can continuously divide and replicate

2. Potency - they have the capacity to differentiate into specialised cell types

Four types of Stem Cells:

1. Totipotent - can form any cell type, as well as embryonic tissue (eg. zygote)

2. Pluripotent - can form any cell type

3. Multipotent - can differentiate into a number of closely related cell types

4. Unipotent - cannot differentiate, but is capable of self renewal

Stem Cells are necessary for embryonic development - undifferentiated cell source from which other cells can be derived

Stem Cells are a viable therapeutic option when tissues become damaged