Cell Biology Topic 1.1

Cell Theory All organisms are composed of one or more cells. Cells are the smallest units of life. All cells come from pre-existing cells.

Supporting Evidence Cells were discovered in 1665 by Robert Hooke. Upon his discovery other scientists started to observe similar objects in both plants and animals. Unicellular organisms were found to perform all of the essential activities necessary to sustain life. Multicellular organisms cells were organized into tissues and those tissues in turn made up an organ. Several organs then worked together to carry out specific function creating an organ system.

Essential Activities (life functions) Metabolism / Synthesis Response to stimuli Homeostasis Growth Excretion Reproduction Nutrition

Possible Exceptions to the Cell Theory skeletal muscle fibers are larger and have many nuclei which are contradictory to typical cells fungal hyphae are (sometimes) not divided up into individual cells some tissues / organs contain large amounts of extracellular material – vitreous humour of eye – mineral deposits in bone – xylem in trees Viruses are not cells. They are capable of reproduction but they need cells in order to do it.

Exceptions to cell theory

Relative Size. 1m = 1000 mm 1mm = 1000μm 1μm = 1000nm Micrometers and Nanometers are the most commonly used units of measure when measuring cells and molecular objects.

Examples of Relative Size: Molecules Thickness of cell membranes Viruses Bacteria Organelles Cells of eukaryotes 1 nm (DNA 2 nm) 10 nm 100 nm 1 μm 1-10 μm μm

Determining Size Magnification = Size of image divided by size of specimen. Magnification = 300 µ (image) 20 µ (specimen) Magnification = 15x

Determining Size A student observes and draws an Amoeba, using the high power lens of a microscope. The diameter of the drawing is 100 mm. The actual diameter of the Amoeba is 100 µm. What is the magnification of the drawing? A B.100 C.400 D.1000 (Total 1 mark)

Size to Volume Ratio Rate of heat production / waste production / resource consumption of a cell is a function of it’s volume. Rate of exchange of materials and energy (heat) is a function of it’s surface area. The ratio of surface area to volume is a major factor in limiting cell size.

Surface to volume ratio

Once a cell become too large, it has trouble maintaining homeostasis The solution is to divide into 2 new, smaller cells

Emergent Properties Some unicellular organisms live together in colonies. Individual cells that are close to each other but independent of one another Example: Volvox

Emergent Properties An organism consisting of a single mass of cells that are fused together is considered multi cellular. Cells organized in cooperative groups to form a living organism show emergent properties Example: C. elegans

Emergent Properties Multicellular organisms show emergent properties. This is from the interaction of component parts. Cells in multicellular organisms differentiate to carry out specialized functions. This is achieved through gene expression. – Process where only certain genes are expressed at a time.

Cell Differentiation In multi cellular organisms, different cells have different jobs (they are specialized) A group of cells that all do the same job are known as a tissue The process where a cell develops into a specialized cell is called differentiation. There are 220 different types of cells in the human body

Cell Differentiation/Gene Expression There are approximately 25,000 genes in the human genome Every cell contains every gene. When a cell makes a protein from a gene, the gene is said to be “expressed”. Differentiated cells only express the genes that correspond to their function. Some specialized cells may use only half of the genes they contain

Stem Cells At early stages of human embryonic development, the ball of cells are called stem cells 2 key properties: 1.Capable of dividing over and over 2.Have not become specialized

Stargardt’s disease

Stem Cells

Potentially very useful to research scientists -provide a means of healing diseases -replace new organs -even possibly produce our food

Stem Cells Sources Early embryo cells Umbilical cord blood Adult stem cells from bone marrow, skin and liver

Stem Cells Sources See page 15 for benefits and risks of different sources of stem cells

Stargardt’s Disease A from of muscular dystrophy that affects the eyes Genetic disease caused by a recessive mutation of the ABCA4 gene This gene codes for a membrane protein used in active transport (Vitamin A builds up in cell) Photoreceptor cells begin to degenerate Destroys central vision

Stargardt’s Disease