Topic 2 Cells

Cell theory• All living things are made up of cells

• Cells are the smallest unit of life

• All cells come from other cells

What is the evidence for the cell theory ?

All living things are made up of cells

• All 5 kingdoms of life are made up of cells

• Some organisms are only one-celled, unicellular

• We can observe cells under the microscope

What is the evidence for the cell theory ?

Tissues are made up of individual cells that can be isolated

Cells can live in vitro but organelles can’t.

Cells are the smallest unit of life

What is the evidence for the cell theory ?

Mitosis and meiosis have been observed many times in many different organisms

Mixing the components of cells together has never resulted in the formation of a cell

Cells arise from other cells

Exceptions to the rule

Muscle cells- have lost the membrane between them and so are long cells with many nuclei

Fungi cells- also very long and multi-nucleated

More exceptions…..

•Virus is non cellular, just some DNA or RNA surrounded by a protein coat…there is debate about whether it is alive or not.

•Mitochondria and chloroplasts have their own DNA and can replicate themselves but they are organelles not cells. They are believed to have once been free living prokaryotic cells that formed a symbiotic relationship with a eukaryotic cell.

Unicellular organisms Some organisms like many protista and all prokaryotes are only one cell big but they are able to carry out all the functions of life.

a. metabolism which includes respiration the synthesis of ATP.

b. response to a change in the environment

c. homeostasis the maintenance and regulation of internal cell conditions.

d. growth which for a unicellular organism means an increase in cell size and volume.

e. reproduction which for the unicellular organism is largely asexual through cell division to form a clone.

f. nutrition which means either the synthesis of organic molecules or the absorption of organic matter.

Amoeba on the move!

Diatoms

Multicellular cells show emergent properties

Emergent properties are ones that come about when individual parts of a system interact with each other. On their own, the individual parts cannot do what they can do together.

The whole is greater than the sum of its parts.

A cell can do much more than the individual parts or organelles can do.

A protein can do more than the amino acids that its made up of.

Think of these 3 parts:

1. A small metal cup

2. A glass bowl

3. A piece of tugnsten wire

Individually they have no function, but when they are together:

Relative sizes:1. Molecules (1nm)2. Cell membrane thickness (10nm)3. Virus (100nm)4. Bacteria (1µm)5. Organelles (less than 10µm)6. Cells (less than 100µm)7. Generally plant cells are larger than animal cells

Why do cells not grow to larger sizes?

Answer!Surface-area to Volume Ratio!

Rate of heat and waste production and rate of resource consumption are functions that depend on its volume

Most chemical reactions takes place inside the cell and its size affects the rate of these reactions

The rate of exchange of substances therefore depends on the organisms surface area that is in contact with the surroundings

As the organism gets bigger, their volume and surface area both get bigger, but not by the same amount

Cell radius Cell radius (r)(r)

0.25 units0.25 units 0.5 units0.5 units 1.25 units1.25 units

Surface Surface areaarea

0.79 units0.79 units 3.14 units3.14 units 7.07 units7.07 units

VolumeVolume 0.06 units0.06 units 0.52 units0.52 units 1.77 units1.77 units

SA: VolumeSA: Volume 13.17:113.17:1 6.04:16.04:1 3.99:13.99:1

Conclusion

Large organisms, the rate of exchange of substances with their surroundings occurs more slowly

Benefits of Light Benefits of Light MicroscopeMicroscope

Benefits of Benefits of Electron Electron

MicroscopeMicroscope

1.1. Can see things in Can see things in colourcolour

2.2. Can look at live Can look at live organismsorganisms

3.3. Much cheaper to Much cheaper to buy & easy to buy & easy to operateoperate

1.1. Greater Greater magnificationmagnification

2.2. Great resolutionGreat resolution

Comparisons of microscopes:

Light microscope is more limited by its resolving power but allows observation of living organisms, movement and processes

Transmission electron microscope is used to study the internal structure of the cell

Scanning electron microscope is used to study the surface of a sample

Looking at cells: the microscopeTwo factors when evaluating a microscope:

1. Resolving power: a measure of the clarity of the image, the minimum distance two points can be and still be seen as two separate points

2. Magnification: how much bigger the image is, the ratio between the actual size and the image.

The limiting factor for a microscope is the resolving power. For light microscopes the shortest wavelength of light enables discrimination of 0.2 microns, the size of a bacteria, magnification is limited to 1000X

Electron microscopes use electrons and so their resolving power is 0.1 nanometers

Units of size

Calculating magnification

When you see an image like the ones on the last slide of cells (called a micrograph) they appear bigger than they actually are because they are magnified

You need to know how to calculate the magnification and the actual size of the specimen from a micrograph

Magnification=size of image/size of specimen

Size of specimen= size of image/magnification

Example:

Use the scale bar on the micrograph. 1um measures 9mm

Convert the 2 measurements to the same units

There are 1000um in 1mm, so 9mm= 9000um

Plug into the formula:

M= image size/specimen size

9000/1=9000X

To determine the actual size of something on the micrograph:

Measure it-example the mitochondria is 11mm and then use the formula:

Size=image/magnification

11,000um/9000=1.2 um

Is this a reasonable size for an organelle?

Estimating with help

You can also estimate the size of a cell or organelle by using a very small ruler that is etched into a microscope slide, called a micrometer.

You can measure the size of the field of view under different magnifications and use this to estimate the size of something under the microscope.

Virtual Microscope Lab!

http://www.udel.edu/biology/ketcham/microscope/scope.html

http://nhscience.lonestar.edu/biol/dropdrag/index.htm

http://nhscience.lonestar.edu/biol/dropdrag/micro.htm

Practice with the microscope

First go through the virtual microscope tour. We do not have binocular microscopes, or light rheostat, otherwise same. Follow directions- you will get a green check when you have done the task successfully. View an image under 3 powers, adjusting light and focus.

Then do the activity

Cell differentiation

All multicelluar organisms start out from one cell.

All cells in an organism (except gametes) have the exact same genetic information which guides all the structure and functions of the organism.

How how is it that a skin cell looks totally different than a nerve cell and that they do completely different things?

Cell differentiation

This quality of cells in different tissues having different structure and function is the result of cell differentiation.

This difference is not due to a difference in the DNA or genes but in how the genes are controlled or expressed.

• Once a cell has developed into a certain kind of cell it cannot be reprogrammed to become another kind of cell.

Stem cells• Stems cells are unspecialized cells. They can reproduce indefinitely and

have the capability of differentiation.

• They have the ability to become any kind of cell. This is called totiopotency. Cells that can become almost any kind of cell are called pluripotent.

• Human embryo is made up of stem cells up about 5 days old- called the blastula stage.

• These cells can be made to differentiate into almost any cell type. This is why they are the focus of so much research.

• Adults also have stem cells- these can’t make any kind of cell but they can make many different kinds. Ex: bone marrow stem cells can make all the different kinds blood cells as well as bone and muscle cells.

Embryonic stem cells/adult stem cells

Uses of stem cells

• Tissue repair

• Treatment of disease- Parkinson’s disease, multiple sclerosis, leukemia

• Possible growth of organs

• http://learn.genetics.utah.edu/units/stemcells/whatissc/

Why are cells small?

•As the size of a sphere increases, the volume increases more than the surface area.

•The surface area to volume ratio is important because materials must enter and leave the cell through the cell membrane. If the volume of the cell gets too big, the surface area can’t keep up with exchange of materials needed to support the metabolic activities of the cell.

So cells maintain a high surface area-to-volume ratio

Two kinds of cells: prokaryotic and eukaryotic

Prokaryotic

Small- 1 micron

Lack nucleus and intermembranous systems

Have cell wall

DNA: one main circular chromosome and additional DNA in plasmid

Two kinds of cells: prokaryotic and eukaryotic

Prokaryotic Eukaryotic

Small- 1 micron Larger-10-100 microns

Lack nucleus and intermembranous systems

Organelles bound by membranes

Have cell wall May have cell wall

DNA: one main circular chromosome and additional DNA in plasmid

DNA: in the nucleus, double stranded, no plasmid

Prokaryotic cells• Draw a diagram of the ultrastructure of Escherichia coli.

Include:

• Cell wall

• Plasma membrane

• Cytoplasm

• Pilli

• Flagella

• Ribosomes

• Nucleiod region

Generalized prokaryotic cell

Functions • Cell wall: made of peptidglcans (sugars and proteins),rigid

structure, protects cell gives it shape, prevents entry of water

• Plasma membrane: regulates what goes in and out of cell

• Cytoplasm: fluid inside cell, has enzymes, metabolic reactions

• Pili: hair like structures that can move in and out of cell. Allows one cell to attach to another

• Flagellum: made of proteins provides locomotion in some bacteria

• Ribosomes: protein synthesis

• Nucleoid region: DNA located here (genetic info), no nuclear membrane

Prokaryotic cells divide by binary fission

EUKARYOTIC CELLS

NUCLEUS

nucleus• Structure:

• Double membrane, continuous with ER

• Contains DNA and proteins

• DNA wound around proteins organized into chromosomes

• Perforated by pores

• Nucleolus inside

• Function:

• DNA is code for proteins, genetic information

• Nucleolus made up of ribosomal RNA, which makes up the ribosomes where protein synthesis happens

• Pores allow mRNA and rRNA to leave nucleus

RIBOSOMES

ribosomes

• Structure:

• Made of rRNA and protein

• Small and large subunits

• Some are attached to endomembranous system, some are free

• Function

• Site of protein synthesis

• Proteins made on bound ribosomes are secreted outside the cell

• Proteins made on free ribosomes are used inside the cell.

ENDOMEMBRANE SYSTEM

Endoplasmic reticulum

membrane system• Structure:

• Made of a phospholipid bilayer similar to the membrane around the cell

• Organelles are surrounded by membranes

• It goes from the nuclear envelope out to the edge of the cell

• Functions:

• Regulation of protein traffic from the ER to vesicles

• Metabolic functions: the inner membranes of mitochondria and chloroplasts

endoplasmic reticulum• Smooth ER has no

ribosomes, has enzymes embedded in the membrane

• Rough ER has ribosomes

• Smooth ER: synthesis of lipids, metabolism of carbohydrates, detoxification of drugs and poisons.

• Stores Ca++ in muscle cells

• Rough ER: synthesis of proteins and glycoproteins

• Makes membrane proteins and phospholipids that makes up its own membrane

Golgi Apparatus

Golgi apparatus• Structure:

• Flattened, membranous sacs called cisterns

• The inside of each sac is kept separate from the cytosol

• Two faces: cis and trans. cis faces the ER and trans faces the outside of the cell

• Function:

• Products from the ER come to the cis face in vesicles

• Proteins and phospholipids are modified

• Makes polysaccharides and other macromolecules

• Products leave from the trans face in vesicles, these can go to other places in the cell or to the membrane for secretion. Products are tagged chemically so they go to the correct places

Lysosome

lysosome

• Structure:

• Membranous sac with digestive enzymes

• Only in animal cells

• Functions:

• Intracellular digestion of macromolecules

• Recycling of damaged organelles called autophagy

vacuoles

• Similar to lysosomes, have hydrolytic enzymes

• Present in plant and fungi, protista

• Functions:

• Food vacuoles store food

• Contractile vacuoles in protists control water and salts

• Plants have central vacuole that gives internal support, stores organic molecules, pigments, poisons

mitochondria• Structure:

• Double membrane

• Inner membrane has infolds called cristae

• Inside is called matrix

• Has its own DNA and ribosomes

• Enzymes embedded into the membrane and in the matrix

• Function:

• Synthesis of ATP from glucose cellular respiration

chloroplast

• Structure

• Double membrane

• Inner compartment made up of another intermebranous system called thylakoids

• Fluid around the thylakoids called stroma

• Function

• Photosynthesis

Extracellular components

• Plant cells have a cell wall made of cellulose

• Helps maintain shape, prevents water uptake

• Animal cells secrete glycoproteins that function in support, adhesion and movement