BiologyCell Structure

& Function

What is a cell?• The smallest unit that is capable of

performing life functions.

• After observing many cells, scientists came up with the cell theory:• All living things are made of 1 or more cells.• Cells are the basic units of structure and

function in organisms.• All cells come from existing cells.

Cell Size•To function efficiently, cells must be small. Why?

• If a cell is the shape of a cube and has 1 mm sides, calculate the surface area of the cube using the formula 6S2. Also, calculate the volume using the formula S3. What is the surface area to volume ratio?

•Do the same calculations for a cell having 2 mm sides.

•What happens to the SA/volume ratio as the cell gets bigger? Why is this bad?

2 Main Cell TypesProkaryotic• Originated approximately

3.5 billion years ago• 0.5- 2µm (µ is the symbol

for “micro” which means 1/1,000,000

• Simple- no nucleus nor other special compartments

• Single, circular DNA molecule

• Example- bacterium

Eukaryotic• Originated approximately 1.5

billion years ago• 2-100µm; typical plant/animal

cell is 10-50µm• Organized- Have a nucleus and

other organelles (structures that carry out specific functions for the cell)

• DNA is in the form of chromosomes

• Example- animal and plant cells

Prokaryotic Bacterial Cell

Eukaryotic Plant Cell

Eukaryotic Animal Cell

Characteristics of ALL CellsAll pro and eukaryotic cells have the following:•Cell membrane- An outer boundary which is also called the plasma membrane•Cytoplasm- The interior of a cell; just the liquid is called cytosol.•Cytoskeleton (microtubules/microfilaments)- Protein filaments (thread-like structures) that are important in cell movement, shape and division•Ribosomes- Structures that do not have a membrane and make proteins •DNA- hereditary information

Eukaryotic Organelles

Organelles that Surround the Cell

• Cell membrane- “Selects” what can enter and leave the cell. More about this later!

• Cell wall– Most commonly found in plant cells and bacteria- NOT IN

ANIMAL CELLS! – Surrounds the cell membrane and provides structure and

support– Made of cellulose- long carbohydrate chain

• Cilia- Short, numerous hairs that move the cell and/or substances outside the cell– What human cells have cilia?

• Flagella- Long tail(s) that moves the cell and/or substances outside the cell– Both cilia and flagella are made of protein

filaments like the cytoskeleton.– What human cell has a flagellum?

Organelles inside the cell• Nucleus

– Directs the cell’s activities– Houses DNA– Houses the nucleolus

• where ribosomes are made

– Surrounded by a double membrane called the nuclear envelope • controls what exits the nucleus like ribosomes

and RNA• has openings called nuclear pores

• Endoplasmic reticulum– System of membranes that move proteins around

inside the cell- “intracellular highway”– Can be smooth or rough

• rough has ribosomes attached to it and smooth does not

• ribosomes can also be found in the cytosol

• Golgi apparatus• Flattened sacs• Processes proteins into vesicles (membrane bound

sacs)

• Mitochondria– Produces ATP- form of energy that can be used by the cell.

What cells of the body have lots of mitochondria?– Has a double membrane

• Outer membrane is smooth and the inner membrane (cristae) is folded.

– Has its own DNA

• Chloroplast– In plants, some protists and some bacteria- NOT IN ANIMAL

CELLS!– Where photosynthesis occurs– Has its own DNA and a double membrane

Mitochondria

Chloroplast

• Lysosome– Spherical organelle where digestion occurs

• Remove the web between fingers of a fetus• Usually in animal cells

• Central Vacuole– Large– Stores water, nutrients and waste– Only in plant cells

• Animal cells have vacuoles- but not central vacuoles

“Typical” Animal Cell

http://web.jjay.cuny.edu/~acarpi/NSC/images/cell.gif

“Typical” Plant Cell

How do animal and plant cells differ?Animal• Spherical• Might have flagella or

cilia

Plant• Rectangular• Have a cell wall• Have chloroplasts• Have a central

vacuole

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Evolution of the Eukaryotic Cell

• A possible explanation for how eukaryotic cells came into existence is the endosymbiotic theory.

• Symbiosis is a relationship between organisms where every member benefits.

• The endosymbiotic theory states that chloroplasts and mitochondria were once prokaryotic bacteria. They entered a larger prokaryotic cell and all parties benefited.

• The chloroplast and mitochondria got extra protection and the larger cell developed the ability to make its own food and energy.

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Evidence of the endosymbiotic theory• Both chloroplasts and mitochondria have

their own circular DNA (like prokaryotic cells).

• Both chloroplasts and mitochondria have a double membrane.

• Mitochondria are approximately the size of bacteria.

Game to Review Organelles