CH 4 CELL STRUCTURE AND FUNCTION

Discovery of cells

Early scientists had to make their own microscopes

Better microscopes = better knowledge of microscopic life

Robert Hooke Observed cork slides Observed ‘cells’ (like where monks live)

Anton van Leeuwenhoek (10x Hooke’s magnification) Observed algae and ‘animalcules’ (protists)

Other scientists

Mathias Schleiden Plants are made of cells

Theodor Schwann Animals are made of cells

Rudolf Virchow Cells come from other cells

What is the importance of all of these observations?

Cell theory

1. All organisms are made of one or more cells

2. Cells are the basic units of structure and function in an organism

3. Cells come from pre-existing cells

Cell size

Cells come in many shapes and sizes Size of a cell is limited by its surface

area-to-volume ratio As a cell grows, volume increases much

faster than surface area If a cell gets too big, materials entering

and leaving a cell would not be transported fast enough = cell would starve

Cell sizeWorking in pairs, consider two cubes, one with a side

that is 1 cm long and the other with a side that is 6 cm long. For each cube calculate:

1. Surface area (= height × width × number of sides)

2. Volume (= height × width × length)

3. Surface area-to-volume ratio (= surface area:volume)

What pattern do you observe as the size of the cube increases?

What inferences can you make regarding cell size?

Take a few minutes to discuss, and then present your conclusions to the class.

Answers

1. Surface area = 6 cm2 for the first cube and 216 cm2 for the second cube

2. Volume = 1 cm3 for the first cube and 216 cm3 for the second cube

3. Surface area:volume = 6:1 for the first cube and 1:1 for the second cube

As the cube size increases, the surface area to volume ratio decreases.

These calculations show why most cells are small (cells must maintain a large surface area to volume ratio in order to function).

Parts of a cell

PLASMA MEMBRANE aka: Cell membrane Cell’s outer surface Barrier Regulate movement of materials in/out of cell

Cytoplasm: fluid portion of cell Contains all organelles

NUCLEUS Control center Where DNA is located Or floating in cytoplasm

All cells have

these 3 parts.

Two types of cells

Prokaryotes: lack a nucleus and membrane-bound organelles Pro- before Kary- nucleus

Contain a nucleoid: region where DNA is concentrated *not an organelle

Bacteria and Archea

Two types of cells

Eukaryotes: have a nucleus and membrane-bound organelles Eu- true

Organelles: well defined; intracellular bodies that perform specific functions All are enclosed in a

membrane Generally larger than

prokaryotes

Cellular organization

Multicellularity found in more advanced species

Tissue: groups of cells that do a specific job

Organs: tissues that perform a particular job

Organ systems: group of organs that accomplish a related task

Plasma membrane (aka: Cell Membrane)

Location: Surrounds the cell

Functions: Allows only certain molecules to

enter/exit a cell Separates internal metabolism

from external environment Present in ANIMAL & PLANT cells

The “GATE-KEEPER”

Plasma Membrane

Composed of a phospholipid bilayer: double layered membrane of phospholipids

Phospholipids Polar (hydrophillic)

heads – oriented to H2O Nonpolar (hydrophobic)

tails – orient away from H2O

POLAR

NONPOLAR

Membrane components

Many proteins are embedded in plasma membrane

Receptor proteins: recognize and bind to substances outside of cell

Enzymes: assist chem rxns Transport proteins: help substances move

across membrane Fluid mosaic model: phospholipid bilayer

behaves like a fluid more than a solid Lipids and proteins can move around w/in

membrane

Nucleus

Houses and protects genetic information When cell is not dividing, DNA is in

chromatin form Threadlike material

When cell is dividing, DNA is condensed into chromosomes DNA surrounded by proteins

CHROMOSOME

Control Center

Nuclear envelope

Double membrane surrounding nucleus Nucelar pores regulate movement of

materials in/out of nucleus

Nucleolus

Nucleolus: structure inside nucleus Location of ribosomal RNA (rRNA)

synthesis Ribosomes: cell structure responsible

for protein sysnthesis Composed of rRNA

Mitochondria

Double-membraned organelle responsible for energy conversion Organic molecules (glucose + O2) ATP

Inner membrane has many folds cristae More surface area = more ATP

production Have their own DNA Believed to have originated from

prokaryotic cells that were incorporated into ancient eukaryotic cells Symbiotic relationship (both benefit)

Powerhouse

Endoplasmic reticulum (ER)

System of membranous tubes and sacs

2 types Rough (RER):

Attached ribosomes protein synthesis

Smooth (SER): No ribosomes Tubular appearance Lipid and steroids

synthesis

Freeway

Golgi Apparatus

Location: in cytoplasm Function:

package and modify proteins or lipids as they pass them from sac to sac

“address labels” A & P Double membrane

Packaging Center

Lysosomes

Location: in cytoplasm Function:

Contain digestive enzymes to break down macromolecules

WBC’s >> break down bacteria

Autophagy: = digestion of old organelles

Autolysis = Cells broken down by their own lysosomes

A & P Double membrane

Suicide Sacs

Peroxisomes

Location: in cytoplasm (especially in liver and kidney cells)

Function: Similar to lysosomes; contain

different enzymes Neutralize free radicals

(damaging Oxygen ions) Detoxify alcohol and other drugs Produce H2O2 (hydrogen

peroxide) A & P Double membrane

*PROTEIN SYNTHESIS

1. Ribosomes (on Rough ER) make proteins.2. Vesicles transport proteins to Golgi

apparatus.3. Golgi modifies and packages proteins in new

vesicles.4. Vesicles release proteins that are needed

OUTSIDE the cell.5. Vesicles with ENZYMES stay inside the cell as

Lysosomes Peroxisomes Endosomes

CYTOSKELETONMicrotubules

Small hollow tubes anchored near nucleus

Location: cytoplasm Function:

Hold organelles in place Maintain cell shape “tracks” to guide

movement of organelles and molecules within cell

A & P

CYTOSKELETONMicrofilaments

Small threads wrapped around each other

Location: cytoplasm Function:

Cell movement Muscle contraction WBC crawl

A & P

CYTOSKELETONIntermediate Filaments

Location: nucleus & cytoplasm

Function: Anchor nucleus &

some organelles Maintain shape of

nucleus A & P

Cilia & Flagella

Location: surface of cell Function:

Assist in movement CILIA = tiny hairs FLAGELLA = tails

Made of microtubules A & P

Centrioles

Location: cytoplasm Function:

Assist in MITOSIS (cell division)

Made of microtubules A

PLANT CELLSCell Wall

Location: OUTSIDE plasma membrane

Made of CELLULOSE (carbohydrate)

Function: Form rigid wall Helps cells maintain same

shape P Double membrane sometimes

if secondary cell wall forms (i.e. wood)

PLANT CELLSCentral Vacuole

Location: Cytoplasm Function:

Acts as a reservoir for large amounts of water

Also: enzymes, wastes, etc.

When empty, plant wilts.

P Single membrane

PLANT CELLSChloroplasts

Similar to mitochondria Contain own DNA

Location: Cytoplasm Function:

PHOTOSYNTHESIS Light energy converted into

chemical energy (glucose) *Contain green pigment

P Double membrane

PLANT CELLSChromoplasts & other plastids

Location: Cytoplasm Function:

Give color to plants Carrots = orange pigment Daisies = yellow pigment

A & P Double membrane