Cell Structure and Function

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Prokaryotic Cells

1. Prokaryotes: Do not have nucleus but they DO have DNAa. Smallest and simplest cellsb. DNA located in cytoplasm

(nucleoid region)c. Have cell wallsd. Have ribosomese. Many have flagella for

movementf. NEVER multicellular

2. Bacteria have prokaryotic cells

Slide # 3

Bacteria are the only organisms that have

prokaryotic cells.

DNACytoplasm

Cell wall

Cell membrane

ribosomesflagellum

Eukaryotic Cells

1.Eukaryotic: cells that have nucleus

2. Have specialized structuresa.Larger & more complex

than prokaryotic cells3. Unicellular & multicellular

organisms have eukaryotic cells

Slide # 3 nucleus

mitochondria

nucleoluschloroplast

vacuole

Cell membrane

Cell wall

Cellular Structures

Structure and Functions of the Nucleus

1. Nuclear membrane is a double membrane (each is a lipid bi-layer) pourous (controls what enters / exits nucleus

2. Nucleolus produces ribosomes

3. DNA is organized into distinct units called chromosomes that carries the genetic material

Nucleus controls cell’s activities because it contains the cell’s DNA

Endoplasmic Reticulum (ER)

1. A network of membranous tubules and sacs (cisternae)

2. ER membrane is continuous with the nuclear membrane

3. Transports substances throughout the cell

4. Rough ER

* has ribosomes

* produces proteins (pancreas produces insulin)

*makes membrane proteins

Smooth ER * no ribosomes * makes lipids & steroid hormones * breaks down toxins in liver cells * controls release of calcium in muscle cells

Golgi Apparatus (Body) (Complex)1. Single membrane

2. Membrane covered sacs (5-8 layers)

3. Receives products from ER

4. Modifies products from ER

5. Packages products into vesicles

6. Sorts and targets products to different parts of the cell or to be exported from the cell

Hydrolytic enzymes & lysosomal membranes that are made by the rough ER are packaged into lysosomes by the Golgi

Ribosomes (Free & Attached)

1. NOT membrane bound

* found in prokaryotes & eukaryotes

2. Proteins are synthesized (made) here

3. Free Ribosomes:

* found throughout the cytoplasm

* make proteins that function in the cytoplasm

4. Attached ribosomes (on ER) make proteins that are:

* destined for insertion into membranes

* put into lysosomes * many are exported

from the cell

Lysosomes1. Single membrane

2. Contain hydrolytic enzymes that break down cell waste & “junk” from outside the cell into simple compounds

* simple compounds transferred to cytoplasm as new cell building materials

3. Lysosomes originate in the Golgi

but enzymes are made in rough ER

4. Most numerous in disease fighting

cells (white blood cells) that engulf bacteria by phagocytosis

Tay Sachs is a genetic disorder that prevents the formation of the enzyme that breaks down ganglioside (a lipid). Result is damage to nervous system, mental retardation, and death in early childhood.

Mitochondria

1. Found in cytoplasm of ALL eukaryotic cells

* number of mitochondria in the celldepends on the cell & its function

2. convert oxygen and nutrients into ATP (adenosine triphosphate) through aerobic respiration (metabolism)

* ATP is the energy that cells use

3. Has its own DNA

4. Can reproduce independently of the cell

Cytoskeleton

1. Made up almost entirely of protein filaments

2. Functions:

* give cell shape

* provides mechanical strength

* aids in locomotion (especially in Amoeba and white blood cells -- pseudopods)

* helps in separating chromosomes during mitosis

* anchors organelles in cytoplasm

Vacuoles

1. Both plant and animal cells have vacuoles

* Temporary structure in animal cells

* Large, permanent structure in plant cells

2. Function: Stores water

3. When filled with water:

* helps cell maintain shape by exerting pressure on cell membrane & thus cell wall

* When plants wilt, they have lost water from vacuole

Large, central vacuole

Plastids1. Found in plant cells

2. Have a double membrane

3. Many different types

* chromoplasts

-- found in brightly colored flowers & fruits & leaves

-- have accessory pigments involved in photosynthesis

* amyloplasts

-- found in root cells; store starch

* leukoplasts (colorless)

-- contain oils and lipids

Chromoplasts

Amyloplasts

Chloroplasts1. Double membrane2. Plastids that convert light energy into

chemical energy (photosynthesis) * found in leaves & green stems3. Addition membrane system inside

the chloroplast * Thylakoids; flattened sacs * Grana; stacks of thylakoids * thylakoids are surrounded by fluid

called stroma4. Stroma contains circular DNA,

ribosomes, and enzymes5. Can replicate on own by binary

fission

Chlorophyll is found inside the thylakoids

Plasma (Cell) MembraneThe Boundary

1. Described as a lipid bi-layer fluid mosaic model2. Fatty acid tails face each other (hydrophobic)3. Phosphate heads (hydrophilic) are on the inside and outside of the membrane4. Lipid portion: isolates hydrophilic

substances from entering / exiting the cell

5. Protein portion: allows hydrophilic molecules and ions (charged) in / out of cell & communicates with other cells

Phosphate headhydrophilic

Fatty Acid tailshydrophobic

proteins

Membrane Structures / Functions

1. Transport: provides a hydrophilic channel across the membrane that is selective to a particular particle (salt, sugars, water, etc)

2. Some transport proteins change their shape to move substances from one side to another

hydrophilic

Changes shape

Cell Wall

1. Found in plant cells (NOT animals)

2. Protects cell, maintains cell shape, & prevents excessive uptake of water

3. Cellulose in cell wall – cross linked structure (like a chain linked fence) – makes cell wall very strong

Theory of Endosymbiosis

1. Theory that Eukaryotes arose from symbiotic relationship between prokaryotes and aerobic bacteria that they took in

2. 2 organelles involved: mitochondria & chloroplasts

3. Evidence that supports theory:

* bacteria, mitochondria, & chloroplasts all have circular DNA

* bacteria, mitochondria, & chloroplasts all about the same size

* bacteria, mitochondria, & chloroplasts can self replicate by binary fission

Prokaryote takes in aerobic bacterium

Prokaryote takes in cyano bacterium (capable of photosynthesis)

Contractile Vacuoles

1. Found in animal-like PROTISTS, not plants or animals

2. Pump excess water out of cell; keeps them from bursting open

Diffusion through phospholipid bilayer

What molecules can get through directly?

– fats & other lipids

inside cell

outside cell

lipid

salt

aa H2Osugar

NH3

What molecules can NOT get through directly?

– polar molecules

• H2O

– ions (charged)• salts, ammonia

– large molecules• starches, proteins

Animal Cells Plant Cells

Several small vacuoles scattered throughout the cell

Cell membraneRibosomesNucleusEndoplasmic reticulumGolgi apparatusVacuolesMitochondria

Cell WallChloroplast1 Large central vacuole

Slide # 10

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Structures in Animal verses Plant Cells