Cell Biology

Part 2

Cytoskeleton

Network of protein fibers and in the cytoplasm.

Functions

• Cell structure and shape.

• Cell movement.

• Cell division - helps build cell walls and move the chromosomes apart.

Components of the CytoskeletonOrganized in deceasing diameter

• Microtubules

• Microfilaments

• Intermediate Filaments

Microtubules

• Structure - small hollow tubes made of the protein “tubulin”.

• Size - 25 nm outer diameter with a 15 nm inner diameter. Can be 200 nm to 25 m in length.

Microtubules

• Found in the “spindle” apparatus (during cell division), cilia, flagella, basal bodies and centrioles.

Functions

• Maintenance of cell shape.

• Hold organelles in place.

Microfilaments

• 5 to 7 nm in diameter.

• Structure – made up of the protein “actin”

Functions• Muscle contractions.• Cytoplasmic streaming. • Pseudopodia (amoeboid movement)

found in amoebae and phagocytes (white blood cells).

• Cleavage furrow formation.• Maintenance and changes in cell

shape.

Microfilaments are stained green.

Cilia and FlagellaClassified by their lengths and numbers

• Cilia - short, but numerous.

• Flagella - long, but few.

• Function - to move cells or to sweep materials past a cell.

Cilia and Flagella

• Structure - 9+2 arrangement of microtubules, covered by a plasma membrane

(different in bacteria)• Made of contractile proteins• Uses ATP

Centrioles and Basal Bodies

act as “microtubule

organizing centers”

or MTOC’s

Centrioles

• Usually one pair per cell, located close to the nucleus.

• Found in animal cells only.

• 9 sets of triplet microtubules.

• Help in cell division.

Basal Bodies

• Same structure as a centriole.

• Found at the base of the cilia and flagella.

Plant Cells

Plant Cell

Cell Wall

• Nonliving jacket that surrounds some cells.

• Found in:–Plants–Prokaryotes–Fungi–Some Protists

Plant Cell Walls

• All plant cells have a Primary Cell Wall.

• Some cells will develop a Secondary Cell Wall.

Cell Walls

• Plant cell walls are made of cellulose ( a polysaccharide made of -glucose).• Fungi cell walls are made of chitin (a

polysaccharide)• Function as the cell's exoskeleton for

support and protection.

Middle Lamella

• Thin layer rich in pectin (used to make jelly) found between adjacent plant cells.

• Glues cells together.

Vacuoles and VesiclesFluid-filled, membrane-bound bodies

5 Types of Vacuoles and Vesicles

• Transport vesicles

• Food vacuoles

• Storage vacuoles

• Central vacuoles

• Contractile vacuoles

The function of the vacuole depends on the organism.

In ProtistsProtists (single-cell organisms)

• “Food” vacuoles store newly ingested food until the lysosomes

can digest it.• “Contractile” vacuoles pump out

excess water.

Contractile Vacuole

Contractile Vacuole

Food Vacuoles

Central Water Vacuole

• Large single vacuole when mature making up to 90% of

the cell's volume.

Function of Central Water Vacuole

• Water regulation.• Storage of ions.• Storage of hydrophilic

pigments. (e.g. red and blues in flower petals).

Other vacuoles and vesicles• Storage vacuoles in plants store

starch, pigments and toxic substances (such as nicotine)

• Transport vesicles move materials from one organelle to another, or from organelle to the plasma membrane. (“exocytic vesicles” move materials to the plasma membrane for export, “endocytic vesicles” transport materials from outside the cell to the plasma membrane to be imported)

Chloroplasts

• Contain DNA.• Can reproduce themselves.• Often contain starch.• May have been independent

cells at one time.

Function of Chloroplasts

• Photosynthesis - chloroplasts use of light energy to make food. (sugars)

• Contain the green pigment chlorophyll.

Chloroplasts

Enzymes in a crystal

Chromoplasts store plant pigments such as chlorophyll,

carotene.

• Found in plants only.• Classified (named) by color example:

Chloro means green, therefore a chloroplast is a green plastid that stores chlorophyll

• Leuco means white, therefore Leucoplasts (AKA Amyloplasts) are white plastids that store starch.

ComparingPlant Cells and Animal Cells

Plant Cells Have cell walls,

chloroplasts, and central water

vacuoles…animal cells do not!!

Animal CellsHave lysosomes and centrioles….

Plant cells do not!!