Cell Features

Section 3-2

What is the Cell Theory?

All living things are made of one or more cells.

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

All cells arise from other living cells.

Remember from Section 3-1 the scientists that contributed to development of the cell theory – Virchow, van Leeuwenhoek, Schwann, Schleiden, and Hooke

Surface Area – to Volume Ratio Small cells function more efficiently

than larger cells Human body cells range from 5-20 μm All substances that enter or leave a cell

must cross the cell’s surface. If the cell’s surface to volume ratio is too low, the substance cannot enter or leave the cell in numbers large enough to meet the cell’s needs.

Surface Area – to Volume Ratio (con’t) Small cells can exchange substances

more readily than large cells because small objects have higher surface area to volume ratio than larger objects.

The result is substances do not need to travel as far to reach the center of a small cell.

Common Cell Features

1) Cell Membranea. Outer boundary of cellb. Encloses cell interior from cell’s

surroundingsc. Regulates what enters and leaves cell

2) Cytoplasma. The cell’s interior contentsb. Made of various membrane covered

organelles and the cytosolc. Cytosol – soluble portion of cytoplasm;

includes small molecules and small particles.

Common Cell Features (con’t) 3) Cytoskeleton

a. Cytoplasmic network of protein filaments that plays an essential role in cell movement, shape, and division

4) Ribosomesa. Cellular structures on which proteins are made

5) DNA (deoxyribonucleic acid)a. Provides instructions for making proteinsb. Regulates cellular activitiesc. Enables a cell to reproduce

Prokaryotes The smallest and simplest cells – informally

called bacteria Single-celled organism that lacks a true

nucleus and other internal compartments. Because of this, they cannot carry out many specialized functions.

Size ranges from 1 to 15 μm Can exist in a broad range of environments Cytoplasm contains everything inside the cell

membrane Have no internal structures dividing cell into

compartments – ribosomes move freely in cell

Prokaryotes (con’t) Have circular DNA that is suspended in

cytoplasm; no nuclear membrane – NO TRUE NUCLEUS!!!

Cell Wall – surrounds cell membrane; provides structure and support needed because no cytoskeleton; made of polysaccharides connected by short strands of amino acids

Some cell walls are surrounded by capsules. Capsules are made of polysaccharides. These capsules allow bacteria to cling to almost anything.

Prokaryotes (con’t)

Flagella Long, thread-like structures that protrude

from the cell’s surface Enable movement Rotate and propel bacteria through its

environment at speeds of up to 20 cell lengths per second

Eukaryotes Organism that has a true nucleus –

surrounded by nuclear membrane Have internal compartments –

organelles – structures that carry out specific activities in the cell

Nucleus – internal compartment that houses the cell’s DNA

Organelles enable eukaryotic cells to function in ways different from bacteria

Range from single-celled to multicellular

Eukaryotes (con’t) Some have flagella; others have cilia protruding

from surface. Cilia – hair-like structures that can either propel the cell or can move substances across the cell’s surface.

Cytoplasm – includes everything inside the cell membrane, but outside the nucleus

Cytoskeleton – web of protein fibers that hold cell together and keep cell membrane from collapsing or folding. Microtubules – long, hollow tubes that extend

through the cytoplasm, supporting the cell Microfilaments – extremely thin protein strands

that also support cell’s shape and structure

Eukaryotes (con’t)

Ribosomes – moving freely in cell or attached to the rough endoplasmic reticulum

Cell membrane – contains cytoplasm and organelles

Cell Membrane Fluid (like a soap bubble), not rigid.

This is caused by lipids. The lipids form a barrier that separates the

inside of the cell from the outside of the cell and only allows certain substances to pass through – SELECTIVELY PERMEABLE!!!

Barrier Selective permeability caused by the way the

phospholipids interact with water Phospholipid – lipid made of phosphate group

and two nonpolar fatty acid tails which make up the interior of the cell membrane/lipid bilayer.

Cell Membrane (con’t) Forced to inside of bilayer because of interaction

with water. Water on both sides of cell Ions and most polar molecules (sugars and some

proteins) are repelled by the nonpolar interior. Proteins are embedded in the cell membrane

Nonpolar part of membrane protein attracted to interior of the lipid bilayer, but repelled by water on either side.

Polar part of membrane protein attracted to water on either side of lipid bilayer

Dual attraction holds protein in lipid bilayer Can move around because of fluidity of membrane

Cell Membrane (con’t)

Different Types of Membrane Proteins1. Marker Protein – attached to a

carbohydrate on cell’s surface to identify the cell type

2. Receptor Protein – recognizes and binds to specific substances

3. Enzymes – involved in important biochemical reactions in the cell

4. Transport Proteins – aid in movement of substances in and out of the cell