Chapter 7: Cell Structure

Section 1: Introduction to Cells

I. Cells – the smallest unit of life; all living things are made of one or more cells

A. Robert Hooke – English monk in 1665; observed cork under a microscope & saw “little boxes”. Named these “boxes” cells after the rooms monks lived in.

B. Anton van Leeuwenhoek – Dutch 1673; first to observe living cells

II. Cell TheoryA. Evidence for Cell Theory:

1. Matthias Schleiden – proposed all plants are made of cells

2. Theodor Schwann – proposed all animals are made of cells

3. Rudolf Virchow – proposed all cells come from other (preexisting) cells

B. Three Components of cell theory:1. All living things are made of one or more cells.2. Cells are the basic unit of structure & function

in an organism.3. Cells only come from the reproduction of

other living cells.C. Modern Cell Theory also includes:

A. Energy flow occurs within cellsB. Heredity information (DNA) is passed on from

cell to cellC. All cells have the same basic chemical

composition

III. Cell DiversityA. Looking at cells

1. Size – range from microscopic to visisble with naked eye.• Limited by a cell’s surface area-to-volume

ratio• If cell is too large, it takes too long for

materials to travel through it2. Shape – spheres, cubes, flat, have extensions

(branched), smooth or rough surfaces.

Examples of Cell Shapes

IV. Cell Features A. Internal Organization = how the inside is

divided into regions/areas for specific functions.

1. Cell Membrane – cell’s outer boundary2. Cytoplasm – fluid cytosol & any cellular

structures suspended in cytosol

3. Nucleus – cellular structure that houses DNA4. Organelles – membrane-bound cellular

structures that carry out specific functions in a cell

B. Types of Cells1. Eukaryotes – cells with membrane-bound

organelles & nucleus2. Prokaryotes – lack membrane-bound

organelles & nucleus

Section 2: Inside the Eukaryotic Cell

I. Cell Membrane – outer layer that surrounds the cell that allows nutrients & wastes in and out of the cell

A. Selectively Permeable – some materials are allowed through, either in or out of the cell

B. Made of .1. Due to the make up of the cell membrane, only

certain materials can pass through it.

II. Cytoplasm – gelatin-like aqueous fluid (cytosol) & the organelles suspended in it

1. Vesicle – small, spherical membrane sac that transports proteins

III. Directing Cell ActivityA. Nucleus – “brain” of the cell; directs all cell

activities, cell division, & the making of proteins (DNA is stored here)

1. Nuclear Envelope – double membrane around nucleus; has pores (holes) that allow certain molecules in or out

2. Nucleolus – spherical area inside the nucleus that makes RNA & ribosome parts.

B. Ribosomes – made of RNA & proteins1. Makes proteins2. Can find them floating free in the cytoplasm

(“free”) or attached to the E.R. (bound).

IV. Protein Processing Organelles

A. Endoplasmic Reticulum – system of internal membranes

1. Rough E.R. – covered with ribosomes; aids ribosomes in making proteins & transporting them by making vesicles

2. Smooth E.R. – not covered with ribosomes; makes steroids, breaks down toxins, & regulates calcium levels

B. Golgi Apparatus – system of flattened membranes

1. Modifies, packages, and secretes different molecules in vesicles.

2. Assists E.R. in modifying proteins that are leaving the cell.

V. Energy Production Organelle

A. Mitochondria – “power house of the cell”1. Makes ATP!2. Has a 2nd, inner membrane that has folds

called cristae.3. Has its own DNA.

VI. Other Organelles

A. Lysosomes – contains enzymes that digests proteins, DNA/RNA, old organelles, bacteria, etc.

B. Vacuoles – can help maintain water concentrations, store food, etc.

C. Cillia & Flagella – both help move the cell1. Cillia are tiny hairlike projections.2. Flagella is a single long whip-like tail

VII. Framework of the Cell

A. Cytoskeleton – web of protein fibers that supports the cell & its organelles

1. Microfilaments – long thin fibers of the protein actin; pulls the membrane in & out in some places

2. Microtubules – thick hollow fibers of the protein tubulin; molecules move through it

3. Intermediate Fibers – moderately thick & anchors organelles in place

VIII. Plant Cells – have some organelles not present in animal cells

A. Cell Wall – rigid, inorganic layer surrounding the cell membrane; made of cellulose & other carbohydrates

B. Central Vacuoles 1. Fluid-filled organelles that store water, ions,

enzymes, & wastes2. Can take up 90% of the space/volume of a cell

C. Chloroplasts 1. Have two membranes & their own DNA2. Absorb sun light & converts it to food

(photosynthesis)

Plant Cell

Animal Cell

Section 3: From Cell to OrganismI. Diversity in Cells

A. Prokaryotes – cells that lack membrane-bound organelles & nucleus

1. Vary in shape, how they obtain food & use energy, makeup of the cell wall, & how they move.

2. Flagella3. Pili – short, thick outgrowths; attach

prokaryote to surfaces or other cells

Prokaryote Cell

B. Eukaryotes – cells with membrane-bound organelles & nucleus

1. Animal vs. Plant Cells

2. Eukaryote cells vary in internal makeup so that cells can become specialized for certain functions

i. Muscle cells use large amount of energy, so they contain many mitochondria!

Animal Cells Plant CellsLysosomes Central VacuoleFlagella Cell WallVesiclesCentrioles

Chloroplast

II. Levels of Organization

Cells Tissues Organs Organ System Organism

A. Tissues – group of cells that have similar structures & functions

1. Muscle tissue, bone tissue, vascular tissue in plants

B. Organs – different tissues arranged together to perform a specific function

1. Heart, lung, leaf

C. Organ System – group of organs that work together to perform a set of functions, or a major body function

1. Circulatory system, shoot systems of plants

D. Organism – interaction of all organ systems to carry out all life processes

1. Human, Oak tree

Levels of Organization

III. Body Types

A. Unicellular – entire body of an organism is one cell

B. Colonial – cells that live as a connected group but do not depend on each other for survival

C. Multicellular – cells are specialized to perform one or a few functions of life

1. Differentiation – process by which cells develop specialized forms & functions

2. Life depends on the interaction of all the cells!

Unicellular, Colonial, & Multicellular