CELL STRUCTURE

CELL STRUCTURE

Enormous variety in the size and shape of different cells Smallest cells belong to group of

organismsMycoplasma Only about 0.2 µm in diameter So small that often beyond the limit of

resolution of light microscopes

CELL STRUCTURE

Large cells (giant amoeba)Chaos chaos About 1000 µm in diameter

Larger cellsyolks of bird eggs Single cells containing stored food for the

developing bird

for the most part, cells are between 5 & 50 µm in diameter

CELL STRUCTURE

certain structures are common to most cells plants, animals, and related organisms

have 3 basic structures: cell membrane-outer boundary nucleus-control center cytoplasm-material between the cell membrane

and nucleus

CELL MEMBRANE

all cells are separated from their surroundings by a cell membrane

regulates what enters and leaves the cell aids in the protection and support of the

cell similar to cell walls that surround a house

CELL MEMBRANE

it must communicate with other cells, take in food, and water and eliminate wastes

composed of several kinds of molecules lipids, proteins, cho’s

LIPIDS

• double layer of lipid molecules, known as a ‘bilayer’ forms the basic unit from which cell membranes are constructed

PROTEIN

some proteins stick to the surface of the lipid bilayer, others are free to move around within the bilayer

some act as channels through which molecules can pass

others act like small pumps, actively pushing molecules from one side of the membrane to the other

CARBOHYDRATES

cho’s are attached to proteins or lipids at the membrane surface

many act like chemical id cards, allowing cells to recognize and interact with each other

CELL WALL

in organism such as plants, algae, and some bacteria, the cell membrane is surrounded by a cell wall

helps to protect and support the cell very porouswater, oxygen, carbon

dioxide, and other substances can pass through easily

made up of two or more layers layers form in a series of steps

PRIMARY CELL WALL

1st layer to form develops where two plant cells meet

Contains a gluey substance called pectin, that helps hold the cells together

Each of these cells then forms a primary cell wall on its side of this gluey layer

Made up of cellulose (a fibrous material)

Make the cell wall elasticstretch as it grows

SECONDARY CELL WALL

Plants that have woody stems, another layer secondary cell wall, develops

Composed of cellulose and lignin Lignin makes cellulose more rigid Wood consists mainly of secondary

cell walls

NUCLEUS

Nucleus-info center of the cell Seen in many cells as a large dark

structure 1st described by Robert Brown Not all cells have nuclei Small unicellular organismbacteria and

several other kinds of organisms, do not have nuclei

PROKARYOTES / EUKARYOTES

The absence or presence of a nucleus can be used to divide organisms into two categories:

Prokaryotes-lack nuclei Eukaryotes-contain nuclei

Karyon=nucleus Pro=before Eu=true

PROKARYOTES

Prokaryotic organism Bacteria and their relatives Usually small and unicellular

EUKARYOTES

Eukaryotic organisms Both unicellular and multicellular

NUCLEUS

Nucleus is the information center of the cell

Contains DNA=instructions for making thousands of different molecules

Directs all the activities that occur in a living cell

NUCLEUS

Nuclear envelope Composed of two membranes that form

boundary around nucleus Insidedozens of nuclear pores Molecules move in and out of nucleus through

nuclear pores

NUCLEUS

Nucleolus Most nuclei contain a small region called

nucleolus Made up of RNA and proteins Where ribosomes are made

NUCLEUS

Chromosomes The DNA in the nucleus of eukaryotic cells is

attached to special proteins and forms large structures called chromosomes

Contain genetic information that must be passed to each new generation of cells

CYTOPLASM

Cytoplasm Area between the nucleus and the cell

membrane Contains important structures

TOMORROW

We will discuss the organelles found within the cytoplasm!!!!!!!!!!!!