biology 3.2 cell features. the cell theory in 1838, the german botanist mattias schleiden concluded...
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Biology 3.2
Cell Features
The Cell Theory In 1838, the German botanist Mattias
Schleiden concluded that cells make up not only the stems of plants but every part of a plant.
A year later, German zoologist Theodore Schwann determined that cells animals are also made of cells
In 1858, Rudolph Virchow, a German physician, determined that cells came from other cells
Cell Theory The observations of Schleiden,
Schwann, and Virchow form the cell theory which has three parts
All living things are made of one or more cells
Cells are the basic units of structure and function in organisms
All cells arise from existing cells
Cell Size Small cells function more efficiently
than large cells.
Small cells can exchange substances more readily than larger cells because small objects have a higher surface area-to-volume ratio than larger objects
As a result, substances do not need to travel as far to reach the center of a smaller cell
Common Cell Features Al l ce l l s have a ce l l
membrane , an ou te r boundary tha t enc loses the ce l l and separa tes the ce l l i n te r io r, ca l led the cy top lasm, f rom i t ’s su r round ings .
Cell Features The cel l membrane
a lso regulates what enters and leaves the cel l
inc luding gases,
nut r ients,
and wastes
Cell Features
With in the cy top lasm are many s t ruc tu res , o f ten suspended in a sys tem o f m ic roscop ic f ibers ca l led the cy toske le ton
Cell Features Most cel ls have
r ibosomes as wel l
Ribosomes are the cel lu lar s t ructures on which prote ins are made
Cellular Structure
All cells also have DNA
Which provides Instructions for
1. Making proteins
2. Regulates cellular activities
3. Enables cells to reproduce
Features of Cells The smallest and simplest cells are prokaryotes
Prokaryotes are single-celled organisms that lack a nucleus and other internal compartments
Without separate compartments to isolate materials, prokaryotes cells cannot carry out many specialized functions
For nearly two billion years, prokaryotes were the only organisms on Earth
Characteristics of Prokaryotes
Prokaryotes can exist in a broad range of environmental conditions
The cytoplasm of a prokaryotes contains everything inside the cell membrane
A prokaryotes enzymes and ribosomes are free to move around in the cytoplasm because there are no internal structures that divide the cell into compartments
Prokaryotes In prokaryotes, the genetic material is a single circular
molecule of DNA
Prokaryotic cells have a cell wall surrounding the cell membrane that provides structure and support
Prokaryotes lack an
Internal support skeleton so
They rely on a strong cell
wall to give the cell shape
Prokaryotes Some prokaryotes cell walls are surrounded by a structure
called a capsule. The capsule enables the prokaryotes to cling to almost anything; teeth, skin, food, etc.
Many prokaryotes have flagella which are long, threadlike structures that protrude from the cell’s surface and enable movement
Prokaryotic flagella rotate
propelling the organism up
to 20 cell lengths per second
Eukaryotic cells
The first cells with compartments were primitive eukaryotic cells which evolved about 2.5 billion years ago
A eukaryote is an organism whose cells have a nucleus
The nucleus is an internal compartment that houses the cell’s DNA
Eukaryotic cells
Other internal compartments, or
organelles, enable eukaryotic
cells to function in ways
different from prokaryotes
An organelle is a structure that carries out specific activities in the cell
A complex system of internal membranes connects some organelles within the cytoplasm
Eukaryotic cellsThese membranes provide channels
that guide the distribution of substances within the cell
Many single celled eukaryotes use flagella for movement
Short hairlike structures called cilia protrude from the surface of many eukaryotic cells
Flagella or cilia propel some cells through their environment
In other cells, cilia or flagella move substances across the cell’s surface
Eukaryotic cells
A web of protein fibers makes up the cytoskeleton
The cytoskeleton holds the cell together and keeps cell membranes from collapsing
Cytoskeleton The cytoskeleton provides the
internal framework of an animal cell much like our skeletons provide our internal framework
The cytoskeleton is composed of an intricate network of protein fibers anchored to the inside of the plasma membrane
Cytoskeleton By linking one region to another,
they support the shape of the cell, much as steel beams anchor the sides of a building together
Other fibers attach the nucleus and other organelles to fixed locations in the cell
Because protein fibers are too small for a light microscope to reveal, biologists visualize the cytoskeleton by attaching flourescent dyes to antibodies.
Cytoskeleton There are three types of
cytoskeleton fibersLong slender
microfilaments made of the protein actin
Hollow tubes called microtubules made of the protein tubulin
Thick ropes of protein called intermediate fibers
CytoskeletonThe actin fibers of the
cytoskeleton form a network just beneath the cell surface that is anchored to membrane proteins embedded within the cell membrane
By contracting or expanding, actin plays a major role in determining the shape of animal cells by pulling the plasma membrane in some places and pushing it out in others
CytoskeletonMicrotubules within the
cytoskeleton act as a highway system for the transportation of information from the nucleus to different parts of the cell
RNA molecules are transported along microtubular “rails” that extend through the interior of the cell like train tracks
CytoskeletonIntermediate Fibers of the
cytoskeleton provide a frame on which ribosomes and enzymes can be confined to particular regions of the cell
The cell can organize complex metabolic activities efficiently by anchoring particular enzymes near one another
The Cell Membrane The cytoplasm of a cell is
contained by it’s membrane
Cell membranes are not rigid like an eggshell but fluid like a soap bubble
The fluidity of a cell membrane is caused by lipids
Lipids form a barrier that separates inside the cell from outside the cell
The Cell Membrane This barrier only allows certain
substances to pass through in or out
This ability to control what enters or leaves the cell is caused by the way phospholipids interact with water
A phospholipid is a lipid made of a phosphate group and two fatty acids
The Cell Membrane As shown at right, a
phospholipid has both a polar “head” and two nonpolar “tails”
The head of a phospholid is polar and is attracted to water.
In contrast, the two fatty acids, the “tails” are nonpolar and therefore they are repelled by water
The Cell Membrane In a cell membrane, the
phospholipids are arranged in a double layer called a lipid bilayer
The lipid bilayer allows lipids and substances that dissolve in lipids to pass through
Member Proteins Various proteins are
located in the lipid bilayer of a cell membrane
The motion and fluidity of phospholipids enables some membrane proteins to move around within the lipid bilayer
Member ProteinsCell membranes contain different types of
proteins, among them
marker proteins which attach to carbohydrates
Receptor proteins bind specific substances
Enzymes embedded in the cell membrane are involved in biochemical reactions within the cell
Transport proteins aid the movement of substances into and out of the cell