cell structure and function. the biological universe consists of two types of cells: 1. prokaryotic...
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Cell Structure and FunctionCell Structure and Function
The biological universe consists of two types of cells:
1. Prokaryotic cells 2. Eukaryotic cells
Prokaryotic Cells:Prokaryotic Cells:
Single celled organismsSimple internal organizationLack a defined nucleus Less than 1 micrometer in diameter
A Prokaryotic CellA Prokaryotic Cell
Cell Wall: Offers protection for the cell. Composed of carbohydrate-
protein complex called Peptidoglycan.
Plasma Membrane: Found on inside of cell wall. Responsible for the passing of
various nutrients across the membrane.
Capsule: Cell may have additional
carbohydrate layer that disables it from interacting with various surfaces
Pili: Extensions that are longer than
Cilia Mainly used for Sexual
reproduction with other bacteria.
DNA is exchanged via pili. Not all bacteria have piliCilia: May contain cilia. Used to
swipe molecules towards the cell for endocytosis.
Flagella: May Contain Flagella. Longer than Pili Used for motility
Ribosomes:Ribosomes: Most ribosomes
(protein synthesizing particles) are found in the DNA free region of the cell.
Site of Protein Synthesis
Appear Granular on images
Nucleoid RegionNucleoid Region
The Genetic material (DNA) is found in a single circular DNA molecule that is folded back on itself many times in the central region of the cell. It appears as a dark dense mass in the center of the cell.
It may contain small circular, independent units of DNA called Plasmids.
– May contribute in ability to adapt to rare environments.
– Used in biotechnology (See genetics – Topic 4)
Mesosome– Infolding of the plasma
membrane to assist in compartmentalization (ex. Enzymes can be found here)
Most prokaryotes studied in Most prokaryotes studied in laboratories are bacteria.laboratories are bacteria.
I.e.– Escherichia Coli (E.
Coli) found in animal intestine
Cyanobacteria (Previously known as Blue-green Algae)
Binary Fission Binary Fission Bacteria go through binary
fission as a method of reproduction (Asexual Reproduction)
Steps involved: DNA is copied Separation of DNA
molecules toward two ends of cell
Elongation of cell Division of cytoplasm and
plasma membrane Microtubules help separate
DNA. It is a protein called FtsZ
Eukaryotic Cells:Eukaryotic Cells:
Includes all members of plant and animal kingdoms
Surrounded by a plasma membrane that separates it from the external environment
Range from 5-100 micrometers Internal membranes enclose specific
compartments, organelles and separates them from the rest of the cytoplasm (Region of cell lying outside the nucleus.)
Largest organelle in Eukaryotic cell is the nucleus. It is a membrane bound organelle and holds most of the cellular DNA.
Other organelles present in nearly all eukaryotic cells:
1. Mitochondria – responsible for cells energy metabolism
2. Rough and smooth endoplasmic reticulum – network of membranes in which certain proteins and lipids are synthesized.
3. Golgi Vesicles – Direct membrane components to appropriate places in the cell.
4. Peroxisomes – Fatty acids and amino acids are degraded.
5. Lysosomes - Animal cells, not plant cells - Degrade worn-out cell constituents and foreign
materials taken in by the cell
6. Chloroplasts – Plant cells and certain single celled organisms
7. Vacuoles
- plant and some single celled eukaryotes
- large fluid filled organelles
- store nutrients and waste compounds
8. DNA in nucleus – packaged into linear
structures called chromosomes
The Cell Membrane and The The Cell Membrane and The Fluid Mosaic Membrane Fluid Mosaic Membrane
ModelModel A phospholipid
molecule contains:
1. 2 fatty acid chains 2. Glycerol backbone.
The head of the molecule is Polar and Hydrophilic
The tail of the molecule is
non-polar and hydrophobic.
A molecule that is both hydrophilic and hydrophobic is called AMPHIPATHIC.
What happens when phospholipids What happens when phospholipids are put in water…are put in water…
Attraction and repulsion of polar head group and non-polar tail group, respectively.
Forming a spontaneous
spherical bilayer – Hydrophilic heads
facing the outside Hydrophobic tails
facing eachother
The Cell MembraneThe Cell Membrane
The cell membrane is composed of a phospholipid bilayer.
There are also other components within the bilayer:– Proteins – Glycoproteins– Glycolipids– Cholesterol
The Fluid-Mosaic Membrane The Fluid-Mosaic Membrane ModelModel
Phospholipid molecules and proteins that are embedded in the membrane tend to drift sideways. This supports the idea of the cell membrane having a Fluid Consistency.
In the cell membrane we find:In the cell membrane we find:
ProteinsCarbohydrates Cholesterol
Why do we need these components in the
cell membrane?
ProteinsProteinsThere are two types of membrane proteins:There are two types of membrane proteins:
1. Peripheral or Extrinsic Proteins
They do not interact with hydrophobic core of phospholipid bilayer.
Bound to polar head of the phospholipid orBound to the integral or intrinsic proteins
2. Integral or Intrinsic Proteins
Embedded in the phospholipid bilayer They can be :
Transmembrane (Span the entire phopholipid bilayer)
Lipid-anchored (Anchored to one of the phospholipid layers)
Function:Function:
On the Extracellular surface
1. Cell-cell signaling 2. Cell surface receptors
(I.e. Hormones use these receptors to transmit messages into the cell)
Within the Membrane
1. Proteins form channels and pores to move molecules across the membrane
On the Cytosolic Face of membrane
1. Proteins anchor
cytoskeletal proteins that support the membrane and send signals to various parts of the cell.
CarbohydratesCarbohydrates
Are found bound to either
Proteins – called glycoproteinsLipids – called glycolipids
Purpose:
1. They help increase hydrophilic character of lipids and proteins
2. Stabilize conformation (or shape) of many membrane proteins.
CholesterolCholesterol
Generally, the cell membrane is – Fluid-like– And has drastic changes in physical properties
over a very narrow temperature range:
High temperature – Very Fluid Low temperature – Gel-like
This steroid sits between the phospholipid tails of the bilayer.
Cholesterol maintains the favored fluid-like consistency.
How does cholesterol How does cholesterol maintain the fluid-like maintain the fluid-like
consistency?consistency? 1. At higher temperatures, cholesterol
makes the membranes less fluid by making the fatty acid chains less mobile
2. At lower temperatures, cholesterol keeps membranes fluid by preventing the fatty acid chains of the phospholipid from binding to one another.
Recap of New termsRecap of New terms::
1. Peripheral or Extrinsic Proteins 2. Integral or Intrinsic Proteins
– Transmembrane– Lipid-anchored
3. Extracellular surface 4. Cytosolic Face 5. Glycoproteins 6. Glycolipids 7. Fluid-like 8. Gel-like
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