The cell: Structure and Function
Cell- Smallest unit that can carry on all the process of life.
Unicellular- One celled organisms ( paramecia, bacteria, amoeba).
Multicellular- made of many individual cells.
History of Cytology
(Study of Cells)
Began with the invention of microscope in the 1600’s.
Robert Hooke- English Scientist in 1665 was first to observe cells under
microscope. Observed dead cork cells. Gave them the name “cells’ since they
looked like little boxes or rooms in a prison.
Anton van Leeuwenhoek
Dutch microscope maker, and was the first to observe living cells in 1675.
The Cell Theory
This theory was developed 150 years after Hooke and Leeuwenhoek.
Matthias Schleiden- German botanist who in 1838 proclaimed “All plants are
composed of cells.”
Theodor Schwann- German zoologist who in 1839 proclaimed “ All animals
are composed of cells.”
Rudolph Virchow-
German Physician who in 1855 proclaimed “ Cells come
from only pre-existing cells.”
These 3 observations together form the Cell Theory.
1. All living things are composed of one or more cells.
2. Cells are organisms and the basic units of structure and function
3. Cells come only from existing cells.
Microscopes
Why were the early microscopes limited in there magnification power?
The diffraction or scattering of light makes it harder to pass
through the specimen.
Scanning Electron Microscope
Scanning Tunneling Microscope
Transmission Electron Microscope
(Flagellum)
Cell Diversity
Not all cells are a like, they differ in size, shape and internal organization.
Size- 10-50 Micrometers(um) in diameter and are visible only with a
microscope. Most can’t get much larger due to their surface area
becoming too small in relation to the interior of the cell to carry on life
functions.
Shape- Most cells are cuboidal(box shaped) or spherical(ball shaped).
Some cells differentiate because of their functions.
1. Nerve cell- long extensions allow it to receive and transmit nerve impulses.
2. Skin cells- flat, overlap with others to cover body surface. Ex: House shingles
3. White blood cells- change shape to fit into openings in blood vessels to
engulf bacteria, viruses, and fungi invading tissues.
Internal Organization of the cell
Organelles- “little organ” structures that perform specific functions for the cell,
enclosed by membranes. Organelles are to a cell as organs are to the body.
Nucleus- Large structure near the center of the cell, contains DNA, controls the
activities of the cell. When cell divides DNA condenses in chromosomes
Prokaryotes- cells that lack a nucleus and membrane bound organelles. Have 2
domains Bacteria and Archaea
Pro- means “before”
Eukaryotes- cells with a true nucleus and membrane bound organelles.
Eu- Means “True”
SEM-Endoplasmic Reticulum
Three main parts of Eukaryotic cell:
1. Cell Membrane- the outer boundary of the cell
2. Cytoplasm- Inside cell membrane, contains water, salts, and organelles
3. Nucleus- contains DNA and directs activities of the cell
EX: Plants, Animals, Fungi, Protists
CELL ORGANIZATION
• Colonial organism- collection of genetically identical
cells that form a connected group
• Tissue groups of cells that carry out specific functions
• Organs- groups of tissues that perform jobs in the
organism
• Organ system- group of organs that accomplish
related tasks
Cells
Tissue
Organ
Organsystem
Cell or Plasma Membrane
Thin membrane, gives shape, support and flexibility to the cell.
Selective Permeable Membrane- Thin membrane that regulates what molecules
enter and leave the cell. ( Like bouncers or guards at the door)
Lipid Bilayer- 2 layers of lipids (fatty acids).Lipids, Carbohydrates and proteins
make up this layer. It layers Hydrocarbon “tails” face the inside of the layer,
while the Carboxyl “heads” face the outside toward the aqueous solution.
Hydrocarbon tails are Hydrophobic. “Water Fearing”
Carboxyl heads are- Hydrophilic. “ Water Loving”
Proteins are also in bedded in this layer, and with proteins are able to move
across membrane and change their positions.
This is called the Fluid Mosaic Model.
Cytoplasm and Organelles
Cytoplasm- jelly like material inside cell membrane that contains organelles, water,
salts, and organic molecule; it is in constant motion(Fluid like the membrane).
Cytosol- part of cytoplasm that contains molecules and small particles, it is made of
20% proteins
Cytoplasmic Streaming- this is the constant motion of the cytoplasm.
Organelles- “little organs” each organ has a specific function in the cell.
a) ribosomes- most numerous organelles, specific site of protein synthesis, very
small spherical organelles.
Mitochondria- tiny organelles transfer energy from organic molecules to ATP and it
powers most of chemical reactions
Proteins that are synthesized for use in the cell are produced by free floating
ribosomes.
Proteins that are exported outside the cell are made by ribosomes attached to a
series of membranes called the endoplasmic reticulum.
b) Endoplasmic reticulum- (ER) system of interconnected membranes, in between
the 2 layers are canals used to transport ER products, and materials from the
nucleus to the outer cell membrane.
There are 2 kinds of ER, Smooth and Rough
Rough Endoplasmic Reticulum
Rough Endoplasmic Reticulum
Rough ER- Endoplasmic reticulum that is covered in ribosomes and found in cells
that produce lots of proteins that are secreted to other areas of the body.
RER- This is the site for protein synthesis.
Smooth Endoplasmic Reticulum
Smooth ER- it is ER that does not have any ribosomes, so it does not produce
any proteins.
It is thought to serve as an intracellular highway or storage are for proteins
that are to be transported later.
Smooth ER is often connected at the end of the Rough Endoplasmic Reticulum
It is also linked to lipid synthesis and detoxification of drugs. Ex: Liver
• Golgi apparatus- system of flattened membranous sacs that
transport proteins and lipids and modify vesicles as they
go. They get address labels and are directed to various
parts of the cell
• Lysosomes- vesicles that bud from Golgi Apparatus and
have digestive enzymes. These enzymes break down
proteins, carbs and nucleic acids.
– Within the cell lysosomes digest old and worn out
organelles called autophagy
– The digestion of old cells is called autolysis, these
process help to keep health and organism functioning
• http://www.youtube.com/watch?v=suN-sV0cT6c
• In step 1 , proteins are assembled by ribosomes on the
rough ER.
• 2 , vesicles transport proteins to the Golgi apparatus.
• 3 , the Golgi modifies proteins and pack- ages them in
new vesicles.
• 4 , vesicles release proteins that have destinations
outside the cell.
• 5 , vesicles containing enzymes remain inside the cell
as lysosomes, peroxisomes, endo- somes, or other
types of vesicles.
• Cytoskeleton- made of network of thin tubes it gives cell shape
and acts as tracks for items to move inside. Its functions based on
microtubules, microfilaments and intermediate filaments
• Microtubules- hollow tubes made of protein called tubulin, each
radiates from central point called centrosome
• Microfilaments- long threads of protein actin wrapped around
each other and help with movement of white blood cells and
muscle contractions
• Intermediate filaments- rods that anchor nucleus and some
organelles in place ( hair follicle)
• Cilia and Flagella- hair like structures that extend from cell, cilia
are numerous, flagella are longer and fewer. They aid in
movement like oars on a boat or swimming motions
• Centrioles-occur in animal cells and consist of 2 short cylinders of
microtubules and located in cytoplasm near nucleus and organize
the microtubules of cytoskeleton during cell division
PLANT CELLS
• Cell wall- rigid layer found in plants lies outside plasma
membrane
• Central vacuole- large fluid filled organelle stores water,
enzymes, waste, and can make up to 90% of cell volume
• Plastids- organelles surrounded by double membrane like
mitochondria and have DNA. Chloroplasts, chromoplasts,
leucoplasts
• Chloroplasts- use light energy to make carbohydrates from CO2
and water
• Thylakids-system of flattened sacs
• Chlorophyll- contained in thylakids, green pigment absorbs light
• Chromoplasts-plastids that contain pigment and may or may not
contribute to photosynthesis. (orange, red, yellow, white)
• Proplastid- precursor to amyloplasts, chloroplasts, chromoplasts
• Prokaryotes vs. Eukaryotes-Prokaryotes lack nucleus
and membrane bound organelles, they have a nucleoid
and lack inner membrane system
• Plant cells vs. Animal cells– Production of cell wall
– Large central vacuole
– Plastids