Cell Structure and Function

Robert Hooke-First person to see cells, he coined the term "cell" for the great many boxes he saw under the microscope

The Cell Theory

1. Every living organism is made of one or more cells
2. Cells are the functional unit of multicellular organisms
3. Cells arise from pre-existing cells

Cell Size

atoms --> DNA --> virus --> bacteria -->mitochondria--> Eukaryotic cells
Cells must remain small in size due to the ratio of surface area and volume
As the cell increases in size, its surface area becomes too small to support its internal structures. Oxygen and other important substances cannot diffuse fast enough. Cells that get too large, may divide.
All Cells Have Three Basic Features: Cell Membrane, Genetic Material, Cytoplasm
Plasma Membrane (aka Cell Membrane)
1. Isolates cytoplasm from external environment
2. regulates flow or material into and out of the cell
3. allows interaction with other cells
Genetic Material
1. provides cellular "blueprint" that controls the functions of the cell
2. In the form of DNA (Deoxyribonucleic acid)
3. DNA is universal for all cells, an all living things - evidence of common ancestry
4. Chromatin is the complex of proteins and DNA, it condenses into chromosomes before cell division
Cytoplasm (aka cyosol)
1. inside plasma membrane
2. contains water, salts, and other chemicals
3. organelles float within this jelly-like substance
Prokaryote vs Eukaryote Cells
Prokaryotes
  • no membrane bound nucleus, chromosomes grouped together in an area called the "nucleoid"
  • no membrane bound organelles
  • smaller than eukaryotes
  • have cell wall and cell membrane, some have a capsule on the outside
  • ribosomes make protein
  • consist of bacteria and archaebacteria
  • Appendages include: fimbriae, pili, flagella


Eukaryotes
  • has a membrane bound nucleus
  • has membrane bound organelles in cytoplasm
  • Organelles perform specific functions
  • much larger than prokaryotes
  • animals, plants, fungi, protists

The Parts of the Cell
The Nucleus
--nuclear envelope contains nuclear pores for some things to enter and exit (nucleoplasm within)
-- chromatin is DNA and proteins, when the cell begins to divide, chromatin condenses and forms chromosomes
--DNA remains in the nucleus, it sends instructions to the cytoplasm via messenger RNA
--RNA directs the synthesis of proteins on ribosomes in the cytoplasm
--Nucleolus assembles ribosomes within the nucleus, ribosomes contain the "tools" to construct proteins /
Endoplasmic Reticulum -- Transport System
(endoplasm means "within cytoplasm", reticulum means "little net"
--divides cell into compartments
--channels molecules through the cell's interior, like a little highway
Rough ER
--has ribosomes which give it its "rough" appearance
--functions in protein synthesis
--ER transports newly assembled proteins to the Golgi Apparatus
Smooth ER
--mostly contains enzymes that unction in lipid synthesis (such as hormones like estrogen and testosterone) /
Golgi Apparatus -- Delivery System
--flattened stacks of membranes
--functions in collection, packaging and distribution of molecules made in the cell and used elsewhere
-- front end (cis) faces the ER, and the back end (trans) faces the cell membrane
--the folded stacks are called cisternae
--unprocessed proteins enter the Golgi apparatus from ER
proteins are packaged and exported near membrane
Jobs of the Golgi Apparatus (aka Golgi Complex)
1. separates proteins according to their destinations
2. modifies proteins (adds sugar and makes glycoproteins)
3. packages materials into vesicles which are exported outside the cell - secretion /
Lysosomes - Intracellular Digestion Centers
--vesicles that are used to digest
--contain high levels of degrading enzymes
(to "lyse" means to dissolve)
--recycle old and worn out cell parts
--"suicide sac" - apoptosis
--digest other particles taken in by phagocytosis
--this "food" is stored in food vacuoles, the lysosomes fuse with the vacuoles and release digestive enzymes
--found in animal cells / TAY-SACHS disease – missing an enzyme of the lysosomes that breaks down a fatty substance. Over time this fat builds up in the brain and nervous tissue, smothering the cells. Results in degeneration and death.
Ribosomes - Sites of Protein Synthesis
--each is composed of two subunits, one large and one small
--mRNA is "read" by the ribosomes and amino acids are assembled into proteins
--ribosomes are manufactured by the nucleolus inside the nucleus
--polyribosomes – strings of ribosomes in the cytoplasm that work to make a protein /
Other Organelles
-- Peroxisomes – result in hydrogen peroxide, broken down by catalase
-- Vacuole -- mainly storage or specific functions (contractile vacuole)
-- Plant cells have a CENTRALVACUOLE - used for storage and help to maintain hydrostatic pressure /
ENERGY RELATED ORGANELLES
Mitochondria - The Cell's Chemical Furnaces
--contains its own DNA, support for Endosymbiosis Theory
--singular is "mitochondrion"
--2 membranes, one smooth outer membrane, and an inner membrane folded into layers called cristae
--Cristae has two compartments: the matrix and the intermembrane space
--mitochondria divide before cell division, they are not synthesized like other cell parts
--function to store energy for cell use. Energy is stored in the form of ATP - adenosine triphosphate /
Chloroplasts - Where Photosynthesis Takes Place
--only found in plant cells
--has its own DNA, like mitochondrion
--functions to convert light energy to carbohydrates
--carbohydrates then broken down in mitochondria to produce ATP
--consists of grana, closed compartments that are stacked
--thylakoids are the individual disk shaped compartments that make up the grana (stack of thylakoids)
--stroma is the fluid surrounded the thylakoids
*Chloroplasts are a type of plastid
Chromoplasts – red, yellow and orange pigment
Leucoplasts – colorless (potatoes) /
Cytoskeleton - Support System
Microfilaments (now called actin filaments) – occur in bundles, form tracks within the cell for the movement of organelles, used to form pseudopods (ameba)
Intermediate filaments - support membrane, cell to cell junctions
Microtubules - (little pipe) – regulated by the MTOC (microtubule organizing center), radiate from the centrosome - form the spindle during cell division
Centrioles–used during cell division to move and separate chromosomes, only found in animal cell /
Related to Movement
Pseudopod – extensions of the cell that allow for movement (ameba), depend on actin filaments
Cilia (hair)Flagella(whip)
--function in movement
-- 9+ 2 Arrangement of microtubules /