Cell Theory
-all organisms are composed of one or more cells
-cells are the smallest living units of all living organism
-cells arise only by division of a previously existing cell
Genetic Material
-single cellular molecule in prokaryotes
-double helix located in nucleus in eukaryotes
Cell Characteristics
Cytoplasm fills the cell
Plasma membrane encloses the cell
Rate of diffusion is affected by:
-surface area available
-temperature
-concentration gradient
-distance
Why are most cells relatively small?
Cell size is limited due to reliance on diffusion of substances in and out of cells
Important people with cells
Robert Hooke-discovered cells in 1665
Schlieden and Schwann- conducted early studies of cells and proposed the cell theory
Resolution
minimum distance two points can be apart and still be distinguished as two separate points (objects must be 100 um apart for naked eye to resolve them as two objects)
2 types of microscopes?
1. light microscopes- use magnifying lenses with visible light, resolve structures that are 200 um apart, limit to resolution using light
2. Electron microscopes- use beam of electrons, resolve structures that are 0.2 nm apart
Electron microscope types
-transmission electron microscopes: transmit electrons onto specimen surface (good 2D image)
-scanning electron microscopes beam electrons and produce good 3D
Structural similarities
1. Nucleoid or nucleus where DNA is located
2. Cytoplasm- semifluid matrix of organelles and cytosol
3. Ribosomes- synthesize proteins
4. Plasma Membrane- phospholipid bilayer
Prokaryotic Cells
-Simplest organisms
-lack a membrane-bound nucleus (DNA is present in nucleoid)
-cell wall outside of plasma membrane
-do contain ribosomes (not membrane-bound organelles)
-two domains of prokaryotes: archaea and bacteria
Bacterial cell walls
-composed of peptidoglycan
-protect cell, maintain its shape and prevent excessive uptake or loss of water
-susceptibility of bacteria to antibiotics often depends on the structure of cell walls
-archaea lack peptidoglycan
Eukaryotic Cell
-compartmentalization of an endomembrane system, and presence of membrane-bound organelles
-plant and animal cell
-cytoskeleton for support and cellular structure maintenance
Difference between plant and animal cells
Plant cells have chloroplast, vacuoles and a cell wall outside the cell membrane
Nucleus function
inheritance and RNA production
Mitochondrion
Energy production (powerhouse of cell)
Endoplasmic reticulum
protein and lipid production
Golgi
Glycosylation, secretion
Lysosomes
Degradation
Peroxisomes
Degradation, detoxification
Nucleus
Most eukaryotic cells possess a single nucleus
Nucleolus - region where ribosomal RNA synthesis takes place
Nuclear envelope
2 phospholipid bilayers
Nuclear pores - control passage in and out
In eukaryotes, the DNA is divided into multiple linear chromoso
Chromosomes
DNA is organized in discrete segments called chromosomes.
Humans have 23 pairs of chromosomes:
- 22 autosome pairs which are the same in both sexes
- 1 pair of sex chromosomes, the X and the Y
Each chromosome includes hundreds of different genes.
DNA of e
Endomembrane System
- a series of membranes throughout the cytoplasm
- divides cell into compartments where different cellular functions occur
-one of the fundamental distinctions between a prokaryotic and an eukaryotic cell
Smooth and Rough ER
Interconnected membranous tubules and sacs
Rough ER (RER) contains ribosomes, site of protein synthesis
Smooth ER (SER) does not contain ribosomes and is important in lipid synthesis
Ratio of RER to SER is dependent on cell's function
Ribosomes
Cell's protein synthesis machinery
Found in all cell types in all 3 domains
Ribosomal RNA (rRNA)-protein complex
Protein synthesis also requires messenger RNA (mRNA) and transfer RNA (tRNA)
Ribosomes may be free in cytoplasm or associated with internal me
Golgi Apparatus
collection of Golgi bodies (flattened sacs of interconnected membranes)
Has cis (receiving side), medial and trans (shipping side)compartments
Function:
collects, packages and distributes molecules (using vesicles) synthesized at one location in the cell
Vesicular Endomembrane System
Vesicles
Lysosomes - membrane-bound digestive vesicles
Microbodies - enzyme-bearing, membrane-enclosed vesicles.
Peroxisomes - contain enzymes that catalyze the removal of electrons and associated hydrogen atoms
lysosomes
Membrane-bounded digestive vesicles
Arise from Golgi apparatus
Enzymes catalyze breakdown of macromolecules
Destroy cells or foreign matter that the cell has engulfed by phagocytosis
-degrade cellular debris and recycle cell contents.
Phagocytosis
Insoluble
Pinocytosis
Soluble
Microbodies
Variety of enzyme-bearing, membrane-enclosed vesicles
Peroxisomes
Contain enzymes involved in the oxidation of fatty acids
Hydrogen peroxide produced as by-product - rendered harmless by catalase
Secretory Pathway
Milk protein genes transcribed into mRNA
2) mRNA exits thru nuclear pores
3) mRNA forms complex and moves to surface of rough ER where protein is made
4) enzymes in smooth ER manufacture lipids
5) proteins and lipids are packaged into vesicles in both rou
Organelles with own DNA
Mitochondria
bounded by exterior and interior membranes
interior partitioned by cristae
Power house of the cell (generates ATP for cellular function)
Chloroplasts
have enclosed internal compartments of stacked grana, containing thylakoids
found in photosy
Mitochondria
POWER HOUSE OF THE CELL
OXIDATIVE PHOSPHORYLATION - GENERATION OF ATP
SEVERAL THOUSAND MITOCHONDRIA PER CELL
MATERNALLY INHERITED
CIRCULAR DNA
Chloroplast
- organelles present in cells of plants and some other eukaryotes
- contain chlorophyll for photosynthesis
- surrounded by 2 membranes
- thylakoids are membranous sacs within the inner membrane
- grana are stacks of thylakoids
vacuoles
Membrane-bounded structures in plants
Various functions depending on the cell type
There are different types of vacuoles:
Central vacuole in plant cells (gets bigger as it accumulates more nutrients inside)
Contractile vacuole of some fungi and protists
S
Cytoskeleton
Fibers, filaments and their associated proteins
Dynamic - constantly assembling and disassembling
Not membrane bound
Cytoskeleton functions
Maintain cell shape
Connect cells to each other
Transport organelles and small molecules
Provide cell motility (some cell types)
Move chromosomes
Compose cilia
Cytoskeleton Makeup
Actin filaments - 7nm in diameter, globular protein actin, contraction, crawling or pinching
Microtubules - 25nm in diameter, ? and ? tubulin, centrioles, organization of cytoplasm and movement of cargo in the cell, largest of these filaments
Intermediate
Centrosomes
Region surrounding centrioles (where can have nucleation occur for microtubules) in almost all animal cells
Microtubule-organizing center
Can nucleate the assembly of microtubules
Animal cells and most protists have centrioles - pair of organelles
Plants
Centrioles
Made of microtubule triplets (3 strands from this) and a cytoskeleton filament
Cell Movement
Essentially all cell motion is tied to the movement of actin filaments, microtubules, or both
Some cells crawl using actin microfilaments
Flagella (whip like structure to help bacteria move) and cilia have 9 + 2 arrangement of microtubules
Not like prokar
Motor proteins
KINESIN - moves vesicles towards the edge or periphery of the cell
DYNEIN - moves cargo or vesicles toward the center of the cell
Plant and animal cell structure
Plant cells have a cell wall based of cellulose which gives it rigidity and strucutre
Animal cells have a cytoskeleton and this is linked to the ECM proteins by means of other proteins called Integrins.
Eukaryotic cell walls
Plants, fungi, and many protists
Different from prokaryote
Plants and protists - cellulose
Fungi - chitin
Plants - primary and secondary cell walls
Extracellular matrix (ECM)
Animal cells lack cell walls
Secrete an elaborate mixture of glycoproteins into the space around them
Collagen may be abundant
Form a protective layer over the cell surface
Integrins link ECM to cell's cytoskeleton
Influence cell behavior
ECM proteins
proteins made inside cell and secreted outside, integrin connects two sections across the bilayer
Cell-to-cell interactions
Surface proteins give cells identity
Cells make contact, "read" each other, and react
Glycolipids - most tissue-specific cell surface markers
MHC proteins - recognition of "self" and "nonself" cells by the immune system (cells in body have to recognize "t
Cell connection types
3 categories based on function
Tight junction
Connect the plasma membranes of adjacent cells in a sheet - no leakage
Anchoring junction
Mechanically attaches cytoskeletons of neighboring cells (desmosomes)
Communicating junction
Chemical or electrical sig
Plasmodesmata
Plant cells
Plasmodesmata
Specialized openings in their cell walls
Cytoplasm of adjoining cells are connected
Function similar to gap junctions in animal cells