General Features of cells

Cell Theory

  1. All living organisms are composed of cells.
  2. Cells are smallest units of life
  3. Cell division

Eukaryotes : more complex cells. - DNA within a membrane bound nucleus. Internal membranes form organelles.

Compartmentalized functions

Organelles: membrane-bound.
each structure has a specific function

Variety: shape, size, and organization of cells vary. differences between species and specialized cell types

Animal cell:
-no cell wall
-no chloroplast
-have many small vacuoles
-nucleus is present at the center of cell
-contains lysosomes
-contains centrioles near the nucleus
-irregular in shape

Both animal and plant cells contain:
-nucleus
-mitochondria
-cell membrane
-cytoplasm
-golgi apparatus
-endoplasmic reticulum and ribosomes

Plant cells:
-cell wall
-chloroplasts
-large central vacuole
-have definite shape
-nucleus pushed to one side of the cell.

Genomes and Proteomes: DNA in each cell is identical but differs in it's proteomes.

structure determines function

protein profile varies on

  1. which proteins are expressed
  2. levels of expression.
  3. which subtypes of proteins are expressed.
    1. post- translational modifications.

The cytosol: region of a cell that is outside the organelles but inside the plasma membrane.
cytoplasm includes: cytosol, endomembrane system, semiautonomous organelles

Molecular synthesis:

Anabolism: synthesis of cellular molecules and macromolecules

Catabolism: breakdown of a molecule into simple components

Cytosol: a central coordinating region for metabolic activities in eukaryotes

Cytoskeleton

Intermediate filaments: intermediate in size , form twisted and rope-like structures, are more permanent in nature

Actin filaments: also called microfilaments, long, thin fibres and dynamic.

Microtubules: long, hollow, cylindrical, dynamic instability

Motor proteins

Use ATP as a source of energy

Movements

Motor protein carries cargo along the filament

Motor protein remains in place, filament moves

Motor protein and filament restrained- action of the motor protein exerts force that bends the filament.

Prokaryotes : simple cell structure - no nucleus

Features of a typical bacterial cell:

Outside plasma membrane:
cell wall- for support and protection
glycocalyx- traps water, gives protection and helps in the immunity
appendages - for movements- flagella- pilli- for attachments

Inside plasma membrane:
cytoplasm - contained within plasma membrane.
Nucleoid region- where DNA is located
Ribosomes- synthesize proteins.

Archaea

-small cells, - less common - found in extreme environments

Bacteria

-small cells, - very abundant in the environment and our body, -majority not harmful to humans, - some species cause diseases

Organelles

Nucleus: contains chromosomes- composed of DNA + proteins = Chromatin
Nuclear matrix- nuclear lamina + internal nuclear matrix = filamentous network
Ribosome assembly in the nucleolus


Nuclear envelope: double-membrane
outer membrane is continous with the ER envelope
Nucleus pores provide entryways
Materials within the nucleus are NOT part of the endomembrane system.

ER- cisternae- flattened, fluid filled tubules. Enclosed around a single compartment- ER lumen.

Smooth: lacks ribosomes, functions : detoxification, carbohydrate metabolism, calcium balance, synthesis and modification of lipids.

Rough: studded with ribosomes.
functions: protein synthesis and sorting, insertion of protein into ER membrane
Glycosylation

Golgi Body: stack of flattened, membrane-bound sacs.
Vesicles transport material between the sacs
Functions: secretion, processing, and protein sorting

Lysosomes: contain acid hydrolases that perform hydrolysis under acidic conditions.

Lipids

Proteins

Carbohydrates

Nucleic acids

Digestion of substances from outside by endocytosis
Recycling of worn-out organelles- autophagy

Many different types of hydrolases to break down:

Vacuoles:

Central: for storage and support to maintain pressure (turgor pressure in plants)

Contractile: for movement, in protists to expel water

Phagocytic: in protists and white blood cells for degradation

Peroxisomes: catalyze by removing hydrogen or adding oxygen- hydrogen peroxide a byproduct. Catalase breaks down the dangerous product into water and oxygen
peroxisomes = glyoxysomes in plant seeds.

Plasma membrane

Cell signalling

membrane transport

Cell adhesion

Semiautonomous organelles

Mitochondria: grow and divide to reproduce themselves, are semiautonomous because they depend on cell for synthesis for internal components

Function: to make ATP.
Outer and inner membrane - intermembrane space and matrix
Involved in synthesis and modification of different molecules
contain their own DNA and divide via binary fission

Chloroplasts : grow and divide to reproduce themselves, are semiautonomous because they depend on cell for synthesis for internal components

Function: photosynthesis
Outer and inner membrane- intermembrane space and thylakoid membrane
contain own DNA and divide via binary fission

Protein sorting to organelles

cotranslational sorting

For ER, Golgi, lysosomes, vacuoles, plasma membrane and secreted proteins

Post translational sorting

Begins in cytosol during translation

Involves sorting signals and vesicle transport

Most proteins for nucleus, mitochondria, chloroplasts and peoxisomes

Synthesized in cytosol and translated later