Chapter 4:General Features of Cells
Cell theory
All living organisms are composed of one or more cells
smallest units of life
New cells come only from pre-existing cells by cell division
categories of life
Prokaryotes
Eukaryotes
Simple cell structure
No nucleus
complex cells
DNA enclosed within membrane-bound nucleus
Internal membranes form organelles
categories
Archaea
Bacteria
Less common
Often found in extreme environments
Also small cells, 1 μm – 10 μm in diameter
abundant in environment
Vast majority are not harmful to humans
but some are
Small cells, 1 μm – 10 μm in diameter
Typical bacterial cell
Inside the plasma membrane
Outside the plasma membrane
Nucleoid region
Ribosomes
Cytoplasm
Glycocalyx
Appendages
Cell wall
flagella (movement)
pilli (attachment)
Variety
Differences between
Shape, size, and organization of cells vary considerably
specialized cell types
species
Animal cell
Plant cell
Chromatin
Plasma membrane
Ribosome
Cytosol
Lysosome
Golgi apparatus
Nucleolus
Peroxisome
Nuclear envelope
Cytoskeleton
Nucleus
ER
Mitochondrion
Centrosome
same as animal cell except
Cell wall exists
Central vacuole exists
Centrosome absent
Region of a eukaryotic cell that is outside the cell organelles but inside the plasma membrane
Molecular synthesis and breakdown
Anabolism
Catabolism
Breakdown
Synthesis
Cytosol is central coordinating region for metabolic activities of eukaryotic cells
three types of protein filaments
Intermediate filaments
Actin filaments
Microtubules
Motor Proteins
such as myosins and kinesins
move along cytoskeletal filaments via a force-dependent mechanism driven by the hydrolysis of ATP
Three domains
hinge
tail
head
Walking analogy
The ground is the cytoskeletal filament, your leg is the head of the motor protein, and your hip is the hinge
Chromosomes
Endomembrane System
Network of membranes enclosing the nucleus, endoplasmic reticulum, Golgi apparatus, lysosomes, and vacuoles
includes plasma membrane
Double-membrane structure enclosing nucleus
Outer membrane of the nuclear envelope is continuous with the ER membrane
Nuclear pores provide passageways
Nuclear matrix
Ribosome assembly
Composed of DNA and proteins
Network of membranes that form flattened, fluid-filled tubules or cisternae
encloses ER lumen
rough ER
smooth ER
Studded with ribosomes
protein synthesis and sorting
Lacks ribosomes
Detoxification, carbohydrate metabolism, calcium balance, synthesis, and modification of lipids
processing
protein sorting
Secretion
Contain acid hydrolases that perform hydrolysis
break down proteins, carbohydrates, nucleic acids, and lipids
Autophagy
Recycling of worn-out organelles through endocytosis
Vacuoles
Contractile vacuoles in protists for expelling excess water
Central vacuoles in plants for storage and support
Phagocytic vacuoles in protists and white blood cells for degradation
Catalyze certain reactions that break down molecules by removing hydrogen or adding oxygen
H2O2 is a byproduct
Catalase breaks down dangerous H2O2 into water and oxygen
Boundary between the cell and the extracellular environment
Functions
Membrane transport
Cell signaling
Cell adhesion
Semiautonomous Organelles
chloroplasts exist
Grow and divide to reproduce themselves
They are not completely autonomous because they depend on the cell for synthesis of internal components
Primary role is to make ATP
has Outer and inner membrane and intermembrane space
Contain its own DNA, divide by binary fission
Photosynthesis
(chapter 8)
Found in nearly all species of plants and algae
Outer and inner membrane
like mitochondria
Contain their own DNA, divide by binary fission
also like mitochondria
Protein Sorting to Organelles
Cotranslational sorting
Post-translational sorting
For ER, Golgi, lysosomes, vacuoles, plasma membrane, and secreted proteins
Begins in cytosol during translation
Involves sorting signals and vesicle transport
Most proteins for nucleus, mitochondria, chloroplasts, and peroxisomes
Synthesized in cytosol and sorted later