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