Lecture 4 Cells Reading: Chapter 6

All life is based on a unit of organization we call the cell There are two basic cell architectures: Prokaryotic Eukaryotic

Sizes of things

Prokaryotic Cells

Escherichia coli Bacillus polymyxis

Eukaryotic Cells Eukaryotic cells are much more complex than prokaryotic cells Eukaryotic cells are usually much larger than prokaryotic cells Most Prokaryotes are single celled Many Eukaryotes are single celled Many Eukaryotes are multi-celled

Animal Cell

Plant Cell

Some major differences between animal and plant cells Plant cells have a cell wall Plant cells have chloroplasts (plastids) Plant cells have a central vacuole Plant cells have plasmodesmata Animal cells have lysosomes Animal cells have centrioles Many animal cells are ciliated

Similarities between plant and animal cells Nucleus Mitochondria Endoplasmic reticulum Golgi Vesicles Peroxisomes Cytoskeleton Centrosome Flagella (some cells)

Things all cells (both prokaryotic and eukaryotic) have in common: Plasma membrane DNA Central role for proteins Same genetic code Mechanism of protein synthesis Ribosomes, mRNA, tRNA Many metabolic pathways

Nucleus and cytoplasm (Eukaryotic cells) Nucleus contains DNA Bounded by two membranes Inner and outer nuclear membrane Nuclear pores Nucleus contains no ribosomes Site of most DNA and RNA synthesis The cytoplasm includes everything between the plasma membrane and the nuclear membrane - ribosomes

nucleus

Ribosomes Ribosomes are found bound to the ER (rough ER) and free in the cytosol Ribosomes are the site of all protein synthesis Ribosomes have no membrane as part of their structure (made of RNA and protein)

Endomembrane system Endoplasmic reticulum Golgi Transport vesicles Smooth Rough Golgi Transport vesicles Central vacuole (plants)

Endoplasmic reticulum Site of much protein synthesis Site of most membrane synthesis

Golgi Stack of membrane sacks Processing and transport center Transport is by vesicles ER lysosomes Plasma membrane

Lysosomes Site of protein and polysaccharide degradation (animal cells) Provides major protection from foreign microorganisms (bacteria and viruses) pH inside is about 5 (low). This activates digestive enzymes

Vesicle transport system ER Golgi Plasma memb. Lysozomes Vacuoles Vesicles Exocytosis

Vacuoles Central vacuole (plants) Phagosome (phagocytic cells) Amoeba Macrophages Contractile vacuole Protists

Energy Mitochondria (all eukaryotic cells) “powerhouse of the cell” Site of respiration (O2 + CH  CO2 +H2O) Major source of ATP Chloroplasts (all eukaryotic plant cells) Site of photosynthesis H20 + CO2 + light  glucose + O2 Ultimate source of chemical energy for most of life

Mitochondria Two membranes Have DNA and ribosomes Inner mitochondrial membrane Site of respiration Outer mitochondrial membrane Have DNA and ribosomes

Chloroplasts Three membranes Have DNA and ribosomes Outer Inner Thylakoid (site of photosynthesis) Have DNA and ribosomes

Other membrane bound organelles Plastids (related to chloroplasts) Starch storage (roots) Pigment (flowers) Have DNA and ribosomes Peroxisomes (both plants and animals) Single membrane H transfer reactions (to oxygen) Detoxification Protection from oxidative damage

Cytoskeleton All protein

Microfilaments (thin filaments) Intermediate filaments Microtubules α and β tubulin Microfilaments (thin filaments) actin Intermediate filaments (more than a dozen types with a similar overall structure) Thick filaments (muscle) myosin

Microtubules and transport in cell Molecular motors Molecular “walking machines” Can work on both micro- filaments and microtubules

Microtubules and cell movement Flagella Cilia

Flagellum and Cilium Structure Dynein = molecular motor

How does it work?

Microtubules and chromosome movement Centrioles (animal cells) Organize flagella Organize spindle Cell centers (plant cells)

Figure 12.5

Actin and cell movements Membrane and cytoplasmic movements involve microfilaments

Structures outside the plasma membrane Cell walls (plants, fungi, many protists) Extracellular matrix (animals) Polysaccharides (mucus, slime) Junctions

Plant cell walls

Extra cellular matrix

Junctions