A Tour of the Cell Animals & Plants Chapter Five

Cell Study O Light microscope – up to 0.2  m; magnify well up to 1000x; not enough for many organelles

Cell Study O Electron microscope – up to 2nm (hundredfold improvement) – uses electron beam O Specimens must be “prepared” first O Two types

Cell Study O Scanning Electron Microscope (SEM) – used for surface study – appears 3-D O Cilia in the windpipe of a rabbit

Cell Study O Transmission Electron Microscope (TEM) – internal structure of cells O Uses magnets to bend electrons as they pass through O Cells from windpipe of a rabbit

Cellular Preparation O Cell fractionation – take cells apart & separate organelles for study O Ultracentrifuge – 130,000 rpm O Break cells apart (homogenization), then separate organelles (differential centrifugation)

Cellular Preparation

Cell Types O Prokaryotic – no nucleus O Bacteria & archaea O DNA in region called the nucleoid (has no membrane) O Have plasma membrane, chromosomes, ribosomes, cytosol

Cell Types

O Eukaryotic – have membrane-bound organelles suspended in cytosol, including a definite nucleus (cytosol + organelles = cytoplasm) O Eukaryotic =  m O Prokaryotic = 1-10  m

Eukaryotic Cells & Organelles

O Plasma Membrane O Selective barrier

Eukaryotic Cells & Organelles O Membrane of phospholipids, proteins, glycoproteins

Eukaryotic Cells & Organelles O Nucleus O Contains most genes O Surrounded by nuclear envelope – double lipid bilayer membrane with pores O Inner nuclear side lined with nuclear lamina (protein filaments for structure)

Eukaryotic Cells & Organelles O Inside, DNA is as fibrous chromatin O Will condense into chromosomes during division O Nucleolus O Inside nucleus O Ribosomal RNA (rRNA) made here & assembled to make ribosomes in cytoplasm

Eukaryotic Cells & Organelles

O Ribosomes O Two subunits made of ribosomal RNA & protein O Protein synthesis O Free or on ER (structurally identical) O Free make proteins that function in cytosol O Bound make proteins that are inserted into membranes, for packaging within other organelles, or exported

Eukaryotic Cells & Organelles

O ER (Endoplasmic reticulum) O Network of tubules & sacs – cisternae O Internal space – cisternal space O Two types

Eukaryotic Cells & Organelles

O Smooth ER O No outer ribosomes O Synthesis of lipids O Carbohydrate metabolism

Eukaryotic Cells & Organelles O Detoxify drugs & poisons, esp. in liver O Muscle cells – Smooth ER pumps calcium ions from cytosol to cisternal space – when muscle is stimulated, Ca rushes back over – triggers muscle contraction

Eukaryotic Cells & Organelles

O Rough ER O Produce secretory proteins O Protein is made, threads through pore into cisternal space, folds into proper shape O Most are glycoproteins

Eukaryotic Cells & Organelles O Secretory proteins leave ER wrapped in membranes of transport vesicles O Vesicles in transit throughout cell O Rough ER also makes membranes for endomembrane system (nuclear envelope, ER, Golgi, lysosomes, vacuoles, plasma membrane)

Eukaryotic Cells & Organelles O Golgi Apparatus O Manufacture, store, sort, ship products of ER O Flattened sacs (cisternae) O Two faces – cis (receive transport vesicles from ER) and trans (vesicles pinch off to other places)

Products move from cis to trans - modified & refined along the way

Eukaryotic Cells & Organelles

O Lysosomes O Hydrolytic enzymes  digestion O pH 5 O Enzymes made in rough ER, put through Golgi, then into lysosomes O Digest by fusing with food vacuole, bacteria, invaders

Eukaryotic Cells & Organelles O Autophagy – recycle own cell’s materials (like old organelles) O Organismal advantage – removal of webbed hands during embryonic development - tadpole has tail destroyed as it turns into a frog

Eukaryotic Cells & Organelles O If lysosomes can’t digest – lack of functioning enzyme – cell gets filled with indigestible materials O Tay-Sachs

Eukaryotic Cells & Organelles

O Vacuoles O Food, contractile, central O Central vacuole – in plants O Enclosed by tonoplast O Reserves of proteins, inorganic ions, metabolic wastes, pigments, animal warning system O Role in growth

Eukaryotic Cells & Organelles O Endomembrane System (organelles that are underlined)

Eukaryotic Cells & Organelles O Mitochondria – cellular respiration O Food  ATP O Semiautonomous organelle O Two layers – each phospholipid bilayer O Outer membrane - smooth O Inner is convoluted – cristae

Eukaryotic Cells & Organelles O Separates into two compartments O Intermembrane space – between outer and inner membranes O Mitochondrial matrix – inside O Contains DNA, enzymes, ribosomes

Eukaryotic Cells & Organelles O Chloroplasts O Site of photosynthesis O Two membranes O Inside are thylakoids (sacs) – each is called a granum O Fluid outside thylakoid – stroma (contain DNA, ribosomes, enzymes)

Eukaryotic Cells & Organelles O Peroxisomes O Contain enzymes that transfer hydrogen to oxygen, making H 2 O 2 (hydrogen peroxide) O Organelle helps detoxification, fatty acid hydrolysis O Then converts H 2 O 2 to H 2 O

Cytoskeleton O Network of fibers O Support & shape O Anchorage for organelles & enzymes

Cytoskeleton O Cell motility O Interaction with motor molecules (proteins) O Movement of cilia & flagella – cytoskeleton components can slide past each other O Contraction of muscle cells O Organelles can move within cell

Cytoskeleton O Three fibers

Cell Walls O Protects, shape, prevents excessive water uptake O Cellulose embedded in protein/polysaccharide matrix O As young plant, makes primary cell wall

Cell Walls O Between walls of adjacent cells –middle lamella (rich in pectins – thick) O Cell stops growing – makes thicker secondary cell wall

Extracellular Matrix (ECM) O Surface of animal cells O Glycoproteins (mostly collagen) embedded in proteoglycan network

Extracellular Matrix (ECM) O Cells attached to ECM by fibronectins (glycoprotein)  Bind to integrins (receptor molecules on plasma membrane)  Attach ECM to plasma membrane to coordinate any changes O ECM can coordinate cell’s behavior

Intercellular Junctions O Plasmodesmata – perforations in plant cell walls O Allows cytosol, water, proteins, RNA, small solutes to pass between O Plasma membrane lines channel

Intercellular Junctions O Animal cells: 1. Tight junctions – membranes of neighboring cells are fused – prevent EC fluid leakage 2. Desmosomes (anchoring junctions) – fastens cells into strong sheets like rivets

Intercellular Junctions 3.Gap junctions (communicating junctions) – provides cytoplasmic channel between adjacent cells O Allows small ions & molecules to pass O Flow of ions coordinates cell contractions