Bio 178 Lecture 8Cell Structure

Copyright: J. Elson-Riggins

Reading

• Chapter 5

Quiz Material

• Questions on P 104

• Chapter 5 Quiz on Text Website (www.mhhe.com/raven7)

Outline

• Eukaryotic Cells (Cntd.)

The Golgi Apparatus

StructureFlattened membranous sacs (cisternae).

Functions

• Collection, packaging, sorting, and shipping of ER products.

• Modification (in particular glycosylation) of proteins and lipids.

Orientation• Cis - Receiving end.

• Trans - Discharging end.

Golgi Apparatus

Protein Transport from ER to Golgi

Golgi Apparatus

http://wilfred.berkeley.edu/TEM-Gallery1/pages/Golgi.htm

Golgi Apparatus

http://www.siena.edu/biology/faculty/cellbiology/golgi.jpg

Lysosomes

Structure• Membrane bound vesicles that contain hydrolytic emzymes. Enzymes only function at acidic pH.

• pH 5 in secondary lysosomes maintained by proton pumps in the membrane.

• Primary lysosomes not acidic.

Functions

• Organelle breakdown & recycling.

• Phagocytosis.

Lysosome Fusing

http://www.jdaross.mcmail.com/lysosome.htm

McGraw-Hill Video : Lysosomes

Organelles that Contain DNA

• Mitochondria

• Chloroplasts

Mitochondrion

Chloroplast

Organelles that Contain DNA Mitochondria & chloroplasts

Formation of DNA Containing Organelles:The Endosymbiont Theory

• The Theory

Mitochondria & chloroplasts were derived from prokaryotes that were engulfed by the ancestral eukaryote.

• Evidence1. 2 membranes - inner folded

2. Size

3. Own circular DNA

4. Ribosomes

5. Division

Endosymbiosis

Mitochondrion

The MitochondrionSize~ 0.5-1 µm diam

Membranes• Outer - smooth

• Inner - highly folded into cristae with embedded proteins that function in oxidative metabolism.

Compartments• Outer - intermembrane space

• Inner - matrix

FunctionsCellular respiration.

The Mitochondrion (Cntd)DNA• Own Circular DNA1. Contains several genes encoding proteins for oxidative

metabolism.

2. Synthesis of these proteins uses RNA and ribosomal components encoded by its own DNA.

• Use of Nuclear DNA

1. Nuclear DNA encodes the rest of the proteins required for oxidative metabolism.

2. Also encodes proteins required for mitochondrial division.

The Mitochondrion

Extracted DNA

DNA (arrow) & ribosomes (circle)

http://cellbio.utmb.edu/cellbio/mitoch2.htm

Chloroplast

The ChloroplastSize~ 2 µm X 5 µm

Membranes• Outer & inner membranes - smooth

• Thylakoid membrane - Forms flattened disks (thylakoids), which are stacked to form grana. Photosynthetic pigments in membrane.Compartments• Stroma - bathes thylakoids

• Thylakoid space - inside thylakoidsFunctionsPhotosynthesis

The Chloroplast (Cntd)DNA• Own Circular DNA

Some chloroplast proteins encoded here.

• Use of Nuclear DNA

Remaining chloroplast proteins encoded here.

The Cytoskeleton

The CytoskeletonComposition

• Network of protein fibers.

• Composed of actin (microfilaments), microtubules, & intermediate filaments.

Functions• Structure

• Transport

• Cell division

• Locomotion

• Anchoring of organelles

Distribution of The Cytoskeleton

Intermediate Filaments

Microtubules Actin Filaments

http://www.tmd.ac.jp/artsci/biol/textbook/cellmove.htm

The Cytoskeleton

Actin Microtubules Intermediate Filaments

http://cellix.imolbio.oeaw.ac.at/Videotour/video_tour_1.html

Dynamic Nature of the Cytoskeleton

Actin filaments and microtubules are constantly assembling (polymerization) and disassembling (depolymerization).

• Plus end - Fast growing end

• Minus end - Slow growing end

Actin (Microfilaments)

http://cellix.imolbio.oeaw.ac.at/Videotour/video_tour_1.html

Fibroblast labeled with fluorescent phalloidin.

Actin (Microfilaments)

http://www.microscopyu.com/articles/fluorescence/filtercubes/yfp/yfphyq/actin/yfpactinindex.html

Actin Filaments

Size

~ 7 nm diam

Composition

2 intertwined chains of the globular protein actin.

Functions of Actin filaments

• Muscle contraction

• Cellular extensions

• Cleavage furrow

• Anchoring

• Movement

Microtubules

Functions

• Movement of organelles

• Chromosome movement