Cellular Classification & Organelles: A Look at the Endomembrane System

Biology 111

Holyoke Walsh

Cells

• http://www.youtube.com/watch?v=IcevP5tkWH0&feature=related

COMPARING CELLS

• The size & shape of a cell relates to its function.

Cells

• All cells are classified as either 1. Prokaryote2. Eukaryote

Prokaryote Cells• no membrane bound nucleus, chromosomes

grouped together in an area called the "nucleoid"• no membrane bound organelles• smaller than eukaryotes

• have cell wall and cell membrane, some have a capsule on the outside

• ribosomes make protein• consist of bacteria and

archaebacteria• Appendages

include: fimbriae/pili, flagella

*pili are usually longer and fewer than fimbriae, both function for attachment and recognition of host cells (pili has a function for sexual reproduction)

Figure 4.4a

E. coli

Eukaryotes• has a membrane bound nucleus• has membrane bound organelles in cytoplasm• Organelles perform specific functions• much larger than prokaryotes

Organisms within the animal, plant, fungi and protista kingdoms are all eukaryotes

We will be spending a lot of time on organelles and their functions.

Figure 4.6b

Figure 4.7b

Prokaryote vs Eukaryote CellsEndosymbiosis theory: 

All organelles seem to share many properties with bacteria. Lynn Margulis proposed endosymbiont hypothesis: that organelles derived from ancient colonization of large bacteria (became the eukaryotic cell) by smaller bacteria (became the mitochondria, chloroplast, etc.) Symbiosis = "living together". *Mitochondria & Chloroplasts have their own DNA

Animation at Microbiological Concepts

Commonalities…of all cells!!

• Plasma Membrane• Cytoplasm• Chromosomes (DNA)• Ribosomes

Key Differences?

• The location of their DNA; membrane bound organelles

• Prokaryote = nucleoid region• Eukaryote = nucleus

Prokaryote vs. Eukaryote

Prokaryote or Eukaryote??

Prokaryote or Eukaryote??

Prokaryote or Eukaryote??

Eukaryotes• In addition to the plasma membrane at its outer

surface, a eukaryotic cell has extensive & elaborately arranged internal membranes, which divide the cell into compartments.

• These provide different local environments that facilitate specific metabolic functions, so incompatible processes can go on simultaneously in a single cell

• The plasma and organelle membranes participate directly in the cell’s metabolism b/c many enzymes are built right into the membranes themselves.

Cell Membranes..in general

• Phospholipid bilayer• Embedded proteins• Each type of membrane has a unique

composition of lipids and proteins suited to that membrane’s specific function

Ex: enzymes embedded in the mitochondrial membrane function in cellular respiration…which creates the ATP energy our cells need to function!

Cell Membrane

Pg 64

Eukaryotes…genetic info…

• Two cellular components involved with the genetic control of the cell are the NUCLEUS & the RIBOSOMES

NUCLEUS

The Nucleus

The Nucleus• Nuclear envelope contains nuclear pores for some things to enter and

exit (nucleoplasm within)• Chromatin is DNA and proteins, when the cell begins to divide, chromatin

condenses and forms chromosomes• DNA remains in the nucleus, it sends instructions to the cytoplasm via

messenger RNA• RNA directs the synthesis of proteins on ribosomes in the cytoplasm• Nucleolus assembles ribosomes within the nucleus, ribosomes contain

the "tools" to construct proteins

Chromosomes – made of DNA/Protein!

• DNA: Polymer of millions of nucleotidesNucleotide = Deoxyribose Sugar (pentose)+Phosphate + Nitrogen Base

29

One Strand of DNA• The backbone of

the molecule is alternating phosphates and deoxyribose sugar

• The teeth are nitrogenous bases.

phosphate

deoxyribose

bases

DNA Double Helix

T

G

C

G

G

A

C

C

A T Bases: Cytosine C Thymine T Adenine A Guanine G

http://www.youtube.com/watch?v=qy8dk5iS1f0

Ribosomes

• Made of some RNA (genetic info) and Protein• each is composed of two subunits, one large

and one small• Non-membranous organelles• Vary in size (smaller in prokaryotes)• Main function is to carry out protein

synthesis.

Ribosomes cont…• Cells that have high rates of protein synthesis have

particularly high rates of ribosomes• Located in the cytoplasm/ER (structurally identical)• Free ribosomes – function within the cytosol (ie.

enzymes that catalyze reactions)• Attached ribosomes – generally destined for

insertion into organelles membranes or for export (cells that secrete enzymes)

• Why does the human pancreas have millions of ribosomes?