Cellular Classification & Organelles:

A Look at the Endomembrane System

Biology 111

Holyoke Walsh

Cells

• All cells are classified as either

1.Prokaryote

2.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

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

Endosymbiosis 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".

IOW..Mito/Chloro were ancient prokaryotes and they became part of another

prokaryote in a mutualistic/symbiotic relationship  

*Mitochondria & Chloroplasts have their own DNAAnimation 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

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 nucleotides

Nucleotide = Deoxyribose Sugar (pentose)

+Phosphate + Nitrogen Base

24

One Strand of DNAOne 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?

Protein Synthesis Summary

Protein Synthesis 1. The DNA double helix unwinds to expose a sequence of

nitrogenous bases. (A,T,C,G)

2. A copy of one of the strands is made in a process known as transcription. The copy is made of messenger ribonucleic acid (mRNA) which, following transcription, travels out of the nucleus into the main body of the cell, where protein synthesis occurs.

3. The mRNA couples with the protein synthesis apparatus (the ribosome). Another type of RNA, known as transfer RNA (tRNA), brings free amino acids to the ribosome.

4. The anticodon present on the tRNA recognises the codon present on the mRNA, and the ribosome adds the amino acid to the growing chain of linked amino acids (polypeptides), cleaving it away from the tRNA. This process is known as translation.5. As the polypeptide chain grows, it folds to form a protein.

http://www.youtube.com/watch?v=983lhh20rGY

ENERGY RELATED ORGANELLES

Mitochondria - The Cell's Chemical Furnaces •contains its own DNA, support for Endosymbiosis Theory•singular is "mitochondrion“•2 membranes, one smooth outer membrane, and an inner membrane folded into layers called cristae•Cristae has two compartments: the matrix and the inter membrane space

• function to store energy for cell use. Energy is stored in the form of ATP - adenosine triphosphate

• (Made by cellular respiration… which we will learn later!)

Figure 4.17

Chloroplasts - Where Photosynthesis Takes Place • only found in plant cells• has its own DNA, like

mitochondrion

• functions to convert light energy to carbohydrates

• carbohydrates then broken down in mitochondria to produce ATP

• consists of grana, closed compartments that are stacked

• thylakoids are the individual disk shaped compartments that make up the grana (stack of thylakoids)

• stroma is the fluid surrounded the thylakoids

*Chloroplasts are a type of plastid

Chromoplasts – red, yellow and orange pigmentLeucoplasts – colorless (potatoes)

Endomembrane System

• Many of the different membranes of the eukaryotic cell are part of this system which carry out a variety of tasks in the cell. i.e. synthesis of proteins, metabolism and movement of lipids, & detoxification of drugs and poisons

• The membranes of this system are related either through physical continuity or by the transfer of membrane segments as tiny vesicles (sacs made of membrane)

• This system includes: nuclear envelope, the endoplasmic reticulum, golgi apparatus, lysosomes, various vacuoles, and the plasma membrane

Endomembrane System

Endoplasmic Reticulum

• Extensive network accounting for more than half the total membrane in eukaryotic cells

• Consists of a network of membranous tubules and sacs called cisternae

• The ER membrane separates the internal compartment of the ER, called the ER lumen (cavity) or cisternal space, from the cytosol.

• The ER membrane is continuous with the nuclear membrane

ER cont…

Two types of ER: smooth and rough

1. Smooth ER – lacks ribosomes and involved in diverse metabolic processes such as lipid synthesis, metabolism of carbohydrates, and detoxification of drugs and poisons

2. Rough ER – has ribosomes and is involved in protein synthesis

Figure 4.10a

Golgi Apparatus -- Delivery System     

• flattened stacks of membranes

• functions in collection, packaging and distribution of molecules made in the cell and used elsewhere

• front end (cis) faces the ER, and the back end (trans) faces the cell membrane

* folded stacks are called cisternae

• unprocessed proteins enter the Golgi apparatus from ER and proteins are packaged and exported to the nearest membrane

Jobs of the Golgi Apparatus              (aka Golgi Complex)1. separates proteins according to their destinations

2. modifies proteins (adds sugar and makes glycoproteins)

3. packages materials into vesicles which are exported outside the cell  -  secretion

Summary of Endomembrane System

See Handout*

Lysosomes - Intracellular Digestion Centers

• vesicles that are used to digest• contain high levels of degrading

enzymes – low pH(to "lyse" means to dissolve)

• recycle old and worn out cell parts

• "suicide sac" -  apoptosis (BONUS) digest other particles taken in by phagocytosis

http://www.youtube.com/watch?v=m6qJ69wcSnc

• found in animal cells  TAY-SACHS disease – missing an enzyme of the lysosomes that breaks down a fatty substance.  Over time this fat builds up in the brain and nervous tissue, smothering the cells.  Results in degeneration and death.

Vacuoles

Types:

1. Food vacuoles – formed by phagocytosis

http://www.youtube.com/watch?v=W6rnhiMxtKU

2. Contractile vaculoes – pump excess water out of the cell

http://www.youtube.com/watch?v=kkPiRT2ewVA

3. In plants & Fungi – Central vacuole: stores food, nutrients, water and waste…maintains turgor pressure (prefer a hypotonic state)

Mini Quiz1.  What part of the cell produces vesicles for export?

2.  What part of the cell makes proteins?

3.  What part of the cell produces ATP?

4.  What part of the cell transports materials throughout the cytoplasm?

5.  What part of the cell has a cis and a trans face?  

a.  ________________

b.  ________________

c.  _________________

d.  _________________

e.  _________________

f.  __________________

f.

What is this structure? 

Figure 4.7b

Figure 4.10a

What is this structure?

What is this structure?

Figure 4.11

Describe the processes occurring in this image.

Figure 4.13

Figure 4.16b

What is this structure?

What is this structure?

What is its function?  

Find the:

a.  Nucleolus

b.  Centriole

c.  Vesicle

d.  Smooth ER

e.  Lysosome

Summary Video Clip

http://www.youtube.com/watch?v=cj8dDTHGJBY&list=PLb3m_5kPlQwPK22qq6tBsUt_pkt4UQUvQ