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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