Download Chapter 4 - selu moodle

Chapter 4
Vocabulary:
Cell Theory
Prokaryote
Eukaryote
Organelle
Plasma membrane
Nucleus
Ribosome
Endoplasmic reticulum
Golgi apparatus
Lysosome
Mitochondria
Chloroplast
Cytoskeleton
Endosymbiosis
Outline
4.1 Cell Theory
Cell Theory:
1. All living things are composed of cells
2. Cells are the basic functional unit of life
3. All cells come from pre-existing cells
Cell size is limited by surface area : volume ratio
Flow of nutrients in and waste out is not fast enough to keep up with the
metabolic activity of the cell. Cell signaling impaired. Membrane vastly important
Basic Requirements to be a cell:
1. Genetic material (DNA)
2. Cytoplasm (chemical reactions)
3. Plasma membrane
4.2 Prokaryotic Cells
Smaller, simpler
Metabolically diverse
Bacterial domains:
Archaebacteria and Eubacteria
Before the nucleus
Nucleoid region (one circular chromosome)
Some bacteria carry plasmids (small circles of DNA with non-essential
genes like antibiotic resistance) We use plasmids to manipulate cells.
No membrane bound organelles
Have ribosomes for protein synthesis
No internal membrane (all metabolic activity occurs in the cytoplasm and at the
cell membrane)
No true cytoskeleton
Use flagella for movement
Use pili for attachment and to exchange genetic information
Cell walls made of peptidoglycan (specific to bacteria) antibiotics stop formation of
peptidoglycan. When you get sick you probably have about 1million cells infecting your
body. Some of these cells double every 20min. Antibiotics don’t allow for the formation
of peptidoglycan so the old ones die off and the new ones can’t make it. Without it they
are not viable cells. Antibiotics reduce bacteria by decimals not kill all at once. If you
don’t finish antibiotics cells can make peptidoglycan again and re-infect.
Gram positive bacteria have lots of peptidoglycan. These infections can be treated with
penicillin because it stops the formation of peptidoglycan. Without an adequate cell wall
the bacteria don’t survive.
Gram negative bacteria don’t have a large layer of peptidoglycan so penicillin isn’t as
effective against them. Instead they are treated with mycin which stops bacterial
ribosomes (which are slightly different from eukaryotic ribosomes). Without ribosomes
the bacteria can’t make necessary proteins and they don’t survive.
4.3 Eukaryotic cells
Larger (10X)
Fungi, protists, plants, animals
True nucleus – DNA is housed in a membrane-bound nucleus
Membrane bound organelles (Compartmentalization of function)
Nucleus: Houses DNA
Like a fortress with double bi-layers and envelopes and guard proteins (pores)
Site of transcription (DNA  mRNA)
Components of ribosomes are made in the nucleolus
Ribosomes: rRNA and protein complex that translates proteins
Free ribosomes synthesize cytoplasmic, nuclear, mitochondrial and other
organelle proteins.
Membrane-associated ribosomes synthesize proteins for the membrane and
endomembrane system and proteins for export from the cell
4.4 Endomembrane System
Rough ER: studded with ribosomes
synthesize proteins for the membrane and endomembrane system and proteins for
export from the cell
modify proteins with addition of glycoproteins
Smooth ER: no ribosomes, contains embedded enzymes
Synthesis of carbohydrates, lipids, steroid hormones and membrane lipids
Stores calcium ions for signaling
Neutralizes toxins
Golgi apparatus: collects, packages, modifies and distributes molecules
Lysosomes: breakdown proteins, lipids, carbs and nucleic acids
Recycle organelles, enzymes, etc
Digest pathogens
Microbodies
Peroxisomes: oxidize fatty acids
Vacuole: help cells maintain tonicity
Specialized for different functions in different cells
4.5 Mitochondria and Chloroplast
Mitochondria: produces ATP from macromolecules by oxidative metabolism
Chloroplast: produces food for cells via photosynthesis
Endosymbiant Theory:
Theory proposed by Lynn Margulis in 1967 that explains how we go from prokaryotic
cells with no organelles to eukaryotic cells with all these organelles.
Early Earth had little or no free O2
Evolution of photosynthetic organisms changed the composition of the Earth’s
atmosphere
Cells evolved in response to the new O2 and took advantage of it by producing more
energy using it (because it has a better redox potential)
Aerobic respiration
Predatory cells could have engulfed these cells that were capable of performing aerobic
respiration. If cells were not digested eventually the host might gain some benefit
from the ATP produced. Likewise, the prey would benefit from being sheltered
and fed.
Prey became mitochondria
Which today has its own single circular genome and ribosomes
Mitochondria also replicate independently of the host and have a few DNA “words” that
are unique to them.
Can use mitochondrial DNA to determine eukaryotic relatedness based on similarity
(because only passed on by the mother)
Possible that the bacteria they originally were is Rickettsia prowazekii which causes
typhus (fever, chills, pain, rash from rat’s flea bites or body lice – rare in US)
Chloroplasts have a similar story only they allowed hosts to photosynthesize. Different
chloroplasts in different organisms just like diff bacteria – possible this
engulfment happened more than once!?!
Proof of Endosymbiant Theory:
Same size as bacteria
Double membranes
Circular DNA
Prokaryotic ribosomes
A few “words” in DNA is different from near universal code. First amino acid
added is formyl-methionine; not methionine.
Replicate independently
No histones associated with DNA
There are still bacteria so NOT all organisms ingested others. Some parasitic eukaryotes
have lost certain organelles (specifically mitochondria) because they don’t need to make
energy; they just sap it from the host. Protists with no mitochondria include
Microsporidia, Entamoeba histolytica, Giardia intestinalis. All are found in contaminated
drinking water and lead to diarrhea, upset stomach, cramps and dehydration.
4.6 Cytoskeleton
Functions:
Reinforce
Organize
Move things around
Actin filaments (Microfilaments) – thinnest
Cellular movement
Microtubules – keeps organelles and other structures in place and also facilitates their
movement
Can be built up or broken down at will – not permanently stable
Use motor proteins
Intermediate filaments – the most stable cytoskeleton components
Used to strengthen and maintain cell shape
Motor proteins are fueled by ATP
Use kinesin and dynein
Important for contraction of muscle
Important for plants so chloroplasts can be at the best absorbing point.
4.7 Extracellular Structures and Cell Movement
Flagella: 9+2 structure attached by a basal body used to propel organisms forward.
Cilia: 9+2 structure of numerous hair-like projections that beat in synchrony.
Cell Walls:
Plants and protists use cellulose
Fungi use chitin
Animals do not possess. Instead they crease an extracellular matrix of
glycoproteins
4.8 Cell-To-Cell Interactions
Surface markers identify cells
Tight junctions connect plasma membranes of cells forming a sheet (These are water
tight)
Adhering junctions occur in places exposed to continual stretching (heart and skin).
(Anchored to ECM)
Gap junctions connect cells directly to increase speed of flow between them like in the
heart. (Open channels)
Plasmodesmata are gap junctions in plants
This chapter is pretty basic cell anatomy. Make sure you cover surface area : volume
constraints. You can skip microscopes.
I have included some additional notes on prokaryotes. When I cover prokaryotes I
generally put a picture on the overhead and draw all over it as I discuss the anatomy.
Don’t worry too much about difference between archea and Eubacteria.
As far as Eukaryotic organelles students should get a feel for how a cell is
interconnected; how the organelles work together like departments in a company.
Mitochondria and chloroplast are important to introduce since we will see these
organelles again in respiration and photosynthesis. I also included some extra information
on the Endosymbiant Theory which links prokaryotes to eukaryotes. Table 4.2 lists all
relevant eukaryotic organelles.
In 4.6 talk about the 3 components of the cytoskeleton and what they do, but don’t worry
about how they do it. 4.7 you can talk about structures and types of movement, but in a
by the way sort of way. I do not have time to cover 4.8 other than to mention the surface
markers and the junctions.