Lecture 1 (8/16) Cell Structure and Organelles Flashcards
Non-membrane bound organelles
Cytoskeleton -MT -AF -IF Proteosomes Ribosomes Centrioles and Basal Bodies Cilia, Flagella Inclusions
“CPR-CCI”
Membrane bound organelles
PM Peroxisomes Lysosomes Mitochondria ER, Endosomes Golgi Nucleus
“Please, please let me go now”
Glycoproteins will always face the?
Extracellular environment
Cytoplasm is a reducing environment and Extracellular fluid is an oxidizing environment.
Functions of the cell membrane
Structure Control movement Regulates cell cell interaction Has receptors Transport Transduces
Channels allow passage of
ions
-can be voltage, ligand, or mechanically gated.
Pumps and carriers
ions and molecules. Na/K. Ca. Glucose
Surface receptors
bind to a ligand to elicit a cellular response. Serve as signaling molecules which are kinases or are kinases themselves or are associated with kinases.
Also associated with G-proteins, cytokines, or steroid receptors.
Linkers and Structural Proteins
involved in cell-cell attachment; cell-matrix attachment
-serve as scaffolds for cytoskeleton
Major proteins in the nucleus
Replication and TF, Ribosomal proteins, histones, and fibrous proteins.
Outer nuclear membrane is contiguous with
RER
Constitutive vs facultative chromatin
C: remains transcriptionally inactive.
F: Can be decondensed and transcriptionally active, depending on cell type.
The interphase nucleus contains both transcriptionally inactive heterochromatin and also ?
Euchromatin
What goes in and out of nucleus
In:
DNA polymerase
Proteins made in the cytosol
Ribosomal proteins
Out:
mRNA to be translated
rRNA
ribosomes
Large molecules require a NLS to enter the nucleus such as
stretch of several basic amino acids such as Lysine and arginine
RNAs are transported through the NPC as ribonucleoproteins
THis requires energy provided by ATP hydrolysis. Nuclear transport proteins bring substances to the nuclear pore and facilitate movement across nuclear membrane and this requires energy provided by GTPase.
What happens in the nucleolus?
site of rRNA synthesis and ribosome assembly.
-Where rRNA and ribosomal particles come together to form the complete ribosome.
Dense fibrillar region
newly transcribed rRNA and ribosomal proteins
Granular component
assembly of RNA/ribosomal proteins into ribosomes
Metabolically active phase which may or may not lead to S phase
G1
Considered the committed step of of mitosis
S
Bulking up and proof reading phase
G2
Extended or non dividing phases
G0 and G1
Proteins that mediate apoptosis
caspases
Caspases begin to
digest the DNA as well as cytoplasmic proteins and organelles
Ribosomes can associate with ER membranes if the nascent polypeptide contains?
A signal sequence
As many as 11-15 ribosomes can be on one mRNA. This structure is called a?
polyribosome.
A free polyribosome with no signal sequence can go to
Mitochondria, Peroxisomes, Nucleus. (No sequence needed)
ER bound polyribosomes target the protein to
Golgi , SV, Lysosomes, and protein either becomes part of membrane or secreted from the cell.
Functions of the RER
Synthesis
Transport
Storage
Detox
What binds to ER signal sequence?
SRP -signal recognition particle
and then binds to docking protein.
Which proteins have an internal signal sequence?
Proteins that span the lipid bilayer.
In the ER…
New proteins move into ER cisternae
Mannnose rich oligosaccharides are added to specific asparagine residues (N-linked)
Proteins are folded
Disulfide bonds are formed between cysteine residues
Cis Golgi events
Vesicle movement from RER through golgi network is promoted by COPII
Similarly , COPI controls retrograde vesicle movement
Mannose 6-phosphate is added to future lysosomal enzymes
N linked oligosaccharides are trimmed and other sugars are added
Medial golgi events
New glycosylation occurs on -OH groups of some lipids and Serine and threonine residues (O-linked).
N-linked oligosaccharides on proteins are modified further.
Glycoproteins and glycolipids are sorted into specific vesicles.
Trans golgi events
Sialic acid is added as the terminal sugar to certain oligosaccharides
Sulfation of tyrosine residues and some sugars
Specific vesicles with different destinations are separated and sorted.
Where are sugars added ?
ER and modified in the golgi
Default from the TGN is the
Plasma membrane
Proteins destined for the lysosome contain a recognition site consisting of ?… and delivered by vesicular transport from the TGN.
Phosphorylated mannose … M6P
Material is delivered to the lysosomes in two ways.
- Vesicular transport by the TGN
2. By vesicles derived from the PM.
3 types of alternative transport pathways to the lysosome ?
Phagocytosis (bulk material-bacteria, cell debris)
Endocytosis
Autophagy
In receptor mediated cytosis, what helps “direct traffic”
Coat proteins
What happens to the receptors and ligands in the case of LDL?
Receptor recycles
Ligand degraded
What happens to the receptors and ligands in the case of transferrin?
Both receptor and ligand are recycled
What happens to the receptors and ligands in the case of EGF?
Both receptor and ligand are degraded
What happens to the receptors and ligands in the case of IgA
Both receptor and ligand are transported (“transcytosis”)
Where are peroxisomal proteins synthesized?
cytoplasm - they are transported into the organelle using a specialized targeting amino acid sequence.
One major function of the peroxisomes is?
Oxidation of LCFA, but the energy generated is not used to synthesize ATP
Hydrogen peroxide is broken down by?
Catalase
Where is the proteasome located?
Cytoplasm and the nucleus
Proteins that are destined for destruction are tagged with a 76 AA peptide called ?
Ubiquitin
Degradation via the secretory pathway ends up at the
Lysosome
Degradation via the cytosol ends up at the
Proteasome
All of the MT, AF, and IF are held together by
non-covenant bonds
Functions of the cytoskeletal system
Pulls chromosomes apart Guides intracellular traffic Supports the PM Swim and crawl (sperm) Muscle contraction Maintains diversity
Microtubules
Mechanical reinforcement
Tracks for motor proteins
Chromosomal moment during mitosis
Tracks for movement along axons (neurotubules)
** Cilia and Flagella
Organized around centrioles or basal bodies.
Tubulin is a heterodimer
AF
cross linked, anchored to the PM to reinforce the surface of the cell.
What supports microvilli?
Actin fillaments
-Genetic defects in the actin binding protein, dystrophin cause most of the common forms of muscular dystrophy.
Intermediate filaments
strong and flexible.
All IF are related to the ? molecule.
Keratin
IF link the
PM to the nucleus
some reinforce the nuclear envelope
Genetic defects in certain IF cases a severe ?
Blistering of the skin, along with other disorders.
Inclusions
Glycogen Lipids (stores to make hormones on demand when needed because storing hormones would diffuse into the cells when not supposed to because they are lipid soluble). Lipofuscin Hemosiderin Melanin Crystals
