Lecture 1- Cell Structure Flashcards
Prokaryotic cell
No organelles
Just plasma membrane
Eukaryotic cell
Organelles
Nucleus, ribosomes, ER, golgi, lysosome
Cell nucleus
- 10% volume of cell
- DNA: all 46 pairs of chromosomes
- Double nuclear envelope (in and out )
- nuclear lamina: supports envelope + supports chromatin inside of cell
- nuclear pores: opening in nuclear membrane—> transport things in and out of cell
- nucleolus: ribosome production
- nucleoplasm: liquid surrounding organelles
Nuclear envelope
INNER:
- faces the nucleoplasm
- in contact with the nuclear lamina
- functions as a scaffold stabilizing the nuclear envelope
nuclear pores is where they come together
OUTER: - faces the cytoplasm - continuous with the ER - cytoplasmic surfaces contains ribosomes (rER)
Nuclear lamina
- thin sheetlike meshwork underneath nuclear membrane
-nuclear lamins
Type of intermediate filaments
Lamin A and B
*mutations in lamin A= progeria (get old fast)
-scaffold for nuclear envelope, chromatin and nuclear pores
Disassembles during mitosis
Nuclear pores complex (NPC)
- span the inner and outer membranes
(80-100nm) - made up of more than >50 proteins
Nucleoproteins
-3000-4000 NPC’s in a typical nuclear envelope
- Allow transport of molecules between the nucleus + cytoplasm
- ions and molecules <9 nm to diffuse freely through the pore
- molecules >9 nm must be transported by active transport
Nucleolus
- ribosome production
- rRNA is transcribed
- ribosomal subunits assembled
3 ZONES
1) Fibrillar center (FC)
- pale region
- DNA loops of 5 chromosomes
- 13, 14, 15, 21, 22
- contain rRNA genes
2) Fibrillar material (F)
- transcription of rRNA genes
3) Granular material (G)
- initial ribosomal assembly
Chromatin Structure
- Chromosomes in uncoiling
- packaged into nucleosides (complex of DNA and proteins = histones)
2 TYPES
1) Euchromatin
- lightly staining
- less condensed chromatin, more transcriptionally active
2) Heterochromatin
- densely staining
- highly condensed chromatin
- less transcriptionally active
Nucleosome
-unit of Chromatin
- macromolecular complex
(8 histone molecules-> octamer)
(2 loops of DNA wrap around the core octamer)
( beads on a string)
*in both euchromatin and heterochromatin *
Chromosome structure
- each chromosome contains specialized nucleotide sequences
- Bond specific proteins for replication and segregation
CENTROMERE
- centric heterochromatin
- Persists throughput interphase
- constricted region that holds sister chromatids together
- also the site of kinetochore formation
TELOMERE
- at the ends of chromosomes
- repeated sequences that allow the ends of the chromosomes to be replicated
REPLICATION ORIGIN
- location where DNA replication begins
Ribosomes
- made in nucleolus, leave the nucleus and enter cytoplasm
- consist of 2 rRNA subunits and associated proteins
- sites of protein synthesis (translation)
2 POPULATIONS (structurally and functionally identical)
1) membrane- bound ribosomes
2) free ribosomes
-polyribosome: many ribosomes bound to a single mRNA molecule
Protein trafficking
1) MEMBRANE BOUND RIBOSOMES
- attached to the cytoplasmic surface of the rough ER membrane (rER)
- synthesize proteins that are being translocated into the ER lumen (ER signal sequence)
- Produce:
1. Lysosomal proteins
2. Secreted proteins
3. Plasma membrane proteins
Ribosomes -> ER-> Golgi-> lysosome or secretion or plasma membrane
2) FREE RIBOSOMES
- unattached to any membrane
- synthesize all other proteins
Ex
1. Nuclear proteins
2. Mitochondrial proteins
3. Cytosolic proteins
4. Peroxisomal proteins
Endoplasmic Reticulum (ER)
- interconnected network of branching tubules and flattened sacs distributed throughout the cytoplasm
- at a site, ER membrane is continuous with the outer nuclear envelope membrane
2 REGIONS
- Smooth ER: synthesis of lipids and detoxification
- Rough ER: synthesis of proteins destined for plasma membrane, lysosomes, or secretion
- ER lumen: single, continuous, internal space -> separates from cytoplasm by the ER membrane
Rough ER
- has ribosomes attaches to cytoplasmic surface of the ER
- only mRNA molecules with an ER signal sequence bind to the rER molecules
-Abundant in cells specialized in protein synthesis
(Ex: secretory cells producing proteins for extracellular export
EM23000
1) mitochondria
2) nucleus
3) nucleolus
4) nuclear envelope
EM50000
1) ribosomes
Cresyl violet x800
1) nerve cell
Smooth ER
- region of the ER that lacks bound ribosomes
- abundant in cells specialized in lipid metabolism
(Well developed in cells that synthesize and secrete steroids)
-plays a major role in detoxification
(Ex: hepatocytes and detoxifying enzymes) (cytochrome P450 system)
-also function to sequester calcium
(Ex: muscle cells and sarcoplasmic reticulum)
Golgi apparatus
-complex of flattened, membrane enclosed cisternae
-usually located next to the nucleus and centrosome
(Location is microtubule dependent)
each stack has 2 faces
1) cis face
- entry - cis golgi network (CGN)
2) Trans face
- exit - trans golgi network (TGN)
**especially developed in secretory cells
1) plasma cells: secrete antibodies
2) pancreatic acinar cells
(Secrete digestive enzymes)
rER and golgi transport
Coatomer- Coated vesicles
- mediate bidirectional traffic between the ER and Golgi
COP-1 Coates vesicles
- retrograde transport
- CGN back to rER
COP-2 Coated vesicles
- anterograde transport
- carry newly synthesized proteins from rER to CGN
Functions of Golgi apparatus
1) post-translational modification
- glycosylation : addition of carbohydrate
- sulfation: addition of sulfur
- phosphorylation: addition of phosphate
- proteolysis: cleavage of peptide bonds
2) sorting
3) packaging
Golgi pathways
1) CONSTITUTIVE SECRETORY PTW
- basolateral (red)
- Apical (purple)
- vesicles produces for continuous secretion
Ex: fibroblasts
2) REGULATED SECRETORY PTW
- vesicles are stored and secreted with stimulus
- Ex: neurons, B cells (endocrine), and acinar cells (exocrine) of pancreas
3) LYSOSOMAL PTW
Lysosomes
Digestive organelles
-function in the controlled intracellular digestion of macromolecules
Membrane-enclosed compartments Dulles with ~40 types of hydrolytic enzymes
- LAMP, LIMP, LGP
- acid hydrolases
- require an acidic environment (low pH ~4.7)
EM27000
- lysosome (ly1)
- secondary lysosome (phagolysome)(ly2)
EM6000
Histochemical (acid phosphatase)
Targeting Proteins to lysosome
- Precursor lysosomal hydrolases are covalently modified by the addition of Mannose 6-Phosphate (M6P) in Golgi apparatus
- M6P receptor in the TGN recognizes lysosomal enzymes for transport to lysosomes
Lysosomal Storage Diseases (LSDs)
- dysfunctional lysosomes
- 1:7000 live births
- > 40 LSDs
- often result from mutations in genes that encode lysosomal enzymes
- Results:
1) accumulation of undigested products
2) disruption of normal cell function
3) cell death
Tay- Sachs Disease
- 1st LSD (warren tay 1881 and Bernard sacs 1896)
- deficiency of HEXA (beta- hexosaminidase A, alpha-subunit
- gene location (chromosome 15q24.1)
- results in the accumulation of GM2 ganglioside
- death of neurons in the brain and spinal cord
Pathways to lysosomal digestion
1) phagocytosis
2) endocytosis
3) Autophagy (self-cleaning)
Autophagy
Major cellular pathway to degrade proteins and organelles in the lysosome
- digested components are recycled and reused
- essential role in starvation, cellular differentiation, cell death, cell aging
- Ex: macrophagy
Proteasome
Proteasome-mediated protein degradation
- large protein complex
- ATP dependent
- destroys proteins without involving lysosomes
Polyubiquintion
- proteins targeted for destruction are covalently tagged with the ubiquitin protein
Destruction of abnormal proteins and normal short lived regulatory proteins
-Ex: cyclins, transcription factors, tumor suppressors
Proteasome inhibitors used as anti-cancer agents
Inclusions
Cytoplasmic or nuclear structures formed from metabolic products of the cell
Pigments
Membrane bound
1) lipofucsin
- brownish gold pigment
- generally seen in non-dividing cells
(Accumulation Over the years , wear and tear pigment)
- conglomerate of lipids, metals, organic molecules
2) Hemosiderrin
- brown pigment
- iron storage complex found in the cytoplasm
- likely formed by indigestible residues of hemoglobin
(Seen in spleen)
3) melanin
- brown pigment
Glycogen
- non membrane bound , TEM dense bodies
- single beta 20-30 nm particles or rosettes (alpha)
- storage form of glucose
- catabolism releases glucose for energy
Lipid
-non membrane bound, TEM dense
-fat droplets
(Spherical droplets of triglycerides)
(Liquid at body temperature)
- energy store and source of short carbon chains for membrane synthesis
-lipid storage diseases (lipidoses)
(Lipid droplets accumulate in abnormal amounts or locations)
Mitochondria
STRUCTURE
- 2 membranes (outer and inner)
- 2 compartments (inter-membrane and matrix)
PRIMARY FUNCTION - generate ATP 1) citric acid cycle 2) oxidative phosphorylation 3) beta oxidation of fatty acids - abundant in cells that generate and expend large amounts of energy (Ex: striated muscle cells)
Evolved from aerobic bacteria that were engulfed by primitive eukaryotic cells
- double stranded circular DNA
- maternally derives
- 13 enzymes (oxidative phosphorylation pathway)
- 2 rRNAs and 22 tRNAs
