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Pre Sgu Class > Lecture 1- Cell Structure > Flashcards

Lecture 1- Cell Structure Flashcards

1
Q

Prokaryotic cell

A

No organelles

Just plasma membrane

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2
Q

Eukaryotic cell

A

Organelles

Nucleus, ribosomes, ER, golgi, lysosome

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3
Q

Cell nucleus

A
  • 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
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4
Q

Nuclear envelope

A

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)
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5
Q

Nuclear lamina

A
  • 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

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6
Q

Nuclear pores complex (NPC)

A
  • 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
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7
Q

Nucleolus

A
  • 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

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8
Q

Chromatin Structure

A
  • 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

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9
Q

Nucleosome

A

-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 *

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10
Q

Chromosome structure

A
  • 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

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11
Q

Ribosomes

A
  • 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

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12
Q

Protein trafficking

A

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

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13
Q

Endoplasmic Reticulum (ER)

A
  • 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

  1. Smooth ER: synthesis of lipids and detoxification
  2. 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
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14
Q

Rough ER

A
  • 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

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15
Q

Smooth ER

A
  • 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)

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16
Q

Golgi apparatus

A

-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)

17
Q

rER and golgi transport

A

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
18
Q

Functions of Golgi apparatus

A

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

19
Q

Golgi pathways

A

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

20
Q

Lysosomes

A

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)

21
Q

Targeting Proteins to lysosome

A
  • 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
22
Q

Lysosomal Storage Diseases (LSDs)

A
  • 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
23
Q

Tay- Sachs Disease

A
  • 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
24
Q

Pathways to lysosomal digestion

A

1) phagocytosis
2) endocytosis
3) Autophagy (self-cleaning)

25
Q

Autophagy

A

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
26
Q

Proteasome

A

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

27
Q

Inclusions

A

Cytoplasmic or nuclear structures formed from metabolic products of the cell

28
Q

Pigments

A

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

29
Q

Glycogen

A
  • non membrane bound , TEM dense bodies
  • single beta 20-30 nm particles or rosettes (alpha)
  • storage form of glucose
  • catabolism releases glucose for energy
30
Q

Lipid

A

-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)

31
Q

Mitochondria

A

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

Pre Sgu Class (5 decks)

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