Histology 1 - Cell Cytoplasm and Cell nucleus

Describe the characteristics of the plasma membrane

- lipid bilayer with proteins (integral and peripheral)

- amphipathic phospholipids

What are the 2 faces of the plasma membrane called?

extraplasmic (outside- facing)

protoplasmic (inside-facing)

What are the different kinds of integral membrane proteins?

1. Pumps

2. Channels

3. Receptors

4. Linkers

5. Enzymes

6. Structural

What are the 3 ways of transport across the plasma membrane?

1. Simple diffusion

2. Carrier Proteins (active or passive; highly selective)

3. Channel proteins (ion-selective, regulated by membrane potential)

What usually goes into the cell via simple diffusion?

small hydrophobic molecules

what usually goes into the cell via carrier protein?

larger molecules (ex. glucose)

- conformational change

What usually goes into the cell via channel proteins?

ions

What are the examples of vesicular transport?

1- Endocytosis (pinocytosis, phagocytosis, receptor-mediated)

2- Exocytosis (constitutive or regulated)

Overview of pinocytosis

"cell drinking"

nonspecific

small proteins and fluid

Overview of phagocytosis

- only specialized cells (macrophages and neutrophils)

- engulf cell debris and bacteria

- requires rearrangement of the actin cytoskeleton

- forms phagosomes

What are the steps of receptor-mediated endocytosis?

1- cargo protein binds to cargo receptor

2- formation of the coated pits with adaptin + clathrin

3- formation of coated vesicle (invagination of the pit, pinching off into the cell)

4- coated vesicle enters the cell

5- vesicle uncoats itself (adaptin and clathrin come off and are recycled into cytoplasm)

6- uncoated vesicle is ready for further processes

What are the 2 proteins involved in helping vesicle formation during receptor-mediated endocytosis?

adaptin and clathrin

What is an endosome?

vesicle that pinches off from the membrane during endocytosis

- membrane-bound intracellular sorting organelle

- generally becomes a lyososme

Describe the stages of a endosome becoming a lysosome

early stage - sort and recycles proteins (pH 6.2-6.5)

late stage - pre-lysosome (pH 5.5)

Lysosome - degradation (pH 4.7)

Why are lysosomes at a very low pH compared to physiologic pH?

- proteins are usually degraded here by various lysosomal enzymes

- these enzymes can only function at a low pH - so that if the lysosome were to rupture and the enzymes were released into the cell, the cell would not become digested

What is a lysosome?

Digestive organelle with tough membranes that resist digestion

What are some of the enzymes that can be found in a lysosome?

proteases, lipases and phospholipids, glycosidases, etc.

What are the 4 pathways that lead to intracellular digestion in lysosomes?

1. receptor-mediated endocytosis

2. pinocytosis

3. Phagocytosis

4. autophagy

Tay-Sachs disease symptoms

loss of vision and hearing

muscle atrophy due to loss of nervous tissue

early death (often by 5 y)

Tay-Sachs disease enzyme deficiency

Hexosaminidase A

Tay-Sachs disease substrate build-up

GM2 ganglioside in neurons

I-cell disease symptoms

skeletal abnormalities

hepatomegaly

mental retardation due to abnormal cellular architecture

early death (often by 8 y)

I-cell disease enzyme deficiency

N-acetylglucosaminyl-1-phosphotransferase

I-cell disease substrate buildup

lysosomal hydrolases not phosphorylated in Golgi, get secreted instead

Niemann-Pick disease (type A) symptoms

hepatosplenomegaly

neurodegeneration

progressive wasting due to sphingomyelin accumulation in all cells of the body

early death (often by 3 y)

Nuemann-Pick disease (type A) enzyme deficiency

Spingomyelinase

Nieman-Pick disease (type A) substrate buildup

sphingomyelin

Gaucher disease symptoms

affects the spleen, liver, lungs, bone marrow due to accumulation of glucosylceramide in cells of the macrophage-monocyte system

Gaucher disease enzyme deficiency

B-glucocerebrosidase

Gaucher disease substrate build up

glucosylceramide

What are peroxisomes?

oxidative organelle

- single membrane-bound with proteins synthesized on cytoplasmic ribosomes

- contains catalase and other peroxidases (breaks down hydrogen peroxide)

- abundant in liver and kidney cells

main roles of peroxisomes

- B-oxidation of fatty acids

- Detoxification of ethanol

- Synthesis of plasmalogens (maintain membrane integrity, esp. in CNS)

Zellweger syndrome

Nonfunctional peroxisomes

CNS demyelination; early death

What are the 2 subsets of exocytosis?

constitutive or regulated

Constitutive exocytosis

product is released from the cell when it is made

- ex: antibodies

Regulated exocytosis

product is secreted from the cell when signal is received

- ex: endocrine and exocrine cells, neurons (hormones and NTs)

What is the sequence of organelles traversed in the trafficking of secreted proteins?

1. Nucleus transcribes mRNA

2. rER translates mRNA --> protein

3. proteins are transported to sER via vesicle

4. Golgi complex sorts and processes proteins

5. secretory proteins/other products can be exocytosed

Describe the rough endoplasmic reticulum (rER)

- contains ribosomes

- continuous with nuclear envelope

- involved in the synthesis of secreted and membrane proteins

- highly developed in secretory cells

ex: osteoblasts, glandular cells (antibody-secreting cells)

Describe the smooth endoplasmic reticulum (sER)

- No ribosomes

- Tubular in appearance

- Abundant in cells that function in:

1. lipid metabolism

2. detoxification

3. steroid synthesis

What is the role of the Golgi apparatus?

Post-translational modification, sorting and packaging of proteins

What are the characteristics of mitochondria?

- generation of energy (ATP) - oxidative phosphorylation, TCA, b-oxidation of FAs

- Derived from prokaryotic cells

- 2 membranes, 2 compartments

NOT present in RBCs or terminal keratinocytes

- Many in oxidative skeletal muscle fibers

What are the major categories of non-living inclusions?

- secretory granules

- stored energy (ex: glycogen, fat)

- pigments (hemoglobin and melanin)

- crystals (those in Sertoli and Leydig cells

Which organelle is expected to contain active proteases, lipases, nucleases and glycosidases?

lysosome

What are the 3 components of the cytoskeleton?

microtubules (thick), actin (thin), intermediate filaments (involved in tight junctions)

What is the main function of microtubules?

transportation and movement

What is the main function of actin?

membrane structure

motility

What is the main function of intermediate filaments?

mechanical strength

involved in tight junctions

Microtubules structure

y-tubulin ring (at (-) end) (near centrosome)

a- and B- tubulin molecules (bind GTP/GDP)

growing (+) and non-growing (-) ends

What do microtubules do in the cell?

- vesicular transport

- movement of cilia and flagella

- alignment, separation of chromosomes during cell division

- motor proteins aid in transport (kinesins+ and dyneins- )

What is the role of the centrosome?

align mitotic spindle during cell division

involved basal bodies of centrioles

Basal bodies

centrioles forming the bases of cilia and flagella

microtubules extend from here

Centrioles

central point of MTOC assembly

9 sets of microtubule triplets

Organization of centrosome

2 centrioles paired at 90 degrees from each other

Kartagener's syndrome

immobilization of cilia (problems with formation of microtubules)

- infertility, bronchiectasis, situs inversus

Chemotherapy in relation to microtubules

taxol: prevents depolymerization

vinblastine and vincristine: inhibit formation of mitotic spindle for cell division

Structure of actin

thinnest filament

spontaneously assembles

requires energy (ATP)

flexible - allows for movement of the cell membrane

What are the functions of actin filaments?

- maintain cell shape and structure

- microvilli

- anchorage to the EC matrix and cell movement

- extension of cell processes

- locomotion

Phalloidin

poisonous mushroom compound that prevents de-polymerization by binding to F-actin

Cytochalasin B and D

- prevents polymerization of actin

- inhibits lymphocyte migration, phagocytosis, and cell division

Intermediate filaments

- play a structural role

- do not continuously reform

- cell-cell and cell-matrix junctions

- classes:

1. cytoplasm (keratins, vimentins, neurofilaments)

2. Nuclear (lamins)

Alcoholic liver cirrhosis

accumulation of keratins

mallory bodies

Alzheimer's disease

neurofilaments

neurofibrillary tangles

Which of the following is the cytoskeletal element that intracellular vesicles are transported along?

microtubule

The drug taxol does which of the following:

A. binds to F-actin to prevent depolymerization

B. binds to F-actin to prevent polymerization

C. inhibits formation of the mitotic spindle

D. prevents microtubule depolymerization

prevents microtubule depolymerization

What is the function of the nucleolus

rRNA synthesis, riboome assembly, regulation of the cell cycle

- Nucleostemin-p53 binding protein

What is nucleostemin?

proteins that regulates cell cycle and influences cell differentiation

- may play a role in malignancy

What organelle can be a target of viruses and why?

nucleolus (regulates the cell cycle)

- viruses can hijack the cell cycle to control viral replication

What is the difference between endosomes and lysosomes?

endosomes = transport

lysosomes = digestion

What are the components of the nucleus?

nuclear envelope, nuclear lamina, nucleolus, chromatin

Describe heterochromatin

Dark staining, more condensed (tightly packed) not being actively transcribed

Describe euchromatin

light staining, less condensed; transcriptionally active

What is chromatin?

DNA and its structural proteins

packaged to fit in the nucleus

forms chromosomes

What are the organelle features of cells that produce a lot of proteins?

rough ER and prominent nucleolus

Describe the structure of the nuclear envelope

2 bilayer membranes with a perinuclear space

perinuclear space is continuous with the endoplasmic reticulum

What is the nuclear lamina?

scaffolding for the chromosomes and the nuclear pores

A netlike array of protein filaments lining the inner surface of the nuclear envelope

- helps maintain the shape of the nucleus

what are the clinical correlates associated with impaired nuclear lamina architecture?

Progeria (lamin A/C)

Emery-Dreifuss muscular dystrophy (EDMD; lamins, lamin receptors, emerin)

When do we see condensed chromosomes?

metaphase

What are the components of a condensed chromosome?

2 chromatids (cell division)

Telomeres (shorten with each cell division)

Telomerase

repeatedly adds nucleotide sequences to the telomere ends

- role in oncogenesis (formation of malignant cells)

Barr body

- in individuals with 2 X chromosomes, one X is repressed and stays tightly condensed

- often found adjacent to nuclear envelope

What are the 3 categories of cells in terms of cell renewal capacity?

Static (TD), Stable, renewing

What are static cells?

no longer dividing

CNS (neuronal cells) and cardiac muscle

What are stable cells?

divide when needed/signaled to

smooth muscle and endothelial cells

hepatocytes

What are renewing cells?

slow - fibroblasts, epithelial cells of the eye lens

fast - blood cells, epithelial cells

What are the phases of the cell cycle?

Interphase: G1, S, G2

Mitosis: M

Other:

- G0 (quiescent/stable cells) and G(TD)

Mitotic issues

- malfunction of any of the DNA damage checkpoints or the spindle assembly checkpoint in early mitosis

Failure to arrest the cell cycle before or at mitosis results in aberrant __________________.

chromosome segregation (aneuploidy, tumor cell development)

What can malformation at the G1 restriction checkpoint result in?

malignant transformation

What 2 protein-complexes is the cell cycle regulated by?

cyclin

cyclin-dependent kinase (cdks)

Mitosis overview

cell division

- creates 2 daughter cells with the same chromosome number (n) and DNA content (d)

- cell goes from 4d before division to 2d after division

Meiosis overview

Gametes

- reductional division to 1n

- males = 4 spermatids

- females = 1 oocyte and 3 polar bodies

What are the 2 forms of cell death

necrosis and apoptosis

Necrosis

accidental cell death

cell lysis and swelling

Apoptosis

programmed cell death

phagocytosis removes debris

20x faster than mitosis

Apoptotic bodies

condensation of nuclear material

Where is ribosomal rRNA made?

nucleolus

During which cell cycle phase is DNA duplicated in preparation for cell division?

S phase

Which cell division process yields cells with the same number of chromosomes and same DNA content as the parent cell?

Mitosis

Appropriate progression to the next phase in the cell cycle is regulated with the enzymatic activity of which of the following?

A. Cyclins

B. Cyclin-dependent kinases

C. Proteases

D. Barr bodies

E. Apoptotic bodies

Cyclin-dependent kinases