Cells and Mechanisms of Diseases Flashcards
Physiology
Study of body function
Pathophysiology
studying physiological aspects of disease
Major components of the cell:
A. Plasma Membrane
* encloses the cytoplasm
* outer boundary of the cell
* controls movement of substances into and out of the cell
phospholipids, cholesterol, proteins, and carbohydrates
B. Cytoplasm
* internal liquid of the cell (aka cytosol)
* contains organelles
C. Nucleus
* controls reproduction & protein production
Functions of Plasma Membrane
➢Doesn’t just enclose cell
➢Provides shape and strength
➢Separates internal content from interstitial fluid which surrounds cells
➢Membrane constituents act as receptors, carriers, channels or pumps
➢Extensions of membrane move the cell, move objects past the cell or aid in absorption
➢Cilia, microvilli, flagellum
Structure of the Plasma Membrane
Composition:
➢2 phospholipid layers
➢Cholesterol: helps keep the membrane rigid and stabilizes phospholipid
Proteins are receptors for other molecules or cells
* Part of the immune system
* Recognition of self: HLA system (HLA = Human Leukocyte Antigen; MHC = Major Histocompatibility Complex)
Protein & Carbohydrate chains on the surface act as antigens or ‘markers’
Transport of Fluid & Molecules
Passive Transport
o No energy required
✓Diffusion
✓Osmosis
✓Filtration
Active Transport
➢Requires energy
➢Breakdown of ATP & released energy
needed
✓Ion pumps
✓Phagocytosis
✓Pinocytosis
Passive Transport: Diffusion
Diffusion: movement of PARTICLES
Diffusion: movement of particles through a
membrane from an area of high concentration to an area of low concentration; that is, down the
concentration gradient e.g., movement of carbon dioxide out of all cells; movement of sodium ions into nerve cells as they conduct an impulse
OSMOSIS:
facilitated diffusion
movement of water from high concentration to low concentration
Passive Transport: Filtration
movement of water and small solute particles, through a filtration membrane; from high pressure to low pressure - hydrostatic (more pressure from where the cells are leaving from)
e.g., in the kidney, water and small solutes move from blood vessels but blood proteins and blood cells do not, thus beginning the formation of urine.
Active Transport: Ion Pumps
special membrane protein that moves ions (charged molecules) across the membrane
high concentration to area of low concentration
needs energy
What happens when there are ‘problems’
with the cell membrane?
Skeletal proteins missing from red cell
membrane = hereditary spherocytosis or
elliptocytosis = decreased red cell survival
Wrong blood type transfused = recipient
antibodies destroy donor red blood cells
Cystic Fibrosis – chloride ion pump is missing
* Cells that require chloride die
* increased cell debris cause thick secretions
* Increased mucus
* Digestive problems
Cholera bacteria infect intestinal epithelium
Cause chloride & water to leave cell
results in severe diarrhea & dehydration
Cell Organelles
Lysosomes-* contain lytic enzymes that can destroy proteins , carbs, NA,
peroxisomes - like lysosomes but have peroxides detoxify the body found in the liver
e.g. * Phagocytosis
* Cytotoxin release
Golgi apparatus- look like stacked bowls cisternae package, process, transport proteins
er - rER with ribosomes produce proteins - found in endocrine glands
sER no ribosomes lipid synthesis and detox - liver
What happens when the organelles are
abnormal?
Example - Chediak-Higashi
disease: lysosomal trafficking
regulator gene mutation
* Large lysosomal granules which do not
function correctly
* Bacteria still phagocytosed by the cell, but the lysosomes don’t function properly: they don’t degranulate, so the bacteria are not destroyed
* Phagocytosis is impaired & death by infection is common
Nucleus
Nucleolus
* Critical in protein formation
* Production of ribosome subunits (rRNA)
* Move to cytoplasm for protein production - structural and functional
Chromatin
* Chromatin granules are proteins with DNA wound around
* Tightly coiled during cell division: chromosomes
Euchromatin
- Diffuse, uncondensed: loosely coiled
- Active portion of nucleus
- Area of RNA transcription
- Stains paler purple in Wright’s stain
- Immature cells actively producing
protein - Usually have nucleoli
Heterochromatin
Condensed, clumping pattern.
* Stains dark purple in Wright’s stain
* oldest, most mature cells no
longer dividing or
* Inactive stage
Protein Synthesis
- Protein synthesis begins with transcription, a process in which an mRNA molecule forms along one gene sequence of a DNA molecule within the cell’s nucleus. As it is formed, the mRNA molecule separates from the DNA molecule.
- The mRNA transcript then leaves the nucleus through the large nuclear pores
- Outside the nucleus, ribosome subunits attach to the beginning of the mRNA molecule and begin the process of translation
- In translation, transfer RNA (tRNA) molecules bring specific amino acids—encoded by each mRNA codon—into place at the ribosome site. As the amino acids are brought into the proper sequence, they are joined together by peptide bonds to form long strands called polypeptides. Several polypeptide chains may be needed to make a complete protein molecule.
No Iron?
e.g. low iron → iron deficiency anemia, may
be acquired or nutrition related
No Globin?
e.g. thalassemia (inherited)
Phenylketonuria or PKU
Deficiency of the enzyme PAH
(phenylalanine hydroxylase) results in high levels of phenylalanine in the blood.
➢Mental impairment results if the
condition is not recognized.
✓Basis of first Newborn
Screening
✓Special diet from birth
prevents effects of disease
Cell Division
Nuclear membrane & nucleolus disappear
during Mitosis as cell duplicates DNA and
divides
Interphase and Mitosis
Interphase is divided into G1, S, and
G 2 phases.
* Cell growth occurs during G1.
* DNA synthesis or replication in S
* Cell prepares for mitosis in G2
* The cells may also enter a quiescent
phase called G0, where the cell
functions but does not divide.
Apoptosis:
programmed cell death
* Mechanism by which abnormalities of cell
division are excluded from proliferating,
over produced cells are removed or
damaged cells die
Example: Apoptosis of an epithelial cell:
* Cell age or an abnormal cell
* This is a NORMAL PROCESS!
* Initiated by a variety of stimuli
* Proteolytic cascade results in cell death
* Procaspase in cells become active enzymes
→ caspases and result in cell ‘suicide’
Critical cell cycle checkpoints:
cell will either continue through the cell cycle or undergo
apoptosis.
1. G1 checkpoint is before S phase and DNA replication:
cell stalls here while any DNA repair takes place
2. G2 checkpoint: after DNA replication: if replication was normal the cell proceeds to mitosis
Cell Cycle Errors
Genes & their protein products control Cell
Cycle
➢e.g. p53 gene protein detects DNA
damage in G1 & can trigger apoptosis
➢Mutated p53 gene can result in
uncontrolled cell proliferation
