Cytology Flashcards
(32 cards)
Name 2 functions of membranes in a eukaryotic cell.
Provide pertinent nomenclature.
- Form a barrier between cell and external environment
- Subdivide the cell into the compartments (organelles) that are then able to maintain novel interior environments
What are the 3 basic components of a membrane?
How are membranes visualized?
- Lipids
- Proteins
- Carbohydrates
Membranes cannot be visualized with light microscopy but can be visualized with electron microscopy (7nm thin)
Describe a key characteristic of membrane lipids with regards to affinity for water?
How does this affect how membrane lipids interact with one another, and what do they form because of this?
Membrane lipids are amphipathic with uncharged, hydrophobic tails; and charged, hydrophilic heads.
This causes the formation of a lipid bilayer. Hydrophilic heads facing out, and hydrophobic tails facing in. This forms a hydrophobic center where membrane proteins can anchor.
Describe the fluid mosaic model.
For what molecules is the membrane permeable?
What molecules will require transport proteins because they will not pass freely.
The fluid mosaic model is the interpretation of the molecular organization of membranes to include a hydrophilic outer layer and hydrophobic center where proteins can anchor.
Permeable: small, uncharged
Inpermeable: large, ions
What categories can we group membrane proteins into?
- Structure
Integral (ex: transmembrane proteins) - hydrophobic region embedded into hydrophobic core
Peripheral - not embedded, attach to either integral proteins or hydrophilic heads
- Function
Transport proteins (channel proteins, carrier proteins, pumps)
Receptors
Structural or anchoring proteins - attach cell to surroundings
Describe the difference between the three types of transport proteins.
- Channel proteins - form pores for passive diffusion (ion-selective)
- Carrier proteins - drag molecules through membrane by hiding in cleft
- Pumps - use ATP to actively pump ions through the membrane
Describe how carbohydrates are involved in cell membranes.
What do they attach to? What does this form?
How does this appear on an electron microscope and what is the name for this coating?
Carbohydrates, mostly oligosaccharides, attach to extracellular domains of proteins and lipids to form glycoproteins and glycolipids respectively.
The large number of these carbohydrates attached to the outer surface looks like a “fuzzy coating” on electron microscopy. This outer “fuzzy” coating is called the glycocalyx.
Describe the functions of particles and inclusions.
What are the two main types?
Particles and inclusions are used for synthesis and storage.
- ribosomes
- Glycogen particles
Describe the structure and function of ribosomes.
Where do ribosomes exist in eukaryotic cells? What work is done at each of these locations?
Describe a polysome.
Ribosomes consist of a small subunit and large subunit made of ribosomal RNA and specialized proteins. They work to catalyze protein synthesis by bringing mRNA and tRNA together.
- Free ribosomes - most cellular proteins synthesized here, including 80% mitochondrial proteins
- Mitochondrial ribosomes - hand 20% of mitochondrial proteins
- Ribosomes bound to rough endoplasmic reticulum - proteins for Golgi apparatus, lysosomes, secretory granules, and plasma membrane
A polysome is a string of ribosomes connected to a single mRNA molecule - this occurs during protein synthesis
Describe glycogen particles.
Storage form of polysaccarides
Describe the general morphological characteristics of endoplasmic reticulum.
What are the morphological differences between smooth ER and rough ER?
Where would you be more likely to find prominent smooth ER versus rough ER?
General endoplasmic reticulum is made of anastomoses tubules and cisternae (flattened, pancake-like vesicles).
Smooth ER
- no ribosomes
- more tubular in appearance
- more prominent in steroid secreting cells and liver cells
- present in muscle tissues as the sarcoplasmic reticulum
Rough ER
- ribosomes, rough appearance: more ribosomes on cytoplasmic side
- mostly cisternae
- more prominent is protein secreting cells
Describe the functions of smooth endoplasmic reticulum.
Describe the functions of rough endoplasmic reticulum.
Smooth endoplasmic reticulum
- lipid and steroid metabolism: membrane synthesis and recycling
- detoxification: contains enzymes that can detoxify carcinogens, pesticides, etc…
- glycogen metabolism
- contraction in muscle cells: storage and transport of Ca+ as sarcoplasmic reticulum
Rough endoplasmic reticulum
- synthesis of proteins destined for export
- synthesis of proteins for Golgi apparatus, lysosomes, and plasma membrane
Describe the structure of the Golgi apparatus including the polarization.
Describe the two basic functions of the Golgi apparatus.
Series of stacked, flattened, membrane-limited cisternae and tubular extensions.
Cis golgi is the side receiving proteins from the RER.
Medial golgi consists of the middle cisternae.
Trans golgi is the cisternae from which mature proteins are transported.
Functions
- Posttranslational modification of proteins
- Sorting and packaging of proteins
Describe the functions of the Golgi apparatus in detail including locations.
What are the three destinations of proteins leaving the golgi?
1. Modifications of proteins.
- adding and removing sugar residues, sulfate, or phosphate groups
- early stages in cis golgi, intermediate steps in medial golgi, and final modifications in trans golgi
2. Sorting and packaging proteins into transport vesicles: proteins bear specific signal sequences which direct them to 1 of 3 destinations
- Secretory vesicles: stored proteins and other products in secretory vesicles undergo maturation, mature secretory vesicles then fuse with plasma membrane to release into extracellular space
- Lysosomes: involved in digesting material taken up from outside and degradation of senescent organelles
- Constitutive pathway: proteins in trans golgi not going to secretory vesicles or lysosomes are sorted into small vesicles and transported directly to plasma membrane to fuse with membrane (integral membrane proteins and proteins secreted into extracellular space)
Describe the structure, function, and characteristics of lysosomes.
What is the sorting signal that directs proteins from the Golgi to lysosomes?
When this sorting signal pathway is disrupted what disease does this cause?
Spherically organelles of variable size produced by golgi
Digest material from outside and degradation of senescent organelles.
Expect low pH and presence of hydrolytic enzymes.
Mannose-6-phosphate is the sorting signal. When this mutates lysosomal proteins are secreted into the intercellular space resulting in I-cell disease (mucolipidosis)
Describe the three stages of lysosomes.
- Primary lysosomes: not yet received substrates
- Secondary lysosomes: fusion of primary with target
- Lipofuscin granules (residual bodies): senescent lysosomes with undigestible materials
Describe structure and function of peroxisomes. What would you expect to find in a peroxisome?
Small, membrane bound organelle
Oxidizes large range of organic substances including very long chain fatty acids, and conversion of ethanol to acetaldehyde. Also breaks down hydrogen peroxide
Containes oxidative enzymes, specifically catalase
Describe Zellweger syndrome and Adrenoleukodystropy.
Which organelle when dysfunctional causes these disorders?
Peroxisomes
1. Zellweger syndrome
- mutation of proteins responsible for proper transport of peroxisomal enzymes from cytoplasm (synthesized on free ribosomes) to the peroxisomes
- peroxisomes lack necessary enzymes
- improper formation of myelin sheath, affects brain development
- death before 6 months of age
2. Adrenoleukodystrophy
- disruption of oxidation of very long chain fatty acids
- accumulation of lipid in brain and adrenals
- brain damage, failure of adrenal glands, and death
- inherited X linked disorder
Describe the structure and function of mitochondria.
Can change location and shape but all have an outer and inner mitochondrial membrane with an intermembrane space and mitochondrial matrix.
Outer mitochondrial membrane: contacts cytoplasm and intermembrane space, contains pores (anion channels) that allows passage of small molecules, ions, and metabolites
Inner mitochondrial membrane: highly folded into cristae, project into matrix, contains many enzymes involved in energy production
Intermembrane space: pH and ionic composition similar to cytoplasm but contains proteins unique for ATP production, Cytochrome C lives here
Mitochondrial matrix: enclosed within inner mitochondrial membrane; contains soluble enzymes for Kreb’s, DNA transcription, etc; contains mitochondrial DNA, mitochondrial ribosomes, rRNA, mRNA, and tRNA; contains electron-dense granules that store Ca++ for regulation of ions in cytoplasm
Production of ATP through oxidation of Peru ate and fatty acids
Describe 3 differences between mitochondria and other organelles that support the hypothesis that mitochondria evolved from symbiotic prokaryotes.
- Mitochondria have own separate genome
- Mitochondria possess two membranes
- Mitochondria increase number by division
Describe how mitochondrial disease typically present.
Where are mitochondrial proteins encoded?
Mutation in what kind of DNA can result in mitochondrial myopathies? What inheritance does this show?
Proximal muscle weakness, sometimes involve extra ocular muscles. Sometimes with neuro symptoms, lactic acidosis, and cardiomyopathy
About 1/5 of oxidative phosphorylation proteins are encoded buy mitochondrial DNA, rest is nuclear genome.
Mutations in mitochondrial and nuclear genome therefore can result in mitochondrial disease. However, mitochondrial DNA is strictly maternal inheritance.
Describe the structure, function, and contents of the nucleus.
Large, membrane-limited organelle. Surrounded by double membrane called nuclear envelope.
Contains genome as DNA bound to proteins, this is known as chromatin.
Contains machinery for DNA replication, RNA transcription, and one or more nucleoli.
Describe the structure of the nuclear envelope.
1. Outer nuclear membrane: continuous with RER, ribosomes commonly attached to cytoplasmic surface
2. Perinuclear space: continuous with lumen of RER
3. Inner nuclear membrane: able to bind chromatin and lamins, supported by rigid network of intermediate filaments
4. Nuclear lamina: thin, protein-dense, attached to inner nuclear membrane, represents skeleton of nucleus formed by lamins.
Lamins: intermediate filament proteins that disassemble during mitosis and reassemble after, cross-linked into orthogonal lattice attached to inner nuclear membrane
5. Nuclear Pores: openings in envelope that allow communication between cytoplasm and nucleus, protein “spokes” project into lumen, allow free passage of small particles
Describe chromatin.
What are the two types of chromatin in a non-dividing cell?
DNA associated with nuclear proteins, like histones
- Euchromatin: transcriptionally active, loosely packed, light staining
- Heterochromatin: contains inactive DNA, densely packed, stains more intensely
