Cytology week3,4,5 Flashcards
What are lysosomes responsible for and what do they contain
- Intacellular digestion
- recycling cellular components
They contain around 40 hydrolitic enzymes that break down macromolecules
Name the 4 hyrolitiic enzymes in lysosomes
- Nucleases
- Proteases
- Phospholipases
- Phosphates
Explain the formation of lysosomes
- Lysosmal hydrolases is synthesied in the rER then transferred to the golgi apparatus where it is modified with M6P for lysosmal targetting
Explain the process in the digestion of external materials
-The membrane of the phagosome vesicle fuses with the lysosomes.
- This mixes the endocytosed materials with the lysosomal emzyme activating proton pumps in the lysosmal membrane, allowing digestion and forming a secondary lysosome(heterolysosomes)
What happens in Autophagy
-Lysosomes degrade excess or defective cells through autophagy.
-Autophagosomes form around unwanted cellular componentes and fuse with lysosomes for digestion.
What do indigestible materials form
They form residul bodies which can accumulate as lipofusion in long live cells(heart muscle and neurons)
Describe the structure and size of proteasomes and where they are found
- Large non membrane bound protein complexes
- Located in the cytoplasm and nucleus
- They consist of a cylindrical structure with 4 stacked rings
What is the difference between proteasomes and lysosomes
Proteasomes target indiviudal proteins whereas lysosomes digest organelles or membranes by autophagy
What is the role of mitochondria?
It is responsible for aerobic respiration, ATP production, providing energy for cellular activities
- They oxidise pyruvate releasing more ATP than gylcolysis
Describe the structure of mitochondria
- Elongated, highly dynamic
- Has 2 membranes, an outer sieve like membrane, and a folded inner membrane called cristae, which increases the surface area and house key enzymes for energy production
Describe the inner membrane of the mitochondria
- It contains specialised phospolipds
- It is highly impermeable to ions, hosts transport proteins
and the electron transport chain and ATP synthase for oxidative phosphorylation
What is the role of proteasomes
They degrade damaged or unecessary proteins
How is ATP produced in the mitochondria
-Electrons from the ETC create a proton gradient across the inner membrane and then protons flow back through ATP synthase, generating ATP.
What is mitochondrias role in Apoptosis?
During cell stress, mitochondria release cytochrome C, triggering apoptosis by activating cellular proteases
What is the function of peroxisomes?
- They produce and degrade hydrogen peroxide through oxidase and peroxidase
- They detoxify harmful substances, especially in the liver and kidney.
What is the role of peroxisomes in metabolism
It breaks down long fatty acid chains and synthesising bile acids and cholesterol
How are peroxsisomes formed
- By budding from the ER or by growth and divison of existing peroxisomes.
- Their proteins are synthesised in the cytosol and imported using targeting sequences
What does cytoskeleton consist of?
- Microtubules
- Micro filaments(Actin filaments)
- Intermediate filaments
What is the function of Cytoskeleton
- It provides structural supprt
- Determines the cell shape
- Enables movement of organelles and vesicles
Explain the structure of Microtubules
- Hollow rigid tubular structures
- Made of alpha and beta tubulin subunits
- Linked side by side in structures like cilia
- Highly dynamic
What is the microtubules function in intracelluler transports
- It facilitates vesicle,organelles and complex transport
What is the microtubules function in cell organization?
- They extend the ER and assist vesicle movement through Golgi apparatus
- They maintain cell shape and polarity
What is the cell cycle
Cycles of growth and division
NAME the phases of the cell cycle
- G1 Phase
-S phase
-G2 phase - Mitosis
Explain the 4 phases in the cell cycle
G1 PHASE
- Where active RNA and protein synthesis occurs, increasing cell volume
S PHASE
- DNA replication, histone synthesis and centrosome duplication happens
G2 PHASE
- Proteins required for mitosis accumulate
MITOSIS
- Cells divide, completing the cycle
What is the role of Cyclins and CDK(
-They regulate the cell cycle by activating phase specific proteins,
- Whe each phase is complete, the cyclin is removed and a new cyclin guides the cell into the next phase
What is the role of checkpoints and tummor supressor proteins
- Specific checkpoints monitor conditions and DNA integrity pausing the cycle if issues arrises
- Tumour supressor proteins such as p53 help stop the cycle for repair or tigger cell apoptosis if damages are irreperable.
Explain what happend in the G0 phase
- Differentiated cells enter the G0 phase, where the cell cycle is apsued
- Cells like liver cells can re-enter the cycle , while cells like the mucle and nerve cells stay in the G0 phase permanently.
- External signals can re-activate G0 cells
Explain the structure of the microfilaments
-Made out of actin subunits and they are
- Thin
-Flexible
-Highly dynamic
and they have polarised filaments that enable cell motility and contraction
What is Mitosis?
It is the process of cell division where a parent cell divides to produce 2 daughter cells with identical sets of chromosomes.
What is the process of prophase
- Chromosomes condense becoming visible chromosomes, each w 2 chromatids joined at the centromere .
- The Nucleolus disappears and the centromere migrate to oppiste poles forming the mitotic spindle
-The nuclear envelop disassemebels
What is the process of Metaphase
- Chromosome fully condenses and aligns at the equatorial plate
- Kinetchores on chromosomes attatch to spindle microtubules
What is the process of Anaphase
- Sister chromtids seperate and move to opposite spindle poles, now they are considered as individual chromosomes
- The spindle pores move further apart, aiding chromosome sepearation
What happens in Telopahse
-The chromosomes at the spindle poles decondense
-The nuclear envelope re assembles around each chromsom set
What are stem cells
A small population of undifferentiated cells in the tissues
What is the role of stem cells
- They enable the renewal of differentiated cells through an individuals life
Where are stem cells located
-In specifc microevironments , or niches that maintain their undifferentiate state
Where are the stem cells studied
In rapidly renewing tissues, such as blood, skin and the digestive tract
What is meiosis and what does it involve
- Cell division process that prduces halpoid gametes(sperm+egg) from diploid percursor cell
- It involves 2 cell divisions, resulting in 4 geneticically unique haploid cells
Explain the key feature of meisois:
- Synapsis + crossing over
SYNAPSIS + CROSSING OVER
- Where the homologus chromosomes pair up in a process called synapsis, allows for crossovers to occur
- The mixing of the genetic material produces new gene combinations, increasing the genetic diversity
Explain the the key feature
- Haploid cells
in meiosis
- This is the result of meiosis with half of the usual chromosome number
- This then combines during fertilisation to form a new dilpid zygote
What stages of Meiosis
- Prophase 1
- First Meiotic division
- Second Meiotic Division
What happens in the first stage of prohpase 1
-chromosome condesne , pair up , and undergo sypnapsis
- Crossing over occurs, promoting genetic variation
What happens in the first meiotic division?
- ## Homologus chromosomes seperate into new cells, each are still diploids but with paired chromatids
What happens in the third stage of meiosis
- Chromosomes seperate without DNA replication , forming halpoid cells with single chromatids each
What is the difference between Meiosis and Mitosis
Mitosis:
- Produces 2 genetically identical diploid cells
- No genetic variaton( no crossing over or recombination)
Meiosis:
Produces 4 genetically different/unique halpoid cell
Which components are in the Nucleus?
- Nuclear envelope
-Chromatin - Nucleoli
1.What is the Nuclear envelope?
2. What is the structure of the Nuclear envelope?
1- It is a selectively permeable membrane that acts as a boundary between the nucleus and cytoplasm
2- Has 2 membranes, separated by a perinuclear space
What is the inner membrane of the nuclear envelope supported by ?
- Nuclear lamina which is a protein network
What is Apoptosis
- hIghly regulated process of programmed cell division
What is the role of Apoptosis
It eliminated defective and unneeded cells without causing inflammation
What is the mechanism of Apoptosis
It is controlled by Bcl-2proteins
- The proteins regulate the release of death-promoting factors from mitochondria
- They are activated by external signals or irreversibke internal damage
Name the four basic cell types
-Epithelial tissue
-Connective tissue
- Muscle tissue
- Nervous tissue
What components do organs consist of and their function?
- Parenchyma: responsible for organs specialised fucntions
- Stroma: supports connective tissue
Name the 3 functions of the epithelial cell with a brief explanation
- Protection( supports and protects the surfaces)
- Absorption( Faciliatates nutrient uptake)
- Secretion(produces and releases substances)
What are three shapes epithelial cells can have?
Columnar
Cuboidal
Squamous
Explain the shape of the nuclei in the columnar, cuboidal or squamous cells
Elongated in columnar cells
Flattened in squamous cells
Spherical in cuboidal cells
What is the function of the basal pole and the apical pole?
Basal pole: Contracts ECM and the connective tissue
Apical pole::Faces an open space
Explain epithelial nutrient supply
-Epithelial lack blood vesselsand depend on on nutrients and oxygen from adjacent connective tissues
What is Laminate propria.
Connective tissues underlying the epithelia
What is the function of the basment membrane in the Epthelial cells
- Provides structural support
- Maintains epithelial polarity
- Facilitates epithelial repair
- Regulates molecular filtration
What is the basment membrane
- A thin extracellular sheet supporting the epithelial cells
- Acts as a semipermeable filter for substances
How does the basment membrane look in the TEM
- It is visible under 2 layers.
- basal lamina
- Reticular Lamina
Explain tight (occluding) junctions
+ what they contain
- Located at the apical end forming a seal between cells to prevent the flow of materials between epithelial cells.
-Prevent paracellular transport
composed of claudin and occluding proteins
What are the functions of the tight junctions
- Prevent paracellular transport
- Form a seal between cells to prevent the flow of materials between epithelial cells
What are Zonula Adheren junctions
+ what are they mediated by
-Encircle cells below tight junctions
- Cadherins
What is the function of Adherene junctions
-Provides mechanical strength and links to a cytoskeleton network
What is the function of desmosomes junctions
What are desmosomes composed of
Provide firm adhesion and resilience against mechanical stress
-Desmoglein, desmocollins, desmoplakins
What do gap junctions consisit of
- ## Aggregated transmembrane protein complexes that form circular patches in the plasma membrane
What is the structure and function of microvilli?
- Small uniform cytoplasmic projections
Covered by glycoalyx containing enzymes for digestion
What does microvilli contain(components)
Contains bounded actin filaments , stabilised by actin-binding proteins
What is the structure of stereocilia?
- It is longer and less motile than microvilli
Where are stereocilia found?
- In male reproductive systems and the inner ear
What are the components of stereocilia?
Have actin filaments connected to the terminal web
What is the function of the cilia( motile and non motile)
Motile:Generates fluid movement along the epithelial surface
Non motile: detect environmental signals
Where is the flagella found?
- Found in sperm cells
What is the function of the flagella
Enables movement
What dose chromatin consist of
- DNA and associated proteins
What is the function of Nuclear pores?
Facilitate the movement of ion, molecules and macromolecules
Name the types of Chromatin
- Eurochromatin
-Heterochromatin
Explain heterochromatin
- Dense, transcriptinally inactive includes:
- Constitutive heterochromatin
- Facultative heterochromatin
Explain eurochromatin
- Lightly stained , transcriptionally active
Cells with more eurochromatin are ……
Metabolically active
Cells with more hetero eurochromatin are……..
Less active
what is it called when the basement membrane of the epithelial cell has one cell layer and describe the cells shape
Simple
cells off simple epithelia are either squamos, cuboidal, or columnar
What is epithelia called with 2 or more layers of cells and the shape
- Stratified
Mostly all of the stratified epithelia are stratified squamos
What is the function of the stratified squamos epithelia
- Move from the basal to the surface layers
- become filled with keratin intermediate filaments
Name an exmaple of stratified squamos epithelia and its function
- Epidermis
- Covers the body surfaces
- protects the underlying tissues from excess water loss
What is the functions of Macrophages?
-Specialize in phagocytosis
-Secrete growth factors critical for tissue repair and regeneration
-Play a role in antigen processing and presentation for lymphocyte activation.
-Abundant at sites of inflammation and involved in tissue repair.
What are the characteristics of Macrophages: Nucleus, surface and Cellular structure
Nucleus:
- Oval or kidney shaped
Surface:
- Irregular with pleats and protrusions, aiding pinocytotic and phagocytic activity
Cellular Structure:
- Contains well developed Golgi Apparatus and
many lysosomes
Where do Macrophages orgiinate from?
-
Where do Monocytes form?
-Monocytes form in the yolk sac during early embryonic development and become part of the mononuclear phagocyte system
Name the gap junction proteins
Connexins
What is the function of Gap junctions
- Permit intracellular exchange of molecules with small dimateres
What does hemidesmosomes contain
Integrins
What causes blistering
- Abnormal desmosome function
What causes food poisoning
- The secretion of the enterotoxin by clostridium perfringes , which binds to claudin molecules of the intestinal cells
What is the name of the bacteria involved in gastric ulcers
Helicobacter pylori
Explain how helicobacter pylori causes gastric ulcers
Binds to extracellular domains of tight junctions , inserting a protein ino the cells which target ZO-1 and distrupts the signalling
Where are microvilli found
- Found in small intestine and retinal proximal tubular cells
How does the bc1 proteins carry out their function during apoptosis
- Rlease cytochrome c into the cytoplasm
-Where it attahes to the Proteolytic enzymes called caspases - Intial caspases activate a cascade of other caspases , resulting in a protein degeneration throughout the cell
What is the outer membrane of the nuclear envelope continous with
Rough endoplasmic reticulum
What is the inner membrane of the nuclear envelope supported by
- Nuclear lamina
Where is constitutive heterochromatin found and what does it contains
-Found in all cells
- Contain repetitive sequences
What can facultative heterochromatin switch between
- Active and inactive states
What do Nucleoporins regulate transport of
Ribosomal subunits, RNA and transcriptional factors
