cells - fred sheeny
Cell Structure & Function
1. Cytoplasm
Consists of cytosol and membrane-bound organelles.
Area defined by nuclear membrane and plasma membrane.
Cytosol: Transparent intracellular fluid containing ions, biomolecules, and proteins.
Concentration gradient facilitates metabolism.
2. Protein Complexes
Inflammasomes, Apoptosomes, Centrosomes enable cell signaling/division.
3. Cytoskeleton
Provides shape, structure, and motility.
Actin Filaments: Cell growth, Myosin-mediated movement.
Intermediate Filaments: Cell-specific proteins, organize 3-D shape.
Microtubules: Tubulin polymers, aid in cellular organization.
4. Endomembrane System
Nuclear envelope, endoplasmic reticulum, Golgi apparatus, lysosomes, vacuoles, plasma membrane.
Continuous or connected via vesicles.
Dynamic role in compartmental organization.
Endoplasmic Reticulum
Network from nucleus into the cell.
Rough ER: Ribosomes for protein synthesis/modification.
Smooth ER: No ribosomes, involved in lipid synthesis/detoxification.
Vesicles transport materials.
Golgi Apparatus
Membrane network sorting cellular traffic.
Cis face (receiving side), trans face (shipping side).
Traffics lipids/proteins to/from ER.
Produces new membrane-bound organelles/vesicles.
Vesicle Destination from Golgi
Endo-Lysosome: For recycling.
Plasma Membrane: Transport functions.
mcq :
1. What comprises the cytoplasm?
a) Only cytosol
b) Membrane-bound organelles
c) Cytosol and membrane-bound organelles
d) Nucleus and plasma membrane
2. Which protein complexes are involved in cell signaling and division?
a) Endosomes and lysosomes
b) Golgi apparatus and centrosomes
c) Inflammasomes and apoptosomes
d) Mitochondria and ribosomes
3. What is the primary function of actin filaments?
a) Energy production
b) Cellular growth
c) Lipid synthesis
d) Protein degradation
4. Which component organizes the 3-D shape of cells?
a) Actin filaments
b) Intermediate filaments
c) Microtubules
d) Golgi apparatus
5. Which organelle is responsible for lipid synthesis and detoxification?
a) Rough endoplasmic reticulum
b) Smooth endoplasmic reticulum
c) Golgi apparatus
d) Lysosomes
6. What is the function of the cis face of the Golgi apparatus?
a) Receiving side
b) Shipping side
c) Protein synthesis
d) Lipid modification
7. Where does the trans face of the Golgi apparatus transport materials?
a) Endo-lysosome
b) Mitochondria
c) Nucleus
d) Plasma membrane
8. What is the role of vesicles in the endomembrane system?
a) Energy production
b) Detoxification
c) Transport materials
d) Cell division
9. Which cellular structures are composed of tubulin polymers?
a) Actin filaments
b) Intermediate filaments
c) Microtubules
d) Endosomes
10. Which organelle is involved in recycling within the cell?
a) Endoplasmic reticulum
b) Golgi apparatus
c) Endo-lysosome
d) Plasma membrane
Golgi Apparatus Functions:
Traffic Director: Receives and sorts molecules, directing them to specific destinations within or outside the cell.
Post-Translational Modification: Alters proteins' chemical structures via processes like phosphorylation, sulfation, and glycosylation, affecting their properties and roles within the cell.
Protein Handling in a Cell:
Protein Synthesis: Amino acid chains assembled through translation.
Post-Translational Modification: Chemical alterations, such as glycosylation or phosphorylation, affecting protein function.
Delivery to Golgi: Proteins with modifications transported to the Golgi apparatus.
Sorting and Packaging in Golgi: Further processing and sorting of modified proteins for targeted cellular destinations.
Endocytosis:
Phagocytosis: Engulfs larger particles like food or pathogens.
Pinocytosis: Absorbs dissolved substances from the surroundings.
Receptor-Mediated Endocytosis: Specific uptake facilitated by receptors on the cell's surface, allowing only substances that match the receptors to be brought inside the cell.
Intracellular Processing: Materials enclosed in vesicles are processed within the cell to support various cellular functions like energy production or structural maintenance.
Golgi Apparatus:
What is the primary function of the Golgi apparatus in a cell?
a) Energy production
b) Protein synthesis
c) Sorting and directing molecules
d) Cell division
Which process occurs in the Golgi apparatus to modify proteins after their synthesis?
a) Glycolysis
b) Phagocytosis
c) Post-translational modification
d) Transcription
What chemical alterations can the Golgi apparatus perform on proteins?
a) Dehydration
b) Glycosylation
c) Anaerobic modification
d) Nucleotide attachment
Protein Handling in a Cell:
Where do proteins undergo post-translational modifications in the cell?
a) Endoplasmic reticulum
b) Nucleus
c) Golgi apparatus
d) Lysosomes
Which step follows protein synthesis in the sequence of protein handling in a cell?
a) Post-translational modification
b) Protein degradation
c) Vesicle formation
d) mRNA transcription
What cellular organelle receives proteins for modification after their synthesis?
a) Lysosomes
b) Nucleus
c) Golgi apparatus
d) Endoplasmic reticulum
Endocytosis:
Which type of endocytosis involves the cell engulfing larger particles?
a) Receptor-mediated endocytosis
b) Pinocytosis
c) Phagocytosis
d) Exocytosis
What is the primary function of pinocytosis?
a) Engulfing larger particles
b) Absorbing dissolved substances
c) Targeting specific substances with receptors
d) Exporting materials out of the cell
Which endocytosis process involves specific receptors on the cell's surface?
a) Phagocytosis
b) Pinocytosis
c) Exocytosis
d) Receptor-mediated endocytosis
Cellular Processes:
What cellular function is primarily associated with the Golgi apparatus?
a) DNA replication
b) Protein modification and sorting
c) Cellular respiration
d) Cell membrane synthesis
Which cellular process involves modifying proteins after their synthesis?
a) Transcription
b) Translation
c) Post-translational modification
d) RNA splicing
Which cellular structure is responsible for directing and sorting various substances inside the cell?
a) Lysosomes
b) Golgi apparatus
c) Endoplasmic reticulum
d) Mitochondria
Lysosomes:
Specialized organelles containing enzymes for breaking down waste materials, old cell parts, or foreign substances.
Utilize acidic environments and hydrolytic enzymes to digest and recycle cellular waste.
Synthesis of degradative enzymes occurs in the endoplasmic reticulum (ER), then processed and packed in the Golgi apparatus before reaching lysosomes.
Plasma Membrane (Cell Membrane):
Acts as a protective barrier around the cell, separating internal environment from the external surroundings.
Structure:
Composed of phospholipid bilayer with hydrophilic heads and hydrophobic tails.
Contains proteins integral for transport, signaling, and structural support.
Adheres to the fluid mosaic model due to the fluid nature of the lipid bilayer with proteins interspersed.
Functions:
Selective permeability, allowing specific substances to pass.
Facilitates cell signaling and communication.
Aids in transport of molecules in and out of the cell.
Contributes to cell adhesion, allowing cells to form tissues and organs.
Fluidity:
Lipid bilayer's flexibility (amphipathic nature of lipids) crucial for cell activities and movements.
Amphipathic Nature of Lipids:
Lipids possess hydrophilic and hydrophobic portions, making them amphipathic.
Phospholipids have hydrophilic heads and hydrophobic tails, forming structures like micelles or phospholipid bilayers.
Phospholipid bilayers tend to form circular shapes, providing the cell's structural integrity.
Lysosomes:
Where are degradative enzymes for lysosomes primarily synthesized and processed before reaching the lysosomal compartment?
a) Golgi apparatus
b) Endoplasmic reticulum
c) Nucleus
d) Mitochondria
What is the primary function of lysosomes within a cell?
a) Protein synthesis
b) Energy production
c) Digestion and recycling of cellular waste
d) Cell division regulation
Plasma Membrane:
Which model describes the structure of the plasma membrane as a fluid structure with proteins interspersed?
a) Phospholipid model
b) Mosaic model
c) Hydrophilic model
d) Lipid bilayer model
What property of the plasma membrane allows for the selective passage of substances in and out of the cell?
a) Hydrophilicity
b) Amphipathy
c) Selective permeability
d) Hydrophobicity
Amphipathic Nature of Lipids:
What term describes the arrangement of phospholipids in a circular formation due to their amphipathic properties?
a) Micelle structure
b) Bilayer formation
c) Hydrophilic association
d) Lipid aggregation
Which portion of the phospholipid tends to interact with the external aqueous environment surrounding the cell due to its hydrophilic nature?
a) Hydrophobic tail
b) Hydrophilic head
c) Amphipathic region
d) Lipid core
Transport across the plasma membrane
Water (Polar) passes through osmosis (osmotic pressure)
Polar molecules (Ions/Simple nutrients) can diffuse through
- not easily cross the bi-layer because of the hydrophobic centre
- Concentration Gradients allow this (Push-Pull Effect)
Hydrophobic non-polar molecules pass through via diffusion more easily
Protein Transporters assist the process:
- Ion Channels/Transporters – permit entry
- Receptors – detect substances and initiate cellular responses
- Some proteins facilitate passive diffusion through Carrier
- Some requires energy/stimulation
Cellular Transport System facilitates transport
Production of Vesicles from Golgi to transport proteins out (Secretion & Exocytosis)
Substances can enter via Endocytosis (Pinocytosis - nutrients)
Bacterial Cell Wall:
Provides additional support to bacterial cells.
Composed of lipid, lipoprotein, and carbohydrate/sugar species.
Some bacteria have an outer "plasma membrane" outside their cell wall, providing specificity/selectivity.
Components of the cell wall and membrane associated with immunogenicity, pathogenicity, and targeted by antibiotics.
Structures like flagella and pillae aid in movement or substrate attachment.
Certain bacteria possess a polysaccharide capsule outside the cell wall or develop tougher structures like spores for survival.
Bacterial Kingdom Division:
Divided into Gram-positive and Gram-negative based on cell wall structure and staining behavior under biochemical assays (Gram stain).
Gram-Positive Bacteria:
Lack outer membrane.
Majorly composed of peptidoglycan cell wall.
Stain positive and retain counterstain.
Smaller periplasmic space.
Gram-Negative Bacteria:
Contain outer membrane with numerous lipids/lipoproteins and transport proteins.
Thin peptidoglycan cell wall.
Stain negative.
Possess a periplasmic space.
Plant Cell Walls:
Neighboring cell walls exist side by side.
Each wall comprises three layers:
Plasma membrane (innermost).
Three layers of cellulose forming the "primary wall."
Outer "middle lamella," creating division/border with neighboring cells.
Eukaryotic Cell Separation:
The earliest step in eukaryotic cell separation involved the formation of the endoplasmic reticulum, the establishment of the defined nucleus, and the development of the nuclear membrane.
Levels of Replication:
DNA Replication:
Involves unwinding and copying the entire genome, creating duplicate chromosomes.
Vital for cellular growth, expansion, and division.
The double-helix structure enables DNA replication and transcription for protein synthesis.
DNA Transcription:
Regulated unwinding of specific genome sections to form an RNA copy.
DNA, along with histone proteins, forms nucleosomes, which constitute chromatin and eventually chromosomes.
The centromere serves as an anchor for chromatids.
Types of Cellular Division:
Binary Fission:
Occurs in bacteria; involves division into two identical daughter cells.
Budding:
Observed in yeast and diatoms, leading to the formation of new cells from parent cells.
Mitosis (Used in Most Eukaryotic Cells):
Includes DNA replication, chromosome duplication, and separation.
Involves cytokinesis, the process of separating chromosomes and dividing the cytoplasm.
Cytokinesis Process:
Formation of Cleavage Furrow (Animal Cells) or Cell Plate (Plant Cells):
Animal cells develop a cleavage furrow, while plant cells form a cell plate.
Constriction or Formation of New Cell Wall:
In animal cells, actin filaments create a contractile ring, leading to cell pinching and division.
Plant cells utilize Golgi vesicles to construct a new cell wall that divides the cell.
Completion of Separation:
Animal cell cleavage furrow deepens to separate the daughter cells.
Plant cell's cell plate continues forming, ultimately separating the daughter cells.
Formation of Identical Daughter Cells:
After cytokinesis, two genetically identical daughter cells form, each containing its own nucleus and organelles.
Mitotic Spindle Components:
Microtubule Proteins: Long, slender filaments radiating from centrosomes, attaching to chromosomes and aiding their movement during mitosis.
Centrosome Complex: Contains centrioles organizing microtubules, ensuring proper spindle formation for chromosome segregation.
Polarity Establishment: Establishes two distinct poles, guiding chromosome segregation for equal distribution.
Centrosome and Microtubule Organization:
MTOC (Microtubule Organizing Center): Where centrosomes, composed of centrioles, coordinate microtubule organization.
Centrioles: Made of tubulin proteins forming hollow tubes, part of the centrosome's structure.
Pericentriolar Material: Surrounds centrioles, aiding in microtubule organization.
Singular Centrosome: Usually one per cell, positioned close to the nucleus.
Centrosome Cycle:
Centriole Structure: Two sets of centriole subunits oriented perpendicular to each other.
Duplication and Separation: Duplication before cell division, ensuring each daughter cell receives a centrosome.
Centriole Movement: Separation of linked subunits forming distinct centrioles that migrate to opposite cell poles.
Spindle Formation and Mitotic Separation:
Microtubule Origin: Microtubules extend from centrosomes into the cytoplasm.
Tubulin Addition: Addition of tubulin subunits expands microtubules, forming asters and spindle microtubules.
Kinetochore Proteins: Specific proteins on chromosomal centromeres targeted by spindle microtubules to aid accurate chromosome separation.
Mitosis Chromatid Separation:
Separase Enzyme: Assists in breaking connections between sister chromatids.
Chromatid Movement: Separated chromatids migrate apart along kinetochore microtubules.
Kinetochore Microtubules: Attach to kinetochores on chromatids, shorten through depolymerization, aiding in chromatid movement to opposite cell ends.
Cytokinesis: Division of Cytoplasm
Establishment of Polarity:
Opposing centrosomes create polarity, guiding the division process.
Aster Microtubules' Role:
Short aster microtubules exert opposing forces, pushing away from the cell center.
Non-Kinetochore Microtubules:
Elongate the cytoplasm in opposite directions before cell separation.
Cytokinesis - Cleavage:
Formation of Cleavage Furrow:
Contractile ring of microfilaments creates a cleavage furrow post-chromosomal separation.
Microfilament Bundles Post-Chromosomal Separation:
Actin and myosin proteins form microfilament bundles at the cell's center.
Counteracting Spindle Forces:
Microfilament bundles counteract spindle apparatus forces, preventing excessive elongation.
Cleavage Membrane Invagination:
Microfilament bundles aid in inward folding of the cell membrane, forming the cleavage furrow.
Pinching Into Daughter Cells:
The cleavage furrow deepens, gradually pinching the cell into two distinct daughter cells during cytokinesis.
What is the primary function of DNA replication in cellular processes?
a) Synthesizing nucleosomes
b) Aiding in cellular division
c) Forming nucleotides
d) Creating chromatin structures
Which cellular division type involves the division into two identical daughter cells and is predominantly observed in bacteria?
a) Mitosis
b) Binary Fission
c) Budding
d) Meiosis
What is the role of microtubule proteins in mitotic spindle components during mitosis?
a) Formation of cleavage furrow
b) Attaching to centrioles
c) Pushing away from cell center
d) Aiding in chromosome movement
What is the function of kinetochore proteins during mitosis chromatid separation?
a) Assisting in breaking chromatid connections
b) Attaching to centrosomes
c) Shortening microtubules
d) Elongating the cytoplasm
Which process involves the formation of a cleavage furrow or cell plate post-chromosomal separation?
a) DNA replication
b) Centriole duplication
c) Cytokinesis
d) Kinetochore attachment
What is the significance of non-kinetochore microtubules in cytokinesis?
a) Counteracting spindle forces
b) Forming centrosomes
c) Elongating the cytoplasm
d) Initiating chromosome separation
During cytokinesis in animal cells, what structure forms a contractile ring aiding in cell pinching and division?
a) Actin and myosin bundles
b) Tubulin subunits
c) Kinetochore microtubules
d) Pericentriolar material
Which step during cytokinesis involves inward folding of the cell membrane, forming the cleavage furrow?
a) Formation of aster microtubules
b) Elongation of non-kinetochore microtubules
c) Actin and myosin bundle formation
d) Cleavage membrane invagination
What establishes polarity in cytokinesis by exerting forces in opposite directions?
a) Centrosome duplication
b) Formation of cleavage furrow
c) Non-kinetochore microtubules
d) Aster microtubules
Which event aids in the gradual pinching of the cell into two distinct daughter cells during cytokinesis?
a) Cleavage membrane invagination
b) Formation of non-kinetochore microtubules
c) Counteracting spindle forces
d) Formation of contractile ring
What is the primary role of the centrosome in cellular division?
a) Formation of nucleosomes
b) Organization of microtubules
c) Regulation of DNA replication
d) Synthesis of chromatids
Which type of cellular division involves the elongation of the cytoplasm in opposite directions before cell separation?
a) DNA Replication
b) Cytokinesis
c) Kinetochore attachment
d) Centriole duplication
What function does the cleavage furrow serve during cytokinesis?
a) Formation of contractile ring
b) Separation of chromatids
c) Formation of cell plate
d) Gradual pinching of the cell
During mitosis chromatid separation, what is the role of kinetochore microtubules?
a) Attachment to centrioles
b) Shortening of microtubules
c) Movement of chromatids
d) Formation of asters
What is the significance of the pericentriolar material in the centrosome?
a) Formation of spindle microtubules
b) Regulation of DNA transcription
c) Formation of contractile ring
d) Organization of centrioles
Which cellular component forms a contractile ring of microfilaments in animal cells during cytokinesis?
a) Actin and myosin bundles
b) Kinetochore microtubules
c) Centrioles
d) Pericentriolar material
What is the primary function of aster microtubules during cytokinesis?
a) Counteracting spindle forces
b) Formation of contractile ring
c) Establishing cell polarity
d) Shortening of microtubules
Which cellular process involves the duplication and separation of centrioles before cell division?
a) Cytokinesis
b) DNA Transcription
c) Centrosome cycle
d) Mitosis
What structure forms in plant cells to separate daughter cells during cytokinesis?
a) Contractile ring
b) Cleavage furrow
c) Cell plate
d) Aster microtubules
Which step in cytokinesis involves the inward folding of the cell membrane?
a) Formation of cleavage furrow
b) Elongation of non-kinetochore microtubules
c) Counteracting spindle forces
d) Cleavage membrane invagination
The cell cycle
The interpahse is further divided into
G1
S
G2
There are further stages of the mitosis phase of the cell cycle
-Prophase
- Pro-Metaphase
- Metaphase
- Anaphase
- Telophase
The cell cycle checkpoints
Availability of Metabolites: Checkpoints in the cell cycle ensure that the cell has enough essential resources (metabolites) required for the division process.
Signals from External and Internal Environment: The cell cycle progression is also regulated by signals from both the external environment (like growth factors) and internal cellular conditions.
Control to Prevent Excessive Proliferation: Checkpoints are important to prevent excessive cell division, as uncontrolled or excessive proliferation can lead to the development of cancer.
Apoptosis - Programmed Cell Death: Sometimes, cells need to undergo programmed cell death, known as apoptosis. This process helps eliminate unwanted or damaged cells, maintaining the overall health and functionality of the organism by ensuring the removal of abnormal cells.
There is also a checkpoint after g2 and another after the anaphase of mitosis
Functions of cell division
Propagation
Growth & embryonic development
Repairs & Renewal
Sexual reproduction
In meoisis the fidelity of the genetic material is not totally preserved allowing for the evolution to occur