cell concept summary Quiz

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Questions and Answers

What is the primary role of microtubules in the cytoskeleton?

Facilitating transport and maintaining cell shape (correct)

Allowing muscle contraction and movement

Providing mechanical strength to the cell

Serving as a flexible lattice beneath the plasma membrane

Which cytoskeletal component is primarily involved in muscle contraction?

Actin filaments (correct)

Microtubules

Cytosol

Intermediate filaments

How do intermediate filaments contribute to cellular structure?

They anchor organelles in place

They assist in the movement of vesicles

They form polymers that facilitate transport

They provide structural support and mechanical strength (correct)

Which statement about the cytoskeleton is incorrect?

Microtubules assist in cell movement Signup and view all the answers

What is the role of spectrin in red blood cells?

Forming a flexible lattice beneath the plasma membrane Signup and view all the answers

Which of the following functions is NOT performed by the cytoskeleton?

Providing a barrier against pathogens Signup and view all the answers

Which structure is involved in stabilizing the shape of red blood cells?

Spectrin Signup and view all the answers

What key attribute do all components of the cytoskeleton share?

They are all polymers made from monomeric units Signup and view all the answers

What is the main function of telomerase in relation to chromosomes?

It extends the telomeres by adding repeating units. Signup and view all the answers

During which phase of the cell cycle does DNA replication occur?

S Phase Signup and view all the answers

Which event occurs during prophase of mitosis?

The nuclear envelope begins to disintegrate. Signup and view all the answers

What role do astral microtubules play in the spindle apparatus?

They anchor the spindle to the cell cortex. Signup and view all the answers

What characterizes the G2 phase of the cell cycle?

The cell prepares for mitosis by synthesizing proteins. Signup and view all the answers

Which component of the spindle apparatus is involved in focusing the spindle poles?

Dynein Signup and view all the answers

How are chromosomes positioned during metaphase?

They align at the metaphase plate. Signup and view all the answers

Which type of microtubule attaches to the centromere at the kinetochore?

Kinetochore microtubules Signup and view all the answers

What role do satellite cells play in muscle tissue?

They are involved in the proliferation and repair of damaged muscle fibers. Signup and view all the answers

Which characteristic of satellite cells differentiates them from other stem cells?

They divide in response to injury or growth signals only. Signup and view all the answers

Which of the following statements is true regarding the pancreas and liver?

Differentiated cells in these organs can divide to replace lost cells. Signup and view all the answers

What is a limitation of sensory epithelial tissues, such as in the adult mammalian ear and eye?

Once sensory cells are lost, they cannot be replaced. Signup and view all the answers

Which type of cells amplify cell division before differentiating?

Progenitor cells Signup and view all the answers

What effect does Taxol (Paclitaxel) have on microtubules?

It stabilizes microtubules and arrests cell division. Signup and view all the answers

Which structure is considered the core support for cilia and flagella?

Axoneme Signup and view all the answers

What is the function of the outer microtubule doublets in cilia and flagella?

They provide structural framework. Signup and view all the answers

In the context of undulipodia, what arrangement of microtubules is characteristic?

9(2) + 2 arrangement Signup and view all the answers

What role do dynein arms have in ciliary motion?

They generate the force required for movement. Signup and view all the answers

What distinguishes cilia from flagella in terms of their movement?

Cilia beat in a coordinated fashion, while flagella beat independently. Signup and view all the answers

Which feature defines euchromatin?

Uncondensed and genetically active. Signup and view all the answers

What is the primary function of ciliated epithelial cells in the respiratory system?

Clearing harmful materials from airways. Signup and view all the answers

What is the primary role of interpolar microtubules during mitosis?

They maintain spindle structure by overlapping between poles. Signup and view all the answers

Which motor protein is primarily responsible for focusing the spindle poles?

Kinesin Signup and view all the answers

What is the function of the kinetochore during mitosis?

To link chromosomes to the spindle microtubules. Signup and view all the answers

Which process is initiated by the cleavage of cohesin during anaphase?

Separation of sister chromatids. Signup and view all the answers

What role does condensin play during mitosis?

It facilitates chromosome folding and condensation. Signup and view all the answers

What does dynein primarily contribute to in the context of the spindle?

Regulating spindle length and positioning. Signup and view all the answers

Which statement accurately describes the relationship between kinetochore and centromere?

The kinetochore is a protein complex assembled at the centromere. Signup and view all the answers

How does tension at the centromeres get generated during metaphase?

By the bipolar attachment of kinetochores to microtubules. Signup and view all the answers

What is the primary purpose of 5' capping of mRNA?

To enhance mRNA stability Signup and view all the answers

Which of the following correctly describes alternative splicing?

It allows a single gene to produce different mRNA isoforms. Signup and view all the answers

What role do nuclear export receptors play in mRNA transport?

Recognize the mRNA-protein complex for export Signup and view all the answers

In the context of DNA, which nitrogenous bases are paired according to the Watson-Crick model?

Adenine - Thymine, Cytosine - Guanine Signup and view all the answers

Which of the following is NOT a component of a DNA nucleotide?

Ribose sugar Signup and view all the answers

Which process occurs after mRNA is exported to the cytoplasm?

Translation into protein by ribosomes Signup and view all the answers

What is the function of the poly-A tail added to mRNA?

Protecting mRNA from degradation Signup and view all the answers

How do DNA strands orient in relation to each other?

They run in opposite directions (antiparallel). Signup and view all the answers

Study Notes

Cell Biology - Final Exam Summary

Cells are compartmentalized by membranes creating distinct environments
Cytosol (intracellular fluid) can contain organized regions contributing to function
The cytoskeleton maintains cell shape, acts as a track for organelles, anchors organelles, and facilitates movement
Microtubules (tubulin proteins) maintain shape, organize structures, and facilitate transport
Intermediate filaments provide structural support and strength
Actin filaments (ATP-actin monomers) are involved in movement, shape changes, and muscle contraction
Cytoskeletal components are polymers, long chains of monomeric units
Electron Microscopy (EM) studies reveal three key components microtubules, microfilaments (actin), and intermediate filaments
Cytoskeleton functions include maintaining cell shape, providing tracks for organelle and vesicle movement, anchoring organelles, and facilitating organelle and vesicle transport
Red blood cells (RBCs) use the cytoskeleton to maintain shape and flexibility
Microtubules, spectrin, ankyrin, and actin filaments are key components
Actin-associated proteins (like tropomyosin and protein 4.1) regulate interactions and contribute to RBC stability
Polarized epithelial cells have a cytoskeleton with a specific structure (especially in microvilli) to maintain polarity, and function (especially in microvilli). Actin filaments stabilize microvilli in polarized cells. Microtubules aid in intracellular transport and organelle positioning, while intermediate filaments (keratins) provide mechanical strength and cell anchoring.

Topic 2: Microtubules and Transport

Microtubules act as intracellular highways for protein and organelle transport, with motor proteins guiding movement along microtubule tracks
Kinesin moves cargo towards the positive (+) end (typically towards the plasma membrane and ER)
Dynein moves cargo towards the negative (-) end (typically toward the Golgi complex or nucleus)
Microtubules have intrinsic polarity; the positive (+) end directs outward transport and the negative (-) end directs inward transport
Organelles and vesicles rely on the microtubule network for positioning and movement
Cytoskeleton components (myosin, kinesin, and dynein) are involved in muscle contraction, vesicle transport, cell division, and migration. Kinesin (microtubules) moves towards the plus (+) end, involved in anterograde transport (to the cell periphery) and organelle positioning. Dynein (microtubules) moves towards the minus (-) end, involved in retrograde transport (to the cell center), cilia/flagella movement, and endocytosis.
Duchenne Muscular Dystrophy is an X-linked recessive genetic disorder affecting primarily males, characterized by progressive muscle degeneration.

Topic 3: Desmosomes and Cell Junctions

Desmosomes are cell-to-cell junctions providing mechanical strength to tissues under stress, using intermediate filaments (keratins) as their cytoskeleton component.
Hemidesmosomes anchor cells to the basement membrane, also using intermediate filaments (keratins) as their cytoskeletal component.
Focal adhesions (actin-based) and hemidesmosomes (intermediate filament-based) connect cells to the extracellular matrix (ECM) enabling cell signaling and migration

Topic 4: Microtubule Characteristics and Function

Microtubules are composed of tubulin monomers (α and β), forming hollow structures
Alpha tubulin binds GTP tightly, but doesn't hydrolyze it
Beta tubulin binds GTP and hydrolyzes it, regulating dynamics
The basic building block (tubulin dimer) is formed by combining α and β tubulin
In cells, microtubules serve as tracks for intracellular transport of vesicles, with kinesin moving toward positive end and dynein to the negative end
Microtubules form the spindle apparatus (for cell division) and core of cilia and flagella

Topic 5: Microtubule-Specific Drugs

Colchicine prevents tubulin polymerisation and inhibits mitosis (cell division)
Vinblastine/Vincristine inhibits microtubule assembly and arrests cell cycle
Taxol stabilises microtubules, inhibiting disassembly and arrests cell division
Microtubules are integral components in cilia and flagella structures forming the axoneme, which is the core microtubule framework. Outer microtubules surround the axoneme providing structural support

Topic 6: Nuclear Structure and Function

The nucleus is 25% protein and RNA combined with proteins forming rRNA
The fibrous lamina is a network of filaments near the inner nuclear membrane (and associated proteins) which provides mechanical support, regulates DNA replication, and cell division
The nucleoplasm is a gel-like substance in the nucleus that stores chromatin (DNA plus proteins)
The nuclear envelope is broken down during prophase, then reformed in the telophase
The nuclear lamina is a meshwork of filaments near the inner nuclear membrane. Lamins, a class of intermediate filaments, compose the lamina. Phosphorylation of lamins breaks down the lamina during prophase, while dephosphorylation reforms it (during telophase)
Nucleosomes are basic units of chromatin, consisting of a histone octamer (8 histone proteins) around which DNA is wrapped. The N-terminal histone tails (the "tails" of histones) are highly mobile and change conformation based on bound proteins
Histones are positively charged proteins that interact with negatively charged DNA (in the nucleosomes). Acetylation reduces the positive charge of lysine residues (activating gene expression), Methylation occurs on lysine and arginine (generally inhibiting gene expression), and Phosphorylation adds a negative charge to serine residues (influencing gene expression). Methylation and deacetylation silence genes by making the DNA less accessible to transcription machinery

Topic 7: Nuclear Import and Export

A nuclear localization signal (NLS) is a specific amino acid sequence that serves as a signal for nuclear import
Importins and exportins are proteins that mediate import/export across the nuclear pore complex. Importins bind to the cargos NLS, causing the cargo to move into the nucleus via the nuclear pore complex. Exportins are involved in nuclear export.
Hydrolysis of GTP is critical in modulating importins/exportins activities.
Ribosomes are made in the nucleus but need to be exported.
DNA replication is the process where the DNA is copied. DNA unwinds to create two complementary strands.
The new strands are built as complementary copies of the original strand through base-pairing. The mechanism of DNA replication is semi-conservative: each new strand contains one original strand and one entirely new strand.
mRNA undergoes further processing after export, including removal of CBC proteins and the addition of other factors (e.g. initiation factors) to prepare for translation into protein.

Topic 8: DNA Replication and Transcription

DNA polymerase synthesizes new DNA strands by adding nucleotides. DNA helicase unwinds DNA strands. DNA primase synthesizes short RNA primers. Single-strand binding proteins keep DNA strands separated. The leading strand is synthesized continuously in the 5′ to 3′ direction. The lagging strand is synthesized in fragments called Okazaki fragments in the 3′ to 5′ direction (due to the anti-parallel nature of DNA strands). DNA ligase seals Okazaki fragments to form a continuous strand.
Gene: a DNA sequence that encodes a protein
Transcription is the process where a gene is copied into an mRNA (messenger RNA). RNA polymerase synthesizes mRNA from the DNA template
RNA polymerase II is the type of polymerase that synthesizes mRNA in eukaryotes, and mRNA is a copy of a gene
Transcription in eukaryotes is regulated by a complex network. Transcription factors, mediators, and chromatin remodeling complexes ensure DNA is accessible

Topic 9: Eukaryotic mRNA Processing

Exons are the coding regions of a gene, and introns are the non-coding regions
Splicing is the process in the nucleus that removes introns from the pre-mRNA and joins exons together forming mature mRNA
Alternative splicing produces different mRNA isoforms from the same gene
Mature mRNA molecules are modified by 5' capping and polyadenylation at the 3' end, which enhances stability and promotes translation initiation. This helps in regulation.

Topic 10: DNA Packaging

DNA is packaged in chromatin, containing DNA and proteins (primarily histones). Nucleosomes form the basic unit of chromatin that forms a chain—like structure. Chromatin fibers are folded into loops and further condense during cell division, to form a visible chromosome
Chromosomes are thread-like structures in cells. They help DNA fit in the nucleus whilst allowing access for processes like replication and gene regulation.

Topic 11: Chromatin Structure and Modification

Euchromatin is loosely packed, actively transcribed; Heterochromatin is tightly packed, transcriptionally inactive.
Histone proteins are positively charged to bind tightly to negatively charged DNA
Histones are subject to various covalent modifications (acetylation, methylation, phosphorylation) at their N-terminal tails; modifications are cell cycle-dependent. These modifications affect gene expression

Topic 12: Chromatin Maintenance and Chromosome Structure

Structural Maintenance of Chromosomes (SMC) proteins (e.g., cohesins and condensins) are critical for maintaining chromosome structure, especially during metaphase (by holding sister chromatids). Cohesins act as intra-cross-linkers holding chromatids together, preventing separation before proper alignment, whereas condensins assist in tightly coiling (intra-cross-linkers) of chromosomes for compaction and proper organization
The centromere is a region of the chromosome where sister chromatids are most tightly bound, essential for attaching the chromosome to spindle fibers through the kinetochore (a disc-shaped protein complex) for chromosome segregation in mitosis
Telomeres are specialized regions, at the ends of linear chromosomes, composed of repetitive nucleotide sequences that protect from degradation or fusion, and are maintained by telomerase (an enzyme) by extending the telomeres and adding repetitive sequences

Topic 13: Cell Cycle and Mitosis

The cell cycle encompasses G1, S, G2, and M phases, and its length varies based on cell type and external conditions
Prophase: Chromosomes condense, nuclear envelope breaks down, spindle apparatus forms
Prometaphase: Microtubules attach to chromosomes at the kinetochore. Kinetochores attach to microtubules from opposite poles for biorientation.
Metaphase: Chromosomes align at the metaphase plate (equidistant from the spindle poles).
Anaphase: Cohesins are cleaved by separase, and sister chromatids separate to opposite poles.
Telophase: Chromosomes decondense, and nuclear envelope reforms; cytokinesis completes the division into two daughter cells.
Checkpoints are mechanisms that regulate cell cycle progression to ensure DNA integrity and proper chromosome segregation (e.g., G1/S transition)
Cyclins and Cdks (Cyclin-Dependent Kinases) are regulatory proteins whose levels fluctuate during the cell cycle. Cyclins rise and fall following a specific pattern and bind to CDKs to become active kinase which phosphorylate target proteins to control the cell cycle.
Various checkpoints control progress, including G1/S, G2/M and metaphase/anaphase checkpoints, these checkpoints ensure that DNA is undamaged before replication and mitosis.
The spindle assembly checkpoint (SAC) ensures all chromosomes are properly attached to the spindle fibers before anaphase begins.

Topic 14: Meiosis

Meiosis involves two divisions (Meiosis I and II) resulting in four haploid daughter cells from one diploid parent cell
Homologous chromosomes undergo synapsis and crossing over (during Meiosis I) to exchange genetic material.
Sister chromatids separate in Meiosis II, similar to mitosis.

Topic 15: Apoptosis - Programmed Cell Death

Apoptosis is a form of controlled cell death, essential for normal development and tissue homeostasis, with regulated enzymatic cascades involved
The extrinsic pathway is triggered by external signals, like TNF-a or Fas ligand, binding to cell surface receptors.
The intrinsic pathway is triggered by internal signals, such as DNA damage or growth factor withdrawal, which can involve mitochondria and Bcl-2 family proteins (and subsequent cytochrome c release leading to caspase activation).
Caspases (enzymes) are crucial in the execution phase.
Caspase activation leads to cellular changes (nuclear fragmentation, DNA breakdown, membrane blebbing).
The apoptotic bodies are cleared by phagocytes, which prevent inflammation.

Topic 16: Stem Cells

Stem cells are characterized by self-renewal and differentiation potential
Totipotent stem cells can differentiate into all cell types and extraembryonic tissues.
Pluripotent stem cells can differentiate into all cell types but not extraembryonic tissues.
Multipotent stem cells can differentiate into several related cell types
Unipotent stem cells can differentiate into only one specific cell type.
Adult stem cells can be found in tissues with high turnover.

Topic 17: Cancer

Cancer results from uncontrolled cell growth and division—resulting in neoplasia formation.
Environmental factors like chemicals or radiation, viral infections, and genetic mutations can lead to cancer.
Oncogenes (mutated or overexpressed proto-oncogenes) drive cancer development (promoting proliferation).
Tumor suppressor genes prevent cancer by regulating cell division, repair, and apoptosis, like p53.
Mutations in proto-oncogenes or tumor suppressor genes can lead to uncontrolled cell division or prevention of appropriate cell death and hence cancer formation.
Cancer can be characterized by tumor formation, resulting in gene amplification or chromosomal translocations. Cancer can disrupt homeostasis in various ways.
Gleevec (imatinib) is a drug that targets the abnormal BCR-ABL kinase found in chronic myeloid leukemia (CML).
Tumorigenesis involves alterations in cellular pathways impacting proliferation, apoptosis, and senescence (including cell cycle pathways).
Various pathways are implicated in tumorigenesis, including oncogenes and tumor suppressor genes, like pathways that affect cell cycle regulation, apoptosis, and DNA repair, such as p53 and pRb and the effects of mutations to these genes influencing cancer development.

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