Explică modul în care diferențierea celulară leagă controlul genetic de apariția unor celule cu forme și funcții specializate. Include exemplul precursorilor celulelor musculare.
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Answer: În timpul diferențierii, celulele exprimă predominant seturi diferite de gene, care controlează activități citoplasmatice specifice. Această expresie selectivă a genelor organizează celulele pentru funcții specializate și le poate schimba forma. De exemplu, precursorii celulelor musculare se alungesc, devenind celule asemănătoare fibrelor, și acumulează rețele mari de actină și miozină, adaptate producerii contracțiilor.
Celulele organismului provin din același zigot, dar diferențierea le permite să folosească seturi distincte de gene. În celulele musculare, expresia genelor asociate actinei și miozinei contribuie la forma alungită și la capacitatea de contracție.
Fill in the blank
Nucleul conține ___, masa formată din ADN și proteinele asociate, precum și una sau mai multe regiuni specializate ale cromatinei numite ___.
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Answer: Blank 1: cromatină (se acceptă și cromatina). Blank 2: nucleoli (se acceptă și nucleole).
Cromatina reprezintă ADN-ul împreună cu proteinele asociate, iar nucleolii sunt regiuni specializate ale cromatinei din nucleu.
Single choice
Cum se numesc celulele rezultate din primele diviziuni ale zigotului?
Blastomere
Celule epiteliale
Miocite mature
Celule secretoare
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Answer: Blastomere
Primele diviziuni celulare ale zigotului produc blastomere. Ulterior, majoritatea celulelor fetale trec prin diferențiere și dobândesc caracteristici specializate.
Multiple choice
Care afirmații descriu corect nucleul unei celule?
Conține cromatina, formată din ADN și proteine asociate.
Conține mecanismele moleculare pentru replicarea ADN-ului.
Conține mecanismele pentru sinteza și procesarea tuturor tipurilor de ARN.
Este principalul loc al sintezei ATP-ului.
Conține hidrolaze acide pentru degradarea macromoleculelor celulare.
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Answer: Conține cromatina, formată din ADN și proteine asociate. · Conține mecanismele moleculare pentru replicarea ADN-ului. · Conține mecanismele pentru sinteza și procesarea tuturor tipurilor de ARN.
Nucleul conține cromatina și coordonează procesele genetice, inclusiv replicarea ADN-ului și sinteza și procesarea ARN-ului. Sinteza majorității ATP-ului are loc în mitocondrii, iar hidrolazele acide se găsesc în lizozomi.
Single choice
În imaginea generată, care structură este cel mai probabil centrul de control genetic al celulei?
Nucleul
Lizozomul
Peroxizomul
Ribozomul
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Answer: Nucleul
Nucleul este de obicei o structură mare, rotundă sau ovală, situată adesea în apropierea centrului celulei, și conține materialul genetic și mecanismele necesare pentru controlul activității celulare.
Endoplasmic Reticulum and Golgi Apparatus
Fill in the blank
The rough endoplasmic reticulum has a granular, basophilic cytoplasmic surface because of attached ___, whereas the smooth endoplasmic reticulum lacks ___.
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Answer: Blank 1: polysomes or ribosomes; Blank 2: ribosomes or polysomes.
Polysomes attached to the rough endoplasmic reticulum produce its granular, basophilic appearance. The smooth endoplasmic reticulum lacks ribosomes and instead contains enzymes involved in lipid and glycogen metabolism, detoxification, and temporary calcium sequestration.
Single choice
A cell actively secretes proteins but has relatively little need for lipid synthesis or detoxification. Which organelle would be expected to be especially well developed?
Rough endoplasmic reticulum
Smooth endoplasmic reticulum
Peroxisome
Lysosome
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Answer: Rough endoplasmic reticulum
The rough endoplasmic reticulum is well developed in cells that actively secrete proteins because its polysomes synthesize proteins destined for exocytosis, membranes, or certain organelles.
Multiple choice
Which functions are characteristic of the Golgi apparatus?
Further enzymatic modification of proteins received from the rough endoplasmic reticulum
Packaging modified proteins into vesicles
Directing vesicles toward lysosomes, the plasma membrane, or secretion
Translation of messenger RNA into protein by ribosomes attached to its membrane
Degradation of improperly folded proteins after ubiquitin tagging
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Answer: Further enzymatic modification of proteins received from the rough endoplasmic reticulum · Packaging modified proteins into vesicles · Directing vesicles toward lysosomes, the plasma membrane, or secretion
The Golgi apparatus modifies, sorts, and packages proteins arriving from the rough endoplasmic reticulum. Translation is performed by ribosomes, whereas ubiquitin-tagged improperly folded proteins are degraded by proteasomes.
Flash card
Describe the pathway followed by a protein that is synthesized for secretion outside the cell, beginning with its synthesis and ending with its release.
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Answer: The protein is synthesized by polysomes associated with the rough endoplasmic reticulum and translocated into the cisterna, where it folds and undergoes post-translational modification. It is then transported in vesicles to the Golgi apparatus, where it undergoes further modifications, moves through the Golgi cisternae, and is packaged into vesicles that fuse with the plasma membrane and release it by exocytosis.
Secreted proteins move through the rough endoplasmic reticulum and Golgi apparatus in sequence. The rough endoplasmic reticulum supports synthesis, translocation, folding, and initial modification, while the Golgi apparatus performs additional modification and packaging before exocytosis.
Cytoskeleton
Fill in the blank
The three main types of cytoskeletal polymers are ___, ___, and ___.
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Answer: Blank 1: microtubules. Blank 2: actin filaments or microfilaments. Blank 3: intermediate filaments. Accept equivalent wording and common capitalization variants.
The cytoskeleton contains microtubules, actin filaments or microfilaments, and intermediate filaments.
Numeric
A cytoskeletal structure serving as a transport track is measured across its diameter. What approximate diameter would identify it as a microtubule?
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Answer: Value: 25 nm (accept approximately 23–27 nm).
Microtubules have an approximate diameter of 25 nm, making them wider than actin filaments at 5–7 nm and intermediate filaments at 8–10 nm.
Multiple choice
Which statements correctly describe functions or properties of microtubules?
They help maintain cell shape.
They serve as tracks for transporting vesicles and organelles.
Their transport functions involve the motor proteins kinesin and dynein.
They are flexible filaments made from actin subunits.
They produce cytoplasmic movement by binding directly to actin through myosin.
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Answer: They help maintain cell shape. · They serve as tracks for transporting vesicles and organelles. · Their transport functions involve the motor proteins kinesin and dynein.
Microtubules help maintain cell shape and provide tracks for intracellular transport by kinesin and dynein. They are made from tubulin, whereas actin filaments and myosins are central to many cytoplasmic movements.
Single choice
In the generated diagram, which cytoskeletal polymer is represented by the hollow, semirigid tubular structure?
Microtubules
Actin filaments
Intermediate filaments
Myosin bundles
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Answer: Microtubules
Microtubules are semirigid tubular structures whose walls are composed of polymerized tubulin heterodimers.
Flash card
A cell is migrating across a substrate and must also constrict during cell cleavage after mitosis. Which cytoskeletal components are especially important for these activities, and how do they contribute?
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Answer: Actin filaments and myosins are especially important. Actin filaments form dynamic structures, while myosins bind to and move along them, producing cytoplasmic movement. These interactions contribute to cell locomotion and cell cleavage after mitosis.
Actin–myosin interactions generate movement in the cytoplasm. The study material specifically identifies their roles in cell locomotion and cleavage after mitosis.
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