Chapter 3: Cell Structure and Theory
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Questions and Answers

During mitosis, what is the primary role of kinetochore microtubules?

  • To prevent chromosome condensation.
  • To lengthen the cell and push the poles apart.
  • To provide structural support to the spindle apparatus.
  • To attach to kinetochores and pull chromosomes to the cell's equator. (correct)

What distinguishes nonkinetochore microtubules from kinetochore microtubules during mitosis?

  • Nonkinetochore microtubules attach to the centromere of the chromosome.
  • There is no difference; the terms are interchangeable.
  • Nonkinetochore microtubules interact with each other to lengthen the cell, whereas kinetochore microtubules attach to chromosomes. (correct)
  • Nonkinetochore microtubules pull chromosomes to the poles, while kinetochore microtubules push the poles apart.

What would be the most likely outcome if the kinetochore microtubules failed to attach correctly during mitosis?

  • The chromosomes would still separate correctly due to the action of nonkinetochore microtubules.
  • One daughter cell might receive an incorrect number of chromosomes. (correct)
  • The cell cycle would be temporarily paused, allowing time for error correction.
  • Cytokinesis would occur normally, resulting in two healthy daughter cells.

If a drug inhibits the function of nonkinetochore microtubules, what is the most likely consequence during mitosis?

<p>The cell will not elongate as the poles are pushed apart. (B)</p> Signup and view all the answers

During the tug-of-war between kinetochore microtubules, what is the significance of both poles pulling on each chromosome?

<p>It helps align the chromosomes at the metaphase plate and ensures proper segregation. (D)</p> Signup and view all the answers

Which of the following best describes the principle of complementarity of structure and function in cells?

<p>Cell activities are dictated by their shapes and the types and relative numbers of subcellular structures they contain. (C)</p> Signup and view all the answers

What is the significance of the cell theory in biology?

<p>It establishes that cells are the fundamental units of life and that all cells come from pre-existing cells. (C)</p> Signup and view all the answers

A scientist is studying a new organism and observes that its cells lack specialized structures. Based on this observation, what can the scientist infer about the organism?

<p>The organism is likely a single-celled organism, like an amoeba. (A)</p> Signup and view all the answers

Which of the following statements accurately describes the relationship between cell shape and function?

<p>Cell shape is directly related to its specific function. (B)</p> Signup and view all the answers

What cellular process is responsible for the creation of most body cells?

<p>Mitosis (A)</p> Signup and view all the answers

If a scientist discovers that a particular disease is caused by a disruption in cellular homeostasis, which of the following would be a logical approach to developing a treatment?

<p>Develop a therapy to restore or support cellular homeostasis. (C)</p> Signup and view all the answers

Which of the following is NOT a key tenet of the cell theory?

<p>Cells can spontaneously generate from non-living matter. (A)</p> Signup and view all the answers

A researcher is comparing nerve cells and kidney tubule cells. What differences would they expect to find, based on the principle of complementarity?

<p>Nerve cells and kidney cells have different shapes and internal structures reflecting their different functions. (B)</p> Signup and view all the answers

Which of the following best describes the function of the nuclear lamina?

<p>Maintaining the shape of the nucleus and organizing DNA. (A)</p> Signup and view all the answers

How do molecules pass through the nuclear envelope?

<p>Through nuclear pores, with larger molecules requiring energy and transport proteins. (D)</p> Signup and view all the answers

Which of the following is NOT a component of chromatin?

<p>Ribosomal subunits (B)</p> Signup and view all the answers

What is the primary function of nucleoli?

<p>Assembly of ribosomal subunits. (B)</p> Signup and view all the answers

What happens to a cell if its nucleus is removed?

<p>It cannot synthesize proteins and will eventually deteriorate. (A)</p> Signup and view all the answers

What is the role of histone proteins in chromatin?

<p>To package and regulate DNA. (D)</p> Signup and view all the answers

How does the nuclear envelope differ from other cellular membranes?

<p>It is selectively permeable with relatively large pores for easier passage of substances. (A)</p> Signup and view all the answers

What is the significance of multinucleated cells?

<p>They signify regulation of a larger-than-usual cytoplasmic mass. (C)</p> Signup and view all the answers

What is the role of the nuclear pore complex?

<p>To line each pore, forming a transport channel and regulating entry and exit of molecules. (A)</p> Signup and view all the answers

Which of the following accurately describes the function of epithelial cells?

<p>Protecting underlying tissues from bacterial invasion. (C)</p> Signup and view all the answers

How do ribosomal subunits get from the nucleolus, where they are assembled, to the cytoplasm, where they function?

<p>They are transported through the nuclear pores. (A)</p> Signup and view all the answers

If a cell is actively producing tissue proteins, what would you expect to observe about its nucleoli?

<p>They would be larger than usual. (B)</p> Signup and view all the answers

What is the primary role of extracellular fluid (ECF) within the body?

<p>To dissolve and transport substances throughout the body. (D)</p> Signup and view all the answers

What is the arrangement of DNA around nucleosomes?

<p>DNA winds twice around each nucleosome core. (A)</p> Signup and view all the answers

How do cilia contribute to the function of cells lining the respiratory tract?

<p>They propel mucus containing dust and bacteria away from the lungs. (B)</p> Signup and view all the answers

Considering its function, which of the following cell types would you expect to lack a nucleus at maturity?

<p>Red blood cells (A)</p> Signup and view all the answers

What structural arrangement of microtubules is characteristic of cilia?

<p>A central pair surrounded by nine outer doublets. (D)</p> Signup and view all the answers

What is the composition of the fluid within the nucleus?

<p>Nucleoplasm (C)</p> Signup and view all the answers

How do the actin filaments in microvilli contribute to their function?

<p>They act as a mechanical 'stiffener' to shape the cell. (C)</p> Signup and view all the answers

If a drug were designed to interfere with the assembly of ribosomal subunits, which specific nuclear structure would be its primary target?

<p>Nucleolus (B)</p> Signup and view all the answers

Which cellular component is directly involved in the formation of cilia?

<p>Centrioles (A)</p> Signup and view all the answers

How does the arrangement of microtubules in the basal body differ from that in the cilium itself?

<p>The basal body contains nine triplets, while the cilium contains a '9 + 2' arrangement. (B)</p> Signup and view all the answers

What distinguishes microvilli from cilia in terms of structure and primary function?

<p>Microvilli increase surface area for absorption, while cilia are motile and move substances. (C)</p> Signup and view all the answers

Which of the following is an example of a cell that contains microvilli?

<p>Intestinal Cell (C)</p> Signup and view all the answers

If a cell were unable to produce a functional terminal web, what would be the most likely consequence?

<p>Impaired structural support for microvilli. (C)</p> Signup and view all the answers

Which of the following is NOT considered a main part of a human cell?

<p>Extracellular matrix (D)</p> Signup and view all the answers

What is the primary function of the nucleus within a cell?

<p>Controlling cellular activities. (D)</p> Signup and view all the answers

Which component of the extracellular fluid directly bathes the cells in tissues, providing them with nutrients and regulatory substances?

<p>Interstitial fluid (C)</p> Signup and view all the answers

What would be the most likely effect on ciliary function if the cross-linking proteins between outer doublets were non-functional?

<p>Cilia would be unable to generate the power stroke. (B)</p> Signup and view all the answers

An individual has a genetic defect that impairs the production of extracellular matrix components. How might this affect tissue function?

<p>Reduced structural support and cell communication. (C)</p> Signup and view all the answers

What is the main role of mRNA in protein synthesis?

<p>To carry the coded information from DNA to the cytoplasm for protein synthesis. (D)</p> Signup and view all the answers

If a gene contains 300 base pairs, approximately how many amino acids would you expect the corresponding polypeptide to contain?

<p>100 (C)</p> Signup and view all the answers

How do introns contribute to genetic diversity and evolution?

<p>By providing raw material for rapid evolution by allowing exons to be swapped from gene to gene. (B)</p> Signup and view all the answers

Which of the following is NOT a characteristic of RNA?

<p>It is typically double-stranded. (C)</p> Signup and view all the answers

What is the role of tRNA in protein synthesis?

<p>To ferry amino acids to the ribosomes and decode mRNA's message. (A)</p> Signup and view all the answers

During which process is DNA's information encoded in mRNA?

<p>Transcription (C)</p> Signup and view all the answers

What is the key event that occurs during translation?

<p>The information carried by mRNA is decoded and used to assemble polypeptides. (D)</p> Signup and view all the answers

Which of the following best describes the function of exons?

<p>They code for protein. (A)</p> Signup and view all the answers

A mutation occurs in a gene, changing a codon from AAA to AAG. Both codons specify the amino acid lysine. What type of mutation is this?

<p>Silent mutation (D)</p> Signup and view all the answers

What would be the most likely outcome if a cell's tRNA molecules were unable to bind amino acids?

<p>Polypeptide synthesis would stop. (A)</p> Signup and view all the answers

What is the significance of the fact that our 20,000 genes are located on only about 2% of the nuclear DNA?

<p>It suggests that non-coding regions of DNA may have regulatory or other functions. (D)</p> Signup and view all the answers

If a DNA template strand has the sequence 3'-TTCAGTCGT-5', what would be the sequence of the corresponding mRNA strand?

<p>5'-AAGTCAGCA-3' (C)</p> Signup and view all the answers

Which of the following correctly identifies the roles of the three types of RNA?

<p>mRNA: carries coded information; rRNA: forms ribosomes; tRNA: carries amino acids (D)</p> Signup and view all the answers

What is the functional significance of the long-lived nature of rRNA and tRNA compared to mRNA?

<p>It ensures a constant supply of ribosomes and tRNA for protein synthesis. (A)</p> Signup and view all the answers

What is the primary reason DNA does not leave the nucleus in eukaryotic cells?

<p>DNA is too large to pass through the nuclear pores. (A)</p> Signup and view all the answers

Which of the following modifications to histone proteins would likely result in increased gene expression?

<p>Addition of acetyl groups, promoting extended chromatin. (D)</p> Signup and view all the answers

A cell with a high metabolic activity would likely display which characteristic regarding its chromatin?

<p>A higher proportion of extended chromatin to facilitate transcription. (B)</p> Signup and view all the answers

During which stage of cell division does cytokinesis typically begin?

<p>Anaphase (B)</p> Signup and view all the answers

What is accomplished by the coiling and condensation of chromatin into chromosomes during cell division?

<p>It protects delicate DNA strands from tangling and breaking during cell division. (A)</p> Signup and view all the answers

If a gene has the base sequence 'TACGCA' on the template strand of DNA, what is the corresponding base sequence on the mRNA transcript?

<p>AUGCCU (C)</p> Signup and view all the answers

Which event is directly facilitated by the presence of a contractile ring during cell division?

<p>Formation of the cleavage furrow to divide the cell. (C)</p> Signup and view all the answers

Which of the following cell types typically retains the ability to divide and regenerate, even in mature tissues?

<p>Cells of the intestinal lining. (B)</p> Signup and view all the answers

Considering its function, where would you expect to find the highest concentration of rRNA being produced?

<p>In the ribosomes, where proteins are synthesized. (D)</p> Signup and view all the answers

What is the significance of the triplet code in DNA?

<p>It specifies the sequence of amino acids in a polypeptide chain. (C)</p> Signup and view all the answers

Which of the following represents the correct order of events during the M phase of the cell cycle?

<p>Prophase, Metaphase, Anaphase, Telophase (C)</p> Signup and view all the answers

A mutation occurs in a gene that codes for a protein responsible for regulating the cell cycle. What is a likely consequence of this mutation?

<p>Uncontrolled cell division. (C)</p> Signup and view all the answers

How do daughter cells produced through mitosis compare to the parent cell?

<p>They are genetically identical, with the same number of chromosomes. (A)</p> Signup and view all the answers

Which process is directly responsible for producing sex cells (ova and sperm) with only half the number of genes found in other body cells?

<p>Meiosis (B)</p> Signup and view all the answers

Given the following mRNA codon sequence: 5'-AUG-GCA-UAC-3', how many amino acids would be present in the resulting peptide, assuming the entire sequence is translated?

<p>3 (B)</p> Signup and view all the answers

Flashcards

Kinetochores

Protein structures on chromosomes where microtubules attach during cell division.

Kinetochore Microtubules

Microtubules that attach to kinetochores, pulling chromosomes during mitosis.

Nonkinetochore Microtubules

Microtubules that don't attach to kinetochores, but help elongate the cell during mitosis.

Mitosis

The division of the nucleus in eukaryotic cells, resulting in two identical daughter nuclei.

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Centromere

The point on a chromosome where sister chromatids are joined.

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Cell

The basic structural and functional unit of all living organisms.

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Cell Theory

All organisms are made of one or more cells; the cell is the basic unit of life; and cells arise from pre-existing cells.

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Cells as Building Blocks

Cells are the structural and functional building blocks of an organism.

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Cellular Activity

The activity of an organism depends on the combined activities of its individual cells.

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Complementarity of Structure and Function

The principle that a cell's function is dictated by its shape and the subcellular structures it contains.

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Cell Origin

Cells arise from other cells through cell division.

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Homeostasis

The maintenance of a stable internal environment within a cell or organism.

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Epithelial Cells

Flat, tile-like cells forming a barrier that protects underlying tissues.

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Nerve Cell

Gathers information and controls body functions.

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Sperm Cell

Cell of reproduction.

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Skeletal Muscle Cell

Cells that move organs and body parts.

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Fat Cell

Cell that stores nutrients.

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Immune Cell

Cell that fights disease.

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Plasma Membrane

The outer boundary of the cell, acting as a selectively permeable barrier.

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Cytoplasm

Intracellular fluid packed with organelles.

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Nucleus

Organelle that controls cellular activities.

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Extracellular Materials

Substances found outside the cells contributing to body mass.

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Interstitial Fluid

Fluid that bathes cells, containing nutrients and wastes.

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Cilia

Whiplike extensions that move substances across cell surfaces.

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Microvilli

Tiny extensions that increase the plasma membrane surface area for absorption.

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Centrioles (cilia formation)

Multiply and line up beneath the plasma membrane at the cell's free (exposed) surface

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"9 + 2" arrangement

Arrangement of microtubules in cilia

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Triplet Code

A sequence of three DNA bases that specifies a particular amino acid.

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Exons

Regions of DNA that code for proteins

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Introns

Non-coding regions of DNA between exons.

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RNA

Acts as a decoder and messenger of genetic information. Single-stranded nucleic acid that contains ribose.

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mRNA

Carries coded information from DNA to ribosomes for protein synthesis.

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rRNA

Forms ribosomes, which are the sites of protein synthesis.

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tRNA

Transports amino acids to the ribosomes and decodes the mRNA sequence

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Transcription

DNA information is encoded in mRNA.

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Translation

mRNA information is decoded and used to assemble polypeptides.

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RNA Processing

Modification where introns are removed from pre-mRNA.

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Interphase

Period of the cell cycle when the cell grows and performs its normal functions.

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Chromatin

DNA-containing material in a non-dividing cell.

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Centrosome

Structure that organizes microtubules and helps form the spindle during cell division.

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Chromosome

Condensed form of DNA, consisting of two sister chromatids.

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Mitotic Spindle

The microtubule assembly responsible for moving and separating chromosomes during mitosis.

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Condensed Chromatin

Inactive, condensed regions of chromatin that stain darker and are easily visible under a light microscope.

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Extended Chromatin

Active regions of chromatin where DNA segments are exposed for protein synthesis.

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M (Mitotic) Phase

Cell division resulting in two daughter cells; includes mitosis and cytokinesis.

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Cytokinesis

Division of the cytoplasm, resulting in two separate daughter cells.

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Messenger RNA (mRNA)

Carries instructions from DNA for building proteins.

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Gene

Segment of DNA that carries instructions for creating one polypeptide chain.

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Triplet

Sequence of three nucleotide bases in DNA that specifies a particular amino acid.

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Cell Cycle Control Factors

Regulate when cells divide or stop dividing; can be internal or external.

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Histone Acetylation

Addition of acetyl groups to histone proteins, exposing DNA segments for gene expression.

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Histone Methylation

Addition of methyl groups to histone proteins, shutting down nearby DNA.

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Mitosis as a Continuous Process

A continuous process with phases (prophase, metaphase, anaphase, telophase) that blend smoothly.

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Scar tissue

A fibrous connective tissue that replaces damaged cells in nervous tissue, skeletal muscle, and heart muscle that have lost ability to divide.

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DNA blueprint for protein synthesis

DNA serves as the master blueprint for protein synthesis. Each sequence specifies a particular amino acid.

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Multinucleate Cells

Cells having multiple nuclei.

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Anucleate Cells

Cells lacking a nucleus.

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Nuclear Envelope

The double membrane barrier surrounding the nucleus.

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Nuclear Lamina

The protein network lining the inner nuclear membrane, maintaining shape and organizing DNA.

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Nuclear Pores

Protein complexes that punctures the nuclear envelope, regulating transport in and out of the nucleus.

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Nucleoplasm

The jelly-like fluid within the nucleus.

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Nucleoli

Dark-staining spherical bodies in the nucleus where ribosomal subunits are assembled.

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Nucleoli function

Aggregations of components needed to synthesize and assemble ribosomal subunits.

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Chromatin Composition

DNA, histone proteins, and RNA chains.

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Nucleosomes

Fundamental units of chromatin consisting of histone protein clusters connected by DNA.

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Histone Proteins

Globular proteins that package and regulate DNA.

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Linker DNA

Segments of DNA connecting nucleosomes.

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Nuclear Transport

The process of substances passing freely through nuclear pore complexes.

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Study Notes

  • Cells, the structural units of all living things, range from single-celled organisms to complex multicellular ones.
  • The human body comprises 50 to 100 trillion cells.
  • Cells are the smallest unit of life.
  • Cell research has defined the cell theory.
  • The cell theory includes these concepts:

Cell Theory

  • The cell embodies the smallest unit of life.
  • Organisms consist of one or more cells.
  • Cells arise from existing cells
  • Loss of cellular homeostasis underlies virtually every disease.
  • Over 250 types of cells exist in the human body, varying in shape, size, and function.
  • Cell shapes correlate with their functions, such as flat epithelial cells forming protective barriers.

Generalized Cell Structure

  • A generalized cell has three main parts: the plasma membrane, cytoplasm, and nucleus.
  • Plasma membrane: the outer boundary of the cell, acts as a selectively permeable barrier.
  • Cytoplasm: intracellular fluid with organelles that perform specific cell functions.
  • Nucleus: an organelle that controls cellular activities.

Extracellular Materials

  • Extracellular materials contribute to body mass and are located outside the cells.
  • Major classes of extracellular materials include:
    • Extracellular fluid: transports substances, including interstitial fluid that bathes cells.
    • Interstitial fluid contains amino acids, sugars, fatty acids, regulatory substances, and wastes.

Cilia and Flagella

  • Cilia are whiplike extensions that move substances across cell surfaces.
    • Cilia are abundant on exposed cell surfaces.
    • Cilia beat in coordinated waves.
  • Cilia originate from centrioles beneath the plasma membrane.
    • They have a "9 + 2" arrangement of microtubules in cross section.
  • Ciliary motion involves a power stroke and a recovery stroke, repeating 10 to 20 times per second.
  • Microvilli are fingerlike extensions of the plasma membrane, they increase surface area for absorption.
    • Commonly found on absorptive cells in the intestines and kidneys.
    • Contain actin filaments for stiffening.

Nucleus Structure

  • The nucleus is the cell's control center, it contains genetic instructions
  • Most cells have one nucleus, while some have many, this signifies a need to regulate a larger cytoplasmic mass.
  • Mature red blood cells lack nuclei, and cannot reproduce.
  • The nucleus consists of the nuclear envelope, nucleoli, and chromatin.
  • Nuclear envelope: a double membrane barrier with pores for transport.
    • The outer membrane is continuous with the endoplasmic reticulum and the inner membrane lined by the nuclear lamina.
    • Nuclear pores regulate the entry and exit of molecules.
  • Nucleoplasm: the jellylike fluid within the nucleus.
  • Nucleoli: dark-staining bodies where ribosomal subunits are assembled, they contain DNA coding for ribosomal RNA (rRNA).
  • Chromatin: composed of DNA, histone proteins, and RNA.
    • Histones compact DNA, regulate genes.
    • Nucleosomes: the fundamental units of chromatin.
    • Extended chromatin segments are active.
    • Condensed chromatin segments, or chromosomes, are inactive.

Cell Division

  • Cell division is essential for body growth and tissue repair.
  • The M (mitotic) phase involves mitosis and cytokinesis.

Mitosis

  • Mitosis divides the nucleus, distributing replicated DNA to two daughter cells, divided into prophase, metaphase, anaphase, and telophase.

Cytokinesis

  • Cytokinesis divides the cytoplasm, completing after mitosis, it pinches the cell into two daughter cells.

Protein Synthesis

  • DNA serves as the blueprint for protein synthesis
  • A gene is a DNA segment that carries instructions for creating a polypeptide chain.
  • Every three-base sequence is a triplet, it specifies an amino acid.
  • Genes include coding regions (exons) and non-coding regions (introns).

Role of RNA in Protein Synthesis

  • RNA decodes the DNA message and carries it to ribosomes.
  • RNA has uracil (U) instead of thymine (T).
  • Three forms of RNA mediate protein synthesis:
    • Messenger RNA (mRNA): carries coded information for protein structure.
    • Ribosomal RNA (rRNA): forms the ribosomes.
    • Transfer RNA (tRNA): transfers amino acids to the ribosomes.
  • RNA forms on DNA and migrates into the cytoplasm.

Polypeptide synthesis steps

  • Polypeptide synthesis involves transcription (DNA to mRNA) and translation (mRNA to polypeptide).

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Explore the fundamental structure of cells, the smallest units of life, and the principles of cell theory. Learn about the components of a generalized cell, including the plasma membrane, cytoplasm, and nucleus, and their functions. Understand the importance of cellular homeostasis and the diversity of cell types in the human body.

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