Module 3: The Cellular Level of Organization

Lesson 6: Cell Growth and Division

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Dưới đây là danh sách những thuật ngữ Y khoa của module The Cellular Level of Organization.
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Medical Terminology: The Cellular Level of Organization

active transport
form of transport across the cell membrane that requires input of cellular energy
amphipathic
describes a molecule that exhibits a difference in polarity between its two ends, resulting in a difference in water solubility
anaphase
third stage of mitosis (and meiosis), during which sister chromatids separate into two new nuclear regions of a dividing cell
anticodon
consecutive sequence of three nucleotides on a tRNA molecule that is complementary to a specific codon on an mRNA molecule
autolysis
breakdown of cells by their own enzymatic action
autophagy
lysosomal breakdown of a cell’s own components
cell cycle
life cycle of a single cell, from its birth until its division into two new daughter cells
cell membrane
membrane surrounding all animal cells, composed of a lipid bilayer interspersed with various molecules; also known as plasma membrane
centriole
small, self-replicating organelle that provides the origin for microtubule growth and moves DNA during cell division
centromere
region of attachment for two sister chromatids
centrosome
cellular structure that organizes microtubules during cell division
channel protein
membrane-spanning protein that has an inner pore which allows the passage of one or more substances
checkpoint
progress point in the cell cycle during which certain conditions must be met in order for the cell to proceed to a subsequence phase
chromatin
substance consisting of DNA and associated proteins
chromosome
condensed version of chromatin
cilia
small appendage on certain cells formed by microtubules and modified for movement of materials across the cellular surface
cleavage furrow
contractile ring that forms around a cell during cytokinesis that pinches the cell into two halves
codon
consecutive sequence of three nucleotides on an mRNA molecule that corresponds to a specific amino acid
concentration gradient
difference in the concentration of a substance between two regions
cyclin
one of a group of proteins that function in the progression of the cell cycle
cyclin-dependent kinase (CDK)
one of a group of enzymes associated with cyclins that help them perform their functions
cytokinesis
final stage in cell division, where the cytoplasm divides to form two separate daughter cells
cytoplasm
internal material between the cell membrane and nucleus of a cell, mainly consisting of a water-based fluid called cytosol, within which are all the other organelles and cellular solute and suspended materials
cytoskeleton
“skeleton” of a cell; formed by rod-like proteins that support the cell’s shape and provide, among other functions, locomotive abilities
cytosol
clear, semi-fluid medium of the cytoplasm, made up mostly of water
diffusion
movement of a substance from an area of higher concentration to one of lower concentration
diploid
condition marked by the presence of a double complement of genetic material (two sets of chromosomes, one set inherited from each of two parents)
DNA polymerase
enzyme that functions in adding new nucleotides to a growing strand of DNA during DNA replication
DNA replication
process of duplicating a molecule of DNA
electrical gradient
difference in the electrical charge (potential) between two regions
endocytosis
import of material into the cell by formation of a membrane-bound vesicle
endoplasmic reticulum (ER)
cellular organelle that consists of interconnected membrane-bound tubules, which may or may not be associated with ribosomes (rough type or smooth type, respectively)
exocytosis
export of a substance out of a cell by formation of a membrane-bound vesicle
exon
one of the coding regions of an mRNA molecule that remain after splicing
extracellular fluid (ECF)
fluid exterior to cells; includes the interstitial fluid, blood plasma, and fluid found in other reservoirs in the body
facilitated diffusion
diffusion of a substance with the aid of a membrane protein
flagellum
appendage on certain cells formed by microtubules and modified for movement
G0 phase
phase of the cell cycle, usually entered from the G1 phase; characterized by long or permanent periods where the cell does not move forward into the DNA synthesis phase
G1 phase
first phase of the cell cycle, after a new cell is born
G2 phase
third phase of the cell cycle, after the DNA synthesis phase
gene
functional length of DNA that provides the genetic information necessary to build a protein
gene expression
active interpretation of the information coded in a gene to produce a functional gene product
genome
entire complement of an organism’s DNA; found within virtually every cell
glycocalyx
coating of sugar molecules that surrounds the cell membrane
glycoprotein
protein that has one or more carbohydrates attached
Golgi apparatus
cellular organelle formed by a series of flattened, membrane-bound sacs that functions in protein modification, tagging, packaging, and transport
helicase
enzyme that functions to separate the two DNA strands of a double helix during DNA replication
histone
family of proteins that associate with DNA in the nucleus to form chromatin
homologous
describes two copies of the same chromosome (not identical), one inherited from each parent
hydrophilic
describes a substance or structure attracted to water
hydrophobic
describes a substance or structure repelled by water
hypertonic
describes a solution concentration that is higher than a reference concentration
hypotonic
describes a solution concentration that is lower than a reference concentration
integral protein
membrane-associated protein that spans the entire width of the lipid bilayer
intermediate filament
type of cytoskeletal filament made of keratin, characterized by an intermediate thickness, and playing a role in resisting cellular tension
interphase
entire life cycle of a cell, excluding mitosis
interstitial fluid (IF)
fluid in the small spaces between cells not contained within blood vessels
intracellular fluid (ICF)
fluid in the cytosol of cells
intron
non-coding regions of a pre-mRNA transcript that may be removed during splicing
isotonic
describes a solution concentration that is the same as a reference concentration
kinetochore
region of a centromere where microtubules attach to a pair of sister chromatids
ligand
molecule that binds with specificity to a specific receptor molecule
lysosome
membrane-bound cellular organelle originating from the Golgi apparatus and containing digestive enzymes
messenger RNA (mRNA)
nucleotide molecule that serves as an intermediate in the genetic code between DNA and protein
metaphase
second stage of mitosis (and meiosis), characterized by the linear alignment of sister chromatids in the center of the cell
metaphase plate
linear alignment of sister chromatids in the center of the cell, which takes place during metaphase
microfilament
the thinnest of the cytoskeletal filaments; composed of actin subunits that function in muscle contraction and cellular structural support
microtubule
the thickest of the cytoskeletal filaments, composed of tubulin subunits that function in cellular movement and structural support
mitochondrion
one of the cellular organelles bound by a double lipid bilayer that function primarily in the production of cellular energy (ATP)
mitosis
division of genetic material, during which the cell nucleus breaks down and two new, fully functional, nuclei are formed
mitotic phase
phase of the cell cycle in which a cell undergoes mitosis
mitotic spindle
network of microtubules, originating from centrioles, that arranges and pulls apart chromosomes during mitosis
multipotent
describes the condition of being able to differentiate into different types of cells within a given cell lineage or small number of lineages, such as a red blood cell or white blood cell
mutation
change in the nucleotide sequence in a gene within a cell’s DNA
nuclear envelope
membrane that surrounds the nucleus; consisting of a double lipid-bilayer
nuclear pore
one of the small, protein-lined openings found scattered throughout the nuclear envelope
nucleolus
small region of the nucleus that functions in ribosome synthesis
nucleosome
unit of chromatin consisting of a DNA strand wrapped around histone proteins
nucleus
cell’s central organelle; contains the cell’s DNA
oligopotent
describes the condition of being more specialized than multipotency; the condition of being able to differentiate into one of a few possible cell types
organelle
any of several different types of membrane-enclosed specialized structures in the cell that perform specific functions for the cell
osmosis
diffusion of water molecules down their concentration gradient across a selectively permeable membrane
passive transport
form of transport across the cell membrane that does not require input of cellular energy
peripheral protein
membrane-associated protein that does not span the width of the lipid bilayer, but is attached peripherally to integral proteins, membrane lipids, or other components of the membrane
peroxisome
membrane-bound organelle that contains enzymes primarily responsible for detoxifying harmful substances
phagocytosis
endocytosis of large particles
pinocytosis
endocytosis of fluid
pluripotent
describes the condition of being able to differentiate into a large variety of cell types
polypeptide
chain of amino acids linked by peptide bonds
polyribosome
simultaneous translation of a single mRNA transcript by multiple ribosomes
promoter
region of DNA that signals transcription to begin at that site within the gene
prophase
first stage of mitosis (and meiosis), characterized by breakdown of the nuclear envelope and condensing of the chromatin to form chromosomes
proteome
full complement of proteins produced by a cell (determined by the cell’s specific gene expression)
reactive oxygen species (ROS)
a group of extremely reactive peroxides and oxygen-containing radicals that may contribute to cellular damage
receptor
protein molecule that contains a binding site for another specific molecule (called a ligand)
receptor-mediated endocytosis
endocytosis of ligands attached to membrane-bound receptors
ribosomal RNA (rRNA)
RNA that makes up the subunits of a ribosome
ribosome
cellular organelle that functions in protein synthesis
RNA polymerase
enzyme that unwinds DNA and then adds new nucleotides to a growing strand of RNA for the transcription phase of protein synthesis
S phase
stage of the cell cycle during which DNA replication occurs
selective permeability
feature of any barrier that allows certain substances to cross but excludes others
sister chromatid
one of a pair of identical chromosomes, formed during DNA replication
sodium-potassium pump
(also, Na+/K+ ATP-ase) membrane-embedded protein pump that uses ATP to move Na+ out of a cell and K+ into the cell
somatic cell
all cells of the body excluding gamete cells
spliceosome
complex of enzymes that serves to splice out the introns of a pre-mRNA transcript
splicing
the process of modifying a pre-mRNA transcript by removing certain, typically non-coding, regions
stem cell
cell that is oligo-, multi-, or pleuripotent that has the ability to produce additional stem cells rather than becoming further specialized
telophase
final stage of mitosis (and meiosis), preceding cytokinesis, characterized by the formation of two new daughter nuclei
totipotent
embryonic cells that have the ability to differentiate into any type of cell and organ in the body
transcription
process of producing an mRNA molecule that is complementary to a particular gene of DNA
transcription factor
one of the proteins that regulate the transcription of genes
transfer RNA (tRNA)
molecules of RNA that serve to bring amino acids to a growing polypeptide strand and properly place them into the sequence
translation
process of producing a protein from the nucleotide sequence code of an mRNA transcript
triplet
consecutive sequence of three nucleotides on a DNA molecule that, when transcribed into an mRNA codon, corresponds to a particular amino acid
unipotent
describes the condition of being committed to a single specialized cell type
vesicle
membrane-bound structure that contains materials within or outside of the cell
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Dưới đây là các bài văn nằm ở bên trái. Ở bên phải là các bài luyện tập (practice) để đánh giá khả năng đọc hiểu của bạn. Sẽ khó khăn trong thời gian đầu nếu vốn từ vựng của bạn còn hạn chế, đặc biệt là từ vựng Y khoa. Hãy kiên nhẫn và đọc nhiều nhất có kể, lượng kiến thức tích tụ dần sẽ giúp bạn đọc thoải mái hơn.
Cell division is a fundamental biological process crucial for the growth, development, and maintenance of all living organisms. While there are a few cells in the body that do not undergo cell division (such as gametes, red blood cells, most neurons, and some muscle cells), most somatic cells divide regularly. A somatic cell is a general term for a body cell, and all human cells, except for the cells that produce eggs and sperm (which are referred to as germ cells), are somatic cells. Somatic cells contain two copies of each of their chromosomes (one copy received from each parent). A homologous pair of chromosomes is the two copies of a single chromosome found in each somatic cell. The human is a diploid organism, having 23 homologous pairs of chromosomes in each of the somatic cells. The condition of having pairs of chromosomes is known as diploidy.

Cells in the body replace themselves over the lifetime of a person. For example, the cells lining the gastrointestinal tract must be frequently replaced when constantly “worn off” by the movement of food through the gut. But what triggers a cell to divide, and how does it prepare for and complete cell division? The cell cycle is the sequence of events in the life of the cell from the moment it is created at the end of a previous cycle of cell division until it then divides itself, generating two new cells.
One “turn” or cycle of the cell cycle consists of two general phases: interphase, followed by mitosis and cytokinesis. Interphase is the period of the cell cycle during which the cell is not dividing. The majority of cells are in interphase most of the time. Mitosis is the division of genetic material, during which the cell nucleus breaks down and two new, fully functional, nuclei are formed. Cytokinesis divides the cytoplasm into two distinctive cells.

A. Interphase

A cell grows and carries out all normal metabolic functions and processes in a period called G1 (Figure 1). G1 phase (gap 1 phase) is the first gap, or growth phase in the cell cycle. For cells that will divide again, G1 is followed by replication of the DNA, during the S phase. The S phase (synthesis phase) is period during which a cell replicates its DNA.

After the synthesis phase, the cell proceeds through the G2 phase. The G2 phase is a second gap phase, during which the cell continues to grow and makes the necessary preparations for mitosis. Between G1, S, and G2 phases, cells will vary the most in their duration of the G1 phase. It is here that a cell might spend a couple of hours, or many days. The S phase typically lasts between 8-10 hours and the G2 phase approximately 5 hours. In contrast to these phases, the G0 phase is a resting phase of the cell cycle. Cells that have temporarily stopped dividing and are resting (a common condition) and cells that have permanently ceased dividing (like nerve cells) are said to be in G0.

B. The Structure of Chromosomes

Billions of cells in the human body divide every day. During the synthesis phase (S, for DNA synthesis) of interphase, the amount of DNA within the cell precisely doubles. Therefore, after DNA replication but before cell division, each cell actually contains two copies of each chromosome. Each copy of the chromosome is referred to as a sister chromatid and is physically bound to the other copy.(Note that the term “sister chromatid” is used regardless of the sex of the person.) The centromere is the structure that attaches one sister chromatid to another. Because a human cell has 46 chromosomes, during this phase, there are 92 chromatids (46 × 2) in the cell. Make sure not to confuse the concept of a pair of chromatids (one chromosome and its exact copy attached during mitosis) and a homologous pair of chromosomes (two paired chromosomes which were inherited separately, one from each parent) (Figure 2).

C. Mitosis and Cytokinesis

The mitotic phase of the cell typically takes between 1 and 2 hours. During this phase, a cell undergoes two major processes. First, it completes mitosis, during which the contents of the nucleus are equitably pulled apart and distributed between its two halves. Cytokinesis then occurs, dividing the cytoplasm and cell body into two new cells. Mitosis is divided into four major stages that take place after interphase (Figure 3) and in the following order: prophase, metaphase, anaphase, and telophase. The process is then followed by cytokinesis.

Prophase is the first phase of mitosis, during which the loosely packed chromatin coils and condenses into visible chromosomes. During prophase, each chromosome becomes visible with its identical partner attached, forming the familiar X-shape of sister chromatids. The nucleolus disappears early during this phase, and the nuclear envelope also disintegrates.

A major occurrence during prophase concerns a very important structure that contains the origin site for microtubule growth. Recall the cellular structures called centrioles that serve as origin points from which microtubules extend. These tiny structures also play a very important role during mitosis. A centrosome is a pair of centrioles together. The cell contains two centrosomes side-by-side, which begin to move apart during prophase. As the centrosomes migrate to two different sides of the cell, microtubules begin to extend from each like long fingers from two hands extending toward each other. The mitotic spindle is the structure composed of the centrosomes and their emerging microtubules.

Near the end of prophase there is an invasion of the nuclear area by microtubules from the mitotic spindle. The nuclear membrane has disintegrated, and the microtubules attach themselves to the centromeres that adjoin pairs of sister chromatids. The kinetochore is a protein structure on the centromere that is the point of attachment between the mitotic spindle and the sister chromatids. This stage is referred to as late prophase or “prometaphase” to indicate the transition between prophase and metaphase.

Metaphase is the second stage of mitosis. During this stage, the sister chromatids, with their attached microtubules, line up along a linear plane in the middle of the cell. A metaphase plate forms between the centrosomes that are now located at either end of the cell. The metaphase plate is the name for the plane through the center of the spindle on which the sister chromatids are positioned. The microtubules are now poised to pull apart the sister chromatids and bring one from each pair to each side of the cell.

Anaphase is the third stage of mitosis. Anaphase takes place over a few minutes, when the pairs of sister chromatids are separated from one another, forming individual chromosomes once again. These chromosomes are pulled to opposite ends of the cell by their kinetochores, as the microtubules shorten. Each end of the cell receives one partner from each pair of sister chromatids, ensuring that the two new daughter cells will contain identical genetic material.

Telophase is the final stage of mitosis. Telophase is characterized by the formation of two new daughter nuclei at either end of the dividing cell. These newly formed nuclei surround the genetic material, which uncoils such that the chromosomes return to loosely packed chromatin. Nucleoli also reappear within the new nuclei, and the mitotic spindle breaks apart, each new cell receiving its own complement of DNA, organelles, membranes, and centrioles. At this point, the cell is already beginning to split in half as cytokinesis begins.

The cleavage furrow is a contractile band made up of microfilaments that forms around the midline of the cell during cytokinesis. (Recall that microfilaments consist of actin.) This contractile band squeezes the two cells apart until they finally separate. Two new cells are now formed. One of these cells (the “stem cell”) enters its own cell cycle; able to grow and divide again at some future time. The other cell transforms into the functional cell of the tissue, typically replacing an “old” cell there.

Imagine a cell that completed mitosis but never underwent cytokinesis. In some cases, a cell may divide its genetic material and grow in size, but fail to undergo cytokinesis. This results in larger cells with more than one nucleus. Usually this is an unwanted aberration and can be a sign of cancerous cells.
A very elaborate and precise system of regulation controls direct the way cells proceed from one phase to the next in the cell cycle and begin mitosis. The control system involves molecules within the cell as well as external triggers. These internal and external control triggers provide “stop” and “advance” signals for the cell. Precise regulation of the cell cycle is critical for maintaining the health of an organism, and loss of cell cycle control can lead to cancer.

A. Mechanisms of Cell Cycle Control

As the cell proceeds through its cycle, each phase involves certain processes that must be completed before the cell should advance to the next phase. A checkpoint is a point in the cell cycle at which the cycle can be signaled to move forward or stopped. At each of these checkpoints, different varieties of molecules provide the stop or go signals, depending on certain conditions within the cell. A cyclin is one of the primary classes of cell cycle control molecules (Figure 4). A cyclin-dependent kinase (CDK) is one of a group of molecules that work together with cyclins to determine progression past cell checkpoints. By interacting with many additional molecules, these triggers push the cell cycle forward unless prevented from doing so by “stop” signals, if for some reason the cell is not ready. At the G1 checkpoint, the cell must be ready for DNA synthesis to occur. At the G2 checkpoint the cell must be fully prepared for mitosis. Even during mitosis, a crucial stop and go checkpoint in metaphase ensures that the cell is fully prepared to complete cell division. The metaphase checkpoint ensures that all sister chromatids are properly attached to their respective microtubules and lined up at the metaphase plate before the signal is given to separate them during anaphase.

B. The Cell Cycle Out of Control: Implications

Most people understand that cancer or tumors are caused by abnormal cells that multiply continuously. If the abnormal cells continue to divide unstopped, they can damage the tissues around them, spread to other parts of the body, and eventually result in death. In healthy cells, the tight regulation mechanisms of the cell cycle prevent this from happening, while failures of cell cycle control can cause unwanted and excessive cell division. Failures of control may be caused by inherited genetic abnormalities that compromise the function of certain “stop” and “go” signals. Environmental insult that damages DNA can also cause dysfunction in those signals. Often, a combination of both genetic predisposition and environmental factors lead to cancer.

The process of a cell escaping its normal control system and becoming cancerous may actually happen throughout the body quite frequently. Fortunately, certain cells of the immune system are capable of recognizing cells that have become cancerous and destroying them. However, in certain cases the cancerous cells remain undetected and continue to proliferate. If the resulting tumor does not pose a threat to surrounding tissues, it is said to be benign and can usually be easily removed. If capable of damage, the tumor is considered malignant and the patient is diagnosed with cancer.

OpenStax. (2022). Anatomy and Physiology 2e. Rice University. Retrieved June 15, 2023. ISBN-13: 978-1-711494-06-7 (Hardcover) ISBN-13: 978-1-711494-05-0 (Paperback) ISBN-13: 978-1-951693-42-8 (Digital). License: Attribution 4.0 International (CC BY 4.0). Access for free at openstax.org.

The two major phases of the cell cycle include mitosis (designated M), when the cell divides, and interphase, when the cell grows and performs all of its normal functions. Interphase is further subdivided into G1, S, and G2 phases.

The red and blue colors correspond to a homologous pair of chromosomes. Each member of the pair was separately inherited from one parent. Each chromosome in the homologous pair is also bound to an identical sister chromatid, which is produced by DNA replication, and results in the familiar “X” shape.

The stages of cell division oversee the separation of identical genetic material into two new nuclei, followed by the division of the cytoplasm.

Cells proceed through the cell cycle under the control of a variety of molecules, such as cyclins and cyclin-dependent kinases. These control molecules determine whether or not the cell is prepared to move into the following stage.

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Xem video và cảm nhận nội dung bài. Bạn có thể thả trôi, cảm nhận dòng chảy ngôn ngữ và không nhất thiết phải hiểu toàn bộ bài. Bên dưới là script để bạn khái quát nội dụng và tra từ mới.
Script:
  1. The life of cell consists of stages that make up the cell cycle.
  2. After a cell is born, it passes through an interphase before it is ready to replicate itself and produce daughter cells.
  3. This interphase includes two gap phases (G1 and G2), as well as an S phase.
  4. During which its DNA is replicated in preparation for cell division.
  5. The cell cycle is under precise regulation by chemical messengers both inside and outside the cell that provide “stop” and “go” signals for movement from one phase to the next.
  6. Failures of these signals can result in cells that continue to divide uncontrollably, which can lead to cancer.
  7. Once a cell has completed interphase and is ready for cell division, it proceeds through four separate stages of mitosis.
  8. They are prophase, metaphase, anaphase, and telophase.
  9. Telophase is followed by the division of the cytoplasm, which generates two daughter cells.
  10. This process takes place in all normally dividing cells of the body except for the germ cells that produce eggs and sperm.
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