Module 3: The Cellular Level of Organization

Lesson 5: Protein Synthesis

Tổng Hợp Protein

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Mỗi bài học (lesson) bao gồm 4 phần chính: Thuật ngữ, Luyện Đọc, Luyện Nghe, và Bàn Luận.
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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.
It was mentioned earlier that DNA provides a “blueprint” for the cell structure and physiology. This refers to the fact that DNA contains the information necessary for the cell to build one very important type of molecule: the protein. Most structural components of the cell are made up, at least in part, by proteins and virtually all the functions that a cell carries out are completed with the help of proteins. One of the most important classes of proteins is enzymes, which help speed up necessary biochemical reactions that take place inside the cell. Some of these critical biochemical reactions include building larger molecules from smaller components (such as occurs during DNA replication or synthesis of microtubules) and breaking down larger molecules into smaller components (such as when harvesting chemical energy from nutrient molecules). Whatever the cellular process may be, it is almost sure to involve proteins. Just as the cell’s genome describes its full complement of DNA, a cell’s proteome is its full complement of proteins. Protein synthesis begins with genes. A gene is a functional segment of DNA that provides the genetic information necessary to build a protein. Each particular gene provides the code necessary to construct a particular protein. Gene expression, which transforms the information coded in a gene to a final gene product, ultimately dictates the structure and function of a cell by determining which proteins are made.

The interpretation of genes works in the following way. Recall that proteins are polymers, or chains, of many amino acid building blocks. The sequence of bases in a gene (that is, its sequence of A, T, C, G nucleotides) translates to an amino acid sequence. A triplet is a section of three DNA bases in a row that codes for a specific amino acid. Similar to the way in which the three-letter code d-o-g signals the image of a dog, the three-letter DNA base code signals the use of a particular amino acid. For example, the DNA triplet CAC (cytosine, adenine, and cytosine) specifies the amino acid valine. Therefore, a gene, which is composed of multiple triplets in a unique sequence, provides the code to build an entire protein, with multiple amino acids in the proper sequence (Figure 1). The mechanism by which cells turn the DNA code into a protein product is a two-step process, with an RNA molecule as the intermediate.
DNA is housed within the nucleus, and protein synthesis takes place in the cytoplasm, thus there must be some sort of intermediate messenger that leaves the nucleus and manages protein synthesis. This intermediate messenger is messenger RNA (mRNA), a single-stranded nucleic acid that carries a copy of the genetic code for a single gene out of the nucleus and into the cytoplasm where it is used to produce proteins.

There are several different types of RNA, each having different functions in the cell. The structure of RNA is similar to DNA with a few small exceptions. For one thing, unlike DNA, most types of RNA, including mRNA, are single-stranded and contain no complementary strand. Second, the ribose sugar in RNA contains an additional oxygen atom compared with DNA. Finally, instead of the base thymine, RNA contains the base uracil. This means that adenine will always pair up with uracil during the protein synthesis process.

Gene expression begins with the process called transcription, which is the synthesis of a strand of mRNA that is complementary to the gene of interest. This process is called transcription because the mRNA is like a transcript, or copy, of the gene’s DNA code. Transcription begins in a fashion somewhat like DNA replication, in that a region of DNA unwinds and the two strands separate, however, only that small portion of the DNA will be split apart. The triplets within the gene on this section of the DNA molecule are used as the template to transcribe the complementary strand of RNA (Figure 2). A codon is a three-base sequence of mRNA, so-called because they directly encode amino acids. Like DNA replication, there are three stages to transcription: initiation, elongation, and termination.

Stage 1: Initiation. A region at the beginning of the gene called a promoter—a particular sequence of nucleotides—triggers the start of transcription.

Stage 2: Elongation. Transcription starts when RNA polymerase unwinds the DNA segment. One strand, referred to as the coding strand, becomes the template with the genes to be coded. The polymerase then aligns the correct nucleic acid (A, C, G, or U) with its complementary base on the coding strand of DNA. RNA polymerase is an enzyme that adds new nucleotides to a growing strand of RNA. This process builds a strand of mRNA.

Stage 3: Termination. At the end of the gene, a sequence of nucleotides called the terminator sequence causes the new RNA to fold up on itself. This fold causes the RNA to separate from the gene and from RNA polymerase, ending transcription.

Before the mRNA molecule leaves the nucleus and proceeds to protein synthesis, it is modified in a number of ways. For this reason, it is often called a pre-mRNA at this stage. For example, your DNA, and thus complementary mRNA, contains long regions called non-coding regions that do not code for amino acids. Their function is still a mystery, but the process called splicing removes these non-coding regions from the pre-mRNA transcript (Figure 3). A spliceosome—a structure composed of various proteins and other molecules—attaches to the mRNA and “splices” or cuts out the non-coding regions. The removed segment of the transcript is called an intron. The remaining exons are pasted together. An exon is a segment of RNA that remains after splicing. Interestingly, some introns that are removed from mRNA are not always non-coding. When different coding regions of mRNA are spliced out, different variations of the protein will eventually result, with differences in structure and function. This process results in a much larger variety of possible proteins and protein functions. When the mRNA transcript is ready, it travels out of the nucleus and into the cytoplasm.
Like translating a book from one language into another, the codons on a strand of mRNA must be translated into the amino acid alphabet of proteins. Translation is the process of synthesizing a chain of amino acids called a polypeptide. Translation requires two major aids: first, a “translator,” the molecule that will conduct the translation, and second, a substrate on which the mRNA strand is translated into a new protein, like the translator’s “desk.” Both of these requirements are fulfilled by other types of RNA. The substrate on which translation takes place is the ribosome.

Remember that many of a cell’s ribosomes are found associated with the rough ER, and carry out the synthesis of proteins destined for the Golgi apparatus. Ribosomal RNA (rRNA) is a type of RNA that, together with proteins, composes the structure of the ribosome. Ribosomes exist in the cytoplasm as two distinct components, a small and a large subunit. When an mRNA molecule is ready to be translated, the two subunits come together and attach to the mRNA. The ribosome provides a substrate for translation, bringing together and aligning the mRNA molecule with the molecular “translators” that must decipher its code.

The other major requirement for protein synthesis is the translator molecules that physically “read” the mRNA codons. Transfer RNA (tRNA) is a type of RNA that ferries the appropriate corresponding amino acids to the ribosome, and attaches each new amino acid to the last, building the polypeptide chain one-by-one. Thus tRNA transfers specific amino acids from the cytoplasm to a growing polypeptide. The tRNA molecules must be able to recognize the codons on mRNA and match them with the correct amino acid. The tRNA is modified for this function. On one end of its structure is a binding site for a specific amino acid. On the other end is a base sequence that matches the codon specifying its particular amino acid. This sequence of three bases on the tRNA molecule is called an anticodon. For example, a tRNA responsible for shuttling the amino acid glycine contains a binding site for glycine on one end. On the other end it contains an anticodon that complements the glycine codon (GGA is a codon for glycine, and so the tRNAs anticodon would read CCU). Equipped with its particular cargo and matching anticodon, a tRNA molecule can read its recognized mRNA codon and bring the corresponding amino acid to the growing chain (Figure 4).

Much like the processes of DNA replication and transcription, translation consists of three main stages: initiation, elongation, and termination. Initiation takes place with the binding of a ribosome to an mRNA transcript. The elongation stage involves the recognition of a tRNA anticodon with the next mRNA codon in the sequence. Once the anticodon and codon sequences are bound (remember, they are complementary base pairs), the tRNA presents its amino acid cargo and the growing polypeptide strand is attached to this next amino acid. This attachment takes place with the assistance of various enzymes and requires energy. The tRNA molecule then releases the mRNA strand, the mRNA strand shifts one codon over in the ribosome, and the next appropriate tRNA arrives with its matching anticodon. This process continues until the final codon on the mRNA is reached which provides a “stop” message that signals termination of translation and triggers the release of the complete, newly synthesized protein. Thus, a gene within the DNA molecule is transcribed into mRNA, which is then translated into a protein product (Figure 5).

Commonly, an mRNA transcription will be translated simultaneously by several adjacent ribosomes. This increases the efficiency of protein synthesis. A single ribosome might translate an mRNA molecule in approximately one minute; so multiple ribosomes aboard a single transcript could produce multiple times the number of the same protein in the same minute. A polyribosome is a string of ribosomes translating a single mRNA strand.

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.

DNA holds all of the genetic information necessary to build a cell’s proteins. The nucleotide sequence of a gene is ultimately translated into an amino acid sequence of the gene’s corresponding protein.

In the first of the two stages of making protein from DNA, a gene on the DNA molecule is transcribed into a complementary mRNA molecule.

In the nucleus, a structure called a spliceosome cuts out introns (noncoding regions) within a pre-mRNA transcript and reconnects the exons.

During translation, the mRNA transcript is “read” by a functional complex consisting of the ribosome and tRNA molecules. tRNAs bring the appropriate amino acids in sequence to the growing polypeptide chain by matching their anti-codons with codons on the mRNA strand.

Transcription within the cell nucleus produces an mRNA molecule, which is modified and then sent into the cytoplasm for translation. The transcript is decoded into a protein with the help of a ribosome and tRNA molecules.

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Dưới đây là video và các luyện tập (practice) của bài này. Nghe là một kĩ năng khó, đặc biệt là khi chúng ta chưa quen nội dung và chưa có nhạy cảm ngôn ngữ. Nhưng cứ đi thật chậm và đừng bỏ cuộc.
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. DNA stores the information necessary for instructing the cell to perform all of its functions.
  2. Cells use the genetic code stored within DNA to build proteins, which ultimately determine the structure and function of the cell.
  3. This genetic code lies in the particular sequence of nucleotides that make up each gene along the DNA molecule.
  4. To “read” this code, the cell must perform two sequential steps.
  5. In the first step, transcription, the DNA code is converted into an RNA code.
  6. A molecule of messenger RNA that is complementary to a specific gene is synthesized in a process similar to DNA replication.
  7. The molecule of messenger RNA provides the code to synthesize a protein.
  8. In the process of translation, the messenger RNA attaches to a ribosome.
  9. Next, transfer RNA molecules shuttle the appropriate amino acids to the ribosome, one-by-one, coded by sequential triplet codons on the messenger RNA, until the protein is fully synthesized.
  10. When completed, the messenger RNA detaches from the ribosome, and the protein is released.
  11. Typically, multiple ribosomes attach to a single messenger RNA molecule at once such that multiple proteins can be manufactured from the messenger RNA concurrently.
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