Name: how viruses infect cells and multiply
Uploaded: 2019-03-11T09:21:23.000Z
Duration: 50 s
Channel: JoVE

K12 Standards

Louisiana Student Standards for Science

High School

Life Sciences

from-molecules-to-organisms-structures-and-processes

From Molecules To Organisms: Structures And Processes

HS-LS1-8

What are Viruses?

נגיף הוא מבנה אשר נושא חומר גנטי משלו בצורת רנ"א או דנ"א, כדי לפלוש ולהשתכפל בתוך התא המארח. לאחר שנגיף נקשר לקולטנים שעל פני שטח התא המארח, הוא נכנס פנימה‫ומתפרק במהירות, ובכך חושף את החומר הגנטי שלו. במקרה של נגיפי דנ"א, הדנ"א הוויראלי מכוון את חלבוני השכפול בתא מארח לסנתז עותקים חדשים של הגנום הוויראלי.שבתורם משועתקים ומתורגמים לחלבונים ויראליים. לבסוף, המארח מרכיב מחדש רכיבים ויראליים אלו לצאצא, ובכך מאפשר לחלקיק נגיפי בודד לייצר עוד אלפים דומים, מה שלרוב מסתיים במות התא המארח.

ימאוצ'י, יוהיי וארי הלניוס. "כניסת וירוס במבט חטוף." J Cell Sci 126, no. 6 (מרץ 15, 2013): 1289-95. [<a href="https://doi.org/10.1242/jcs.119685" target="__blank">מקור</a>]

לין, דרק מ, בריט קוסקלה והנרי סי לין. "טיפול בפאגים: חלופה לאנטיביוטיקה בעידן של עמידות לתרופות מרובות". כתב העת העולמי לפרמקולוגיה וטיפולים במערכת העיכול 8, מס '3 (6 באוגוסט 2017): 162–73. [<a href="https://doi.org/10.4292/wjgpt.v8.i3.162" target="__blank">מקור</a>]

ניקז, ואלרי. "חסינות יבולים מפני וירוסים: תוצאות ואתגרים עתידיים." Frontiers in Plant Science 5 (21 בנובמבר 2014). [<a href="https://doi.org/10.3389/fpls.2014.00660" target="__blank">מקור</a>]

מה הם וירוסים?

<div style="direction:rtl"><h4>סקירה כללית</h4> נגיף הוא חלקיק זיהומי מיקרוסקופי המורכב מגנום RNA או DNA סגור במעטפת חלבון. הוא אינו מסוגל להתרבות בעצמו: הוא יכול ליצור יותר וירוסים רק על ידי כניסה לתא ושימוש במכונות הסלולריות שלו. כאשר וירוס מדביק תא מארח, הוא מסיר את מעטפת החלבון שלו ומנחה את המנגנון של המארח לשעתק ולתרגם את החומר הגנטי שלו. התא החטוף מרכיב את הרכיבים המשוכפלים לאלפי צאצאים ויראליים, שעלולים להיקרע ולהרוג את התא המארח. הנגיפים החדשים ממשיכים להדביק עוד תאים מארח. <h4>למה ללמוד וירוסים?</h4> וירוסים יכולים להדביק סוגים שונים של תאים: חיידקים, צמחים ובעלי חיים. וירוסים המכוונים לחיידקים, הנקראים בקטריופאגים (או פאג'ים), נמצאים בשפע מאוד. המחקר הנוכחי מתמקד בטיפול בפאג'ים לטיפול בזיהומים חיידקיים עמידים לריבוי תרופות בבני אדם. גם וירוסים שמדביקים צמחים תרבותיים נחקרים מאוד מאחר שמגיפות מובילות ליבול עצום ולהפסדים כלכליים. וירוסים התגלו לראשונה במאה ה-19 כאשר יבול בעל חשיבות כלכלית, צמח הטבק, היה מוכה במחלה מסתורית וזוהה מאוחר יותר כנגיף מוזאיקת הטבק. לנגיפים של בעלי חיים חשיבות רבה הן במחקר הווטרינרי והן במחקר הרפואי. יתרה מכך, וירוסים עומדים בבסיס מחלות אנושיות רבות, החל מהצטננות, אבעבועות רוח והרפס, ועד לזיהומים מסוכנים יותר כמו קדחת צהובה, הפטיטיס ואבעבועות שחורות. <h4>המבנה של וירוס</h4> וירוסים מגיעים במגוון צורות המתמחים בתקיפת תא המטרה שלהם. שני המרכיבים העיקריים של כל הנגיפים הם הגנום הנגיפי ומעיל החלבון המגן שלו, המכונה קפסיד. הגנום הנגיפי מורכב מ-RNA או DNA חד-גדילי או דו-גדילי, והוא מקודד את החלבונים המרכיבים את הקפסיד. יחד, הגנום הנגיפי והקפסיד ידועים כנוקלאוקפסיד. תכונה ייחודית של נגיפים אוקריוטיים רבים היא נוכחות של קרום פוספוליפיד, המכונה המעטפת המקיפה את הקפסיד. מעטפה זו מקורה בדרך כלל ממברנות של תאי מארח שנדבקו בעבר, אך יכולה לכלול גם חלבונים ויראליים (הנקראים חלבוני מעטפת) המחוברים אליה. לבסוף, לחלק מהנגיפים של בעלי חיים יש מקבץ של חלבונים מקודדים לווירוס, הטגומנט הנגיפי, ברווח שבין המעטפה לקפסיד. <h4>זיהום ויראלי</h4> ניתן לחלק את מחזור החיים הוויראלי לחמשת השלבים הבאים: היקשרות, חדירה, שכפול, הרכבה ושחרור. החלבונים על פני הנגיף עוזרים לו לזהות תאים מארח ספציפיים. נגיפים מסוימים משתמשים בחלבוני פני השטח הללו כדי לקשור את הקולטנים של התא המארח ולהתחיל הפנמה על ידי אנדוציטוזיה, בעוד וירוסים מצופים במעטפה יכולים להתמזג ישירות עם קרום התא המארח. חלק מהבקטריופאג'ים אינם נכנסים לתא; הם מחדירים את הגנום שלהם (ואנזימים ויראליים) לתא המארח. ברגע שנכנס לתא, הנגיף אינו מצופה ומכוון את המנגנון של התא המארח לשעתק ולתרגם את הגנום שלו. התא המארח אורז את העותקים החדשים של הגנום הנגיפי לחלקיקים ויראליים כדי ליצור צאצאים. ניתן לאחסן את וירוסי הצאצאים בתא המארח לפני השחרור או להישלף ללא הרף מהתא על ידי ניצנים מקרום התא. מחזור הזיהום הנגיפי מסווג כליטי או ליזוגני. במחזור הליטי, הנגיפים החדשים פורצים מהתא המארח ובכך הורגים אותו. במחזור הליזוגני, ה-DNA הנגיפי משולב בגנום המארח שם הוא מונח רדום ומשועתק בכל פעם שהתא המארח משתכפל.</div>

סקירה

וירוס הוא חלקיק זיהומי מיקרוסקופי המורכב מגנום RNA או DNA המוקף במעטפת חלבון. זה לא מסוגל להתרבות על ...

Education

JoVE Core

Biology

ביולוגיה

Genetics

גנטיקה

Viruses

נגיפים

KEY TERMS AND CONCEPTS

מונחים ומושגים מרכזיים

how viruses infect cells and multiply

Viruses infect cells and make new copies by using a host cell’s own machinery. A virus is a tiny infectious particle with an RNA or DNA genome inside a protective protein coat. It cannot reproduce on its own, so it must enter a cell to make more viruses.

After infection, the virus sheds its protein coat and uses the host cell to transcribe and translate its genetic material. The cell then assembles many new viral particles. In many cases, these new viruses rupture the host cell and kill it. The released viruses can then infect other cells.

Viruses can attack bacteria, plants, and animals. Viruses that infect bacteria are called bacteriophages, or phages, and they are very abundant. Scientists also study phages as a possible therapy for multidrug-resistant bacterial infections in humans. Plant viruses matter because outbreaks can cause major crop and economic losses.

Animal viruses are important in both veterinary research and medical research. Viruses were first discovered in the 19th century during studies of tobacco plants with a mysterious disease. That disease was later identified as Tobacco mosaic virus. Viruses are also linked to many human illnesses, including the common cold, chickenpox, herpes, yellow fever, hepatitis, and smallpox.

Viruses vary in shape, but they share two main parts: the viral genome and the capsid. The genome can be single-stranded or double-stranded RNA or DNA, and it carries the instructions for making capsid proteins. The genome and capsid together form the nucleocapsid. Many eukaryotic viruses also have an envelope, which is a phospholipid membrane often taken from a host cell. Some animal viruses also contain a tegument, a layer of viral proteins between the envelope and the capsid.

A viral infection usually follows five stages: attachment, entry, replication, assembly, and release. Viral surface proteins help the virus recognize the right host cell. Some viruses bind to host receptors and enter by endocytosis, while enveloped viruses can fuse with the host cell membrane. Some bacteriophages do not enter the cell at all. They inject their genome and viral enzymes into the host cell instead.

Once inside, the virus is uncoated and directs the host cell to copy and read its genetic material. The host cell packages the new genomes into viral particles to form progeny viruses. These progeny may stay in the cell for a time or leave by budding from the cell membrane. Viral infection can be lytic or lysogenic. In the lytic cycle, new viruses burst out and kill the host cell. In the lysogenic cycle, viral DNA becomes part of the host genome, stays dormant, and is copied when the host cell divides.

How Viruses Infect Cells and Multiply

what are viruses?

Viruses infect cells and make new copies by using a host cell’s own machinery. A virus is a tiny infectious particle with an RNA or DNA genome inside a protective protein coat. It cannot reproduce on its own, so it must enter a cell to make more viruses. After infection, the virus sheds its protein coat and uses the host cell to transcribe and translate its genetic material. The cell then assembles many new viral particles. In many cases, these new viruses rupture the host cell and kill it.

viral structure

How Virus Shapes Help Infection

Viruses have specific structures that help them infect host cells and trigger immune responses. Each virus has a core that contains either a DNA-based or RNA-based genome. That core is surrounded by a protective protein coat called the capsid. The capsid is made of smaller subunits called capsomeres. The capsid and the genome-containing core together are called the nucleocapsid. Viruses are often grouped by capsid design. Most viruses have either icosahedral or helical capsids, but some have...

lytic cycle of bacteriophages

How Phages Infect and Burst Bacteria

Bacteriophages, or phages, are viruses that infect bacteria. They have a distinctive head-tail shape. In the lytic cycle, a phage first attaches to the outside of a bacterial cell. Tail proteins bind to specific receptor proteins on the bacterium’s surface. After attachment, the phage tail injects its DNA genome into the bacterial cytoplasm. The phage then uses the bacterium’s cellular machinery to make proteins needed for replication and dispersal. When phage replication is complete, some of...

lysogenic cycle of bacteriophages

Prophage Integration in Bacteria

The lysogenic cycle shows how bacteriophages can infect bacteria without killing the host right away. In this cycle, the phage genome joins the bacterial genome. The integrated phage DNA is called a prophage, and the bacterium copies it each time it replicates. Some prophages can switch back into the lytic cycle. This change can happen after DNA damage or even without an obvious outside trigger. When the prophage is induced, the phage begins making new virus particles again. Prophages can...

retrovirus life cycles

How Retroviruses Replicate in Host Cells

Retroviruses replicate by copying their RNA genome into DNA inside a host cell. After entry, the viral enzyme reverse transcriptase makes a double-stranded DNA copy from the single-stranded RNA genome. The viral DNA is then carried into the nucleus and inserted into the host genome by integrase. Once integrated, the retroviral DNA is transcribed whenever the host genome is transcribed. This produces new viral RNA that can be copied and used again. The new RNA moves into the cytoplasm, where it...

viral recombination

How Viruses Swap Genes and Spread

Viral gene swapping can happen when more than one virus infects the same cell. After the viruses break open and expose their genomes for replication, matching regions can pair up and exchange sequences. This process is called recombination. Viruses with segmented genomes can also swap whole segments, which is called reassortment. These changes can help create new diseases. Some diseases can infect more than one species. Pigs can be infected by some human and bird viruses, along with the...

viral mutations

How Virus Mutations Drive Outbreaks

Virus mutations can change how quickly a virus evolves and spreads. A mutation is a change in the sequence of bases in DNA or RNA. Some mutations happen when the genome is copied. They are caused by errors made by polymerase enzymes, which replicate DNA or RNA. RNA viruses often change faster than DNA viruses because RNA polymerase does not proofread its work. That means RNA-based genomes, such as HIV, can gather mutations more quickly. Mutation and recombination give viruses the raw material...

key terms and concepts

Learn how viruses enter host cells, use cellular machinery to replicate, and spread through lytic and lysogenic cycles in plants, animals, and bacteria.

How Viruses Infect Cells and Multiply | JoVE K12

JoVE Core series brings biology to life through over 300 concise and easy-to-understand animated video lessons that explain key concepts in biology, plus more than 150 scientist-in-action videos that show actual research experiments conducted in today’s laboratories.

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Nucleic Acids and Nucleotides

Nucleic acids are the most important macromolecules for the continuity of life. They carry the cell&#39;s genetic blueprint and have instructions for its ...

Nucleic Acid Structure

The pentose sugar in DNA is deoxyribose, while in RNA the pentose sugar is ribose. The difference between the sugars is the presence of the hydroxyl group ...

DNA Base Pairing

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The central dogma explains the flow of genetic information from DNA nucleotides to the amino acid sequence of proteins.
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Overview

Deoxyribonucleic acid, or DNA, is the genetic material responsible for passing traits from generation to generation in all organisms and most ...

DNA Packaging

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Eukaryotes have large genomes compared to prokaryotes. In order to fit their genomes into a cell, eukaryotes must pack their DNA tightly inside ...

RNA Structure

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RNA Stability

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pre-mRNA Processing

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Types of RNA

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DNA as a Genetic Template

What is Gene Expression?

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Transcription

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Translation

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structure-and-organization-of-smooth-muscles

Structure and Organization of Smooth Muscles

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...

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Heterochromatin

Lymphoid Cells and Tissues

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chromatin-position-affects-gene-expression

Chromatin Position Affects Gene Expression

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Organization of Genes

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Construct an explanation based on evidence for how the structure of DNA determines the structure of proteins which carry out the essential functions of life through systems of specialized cells. Emphasis is on the conceptual understanding that DNA sequences determine the amino acid sequence and thus protein structure. Students can produce scientific writing, or presentations, and/or physical models that communicate constructed explanations.

HS-LS1-1

Characteristics of Life

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HS-LS1-2

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Positive and Negative Feedback Loops

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Negative and Positive Feedback

Homeostatic Imbalance

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pH Homeostasis

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homeostatic-imbalances-in-body-temperature

Homeostatic Imbalances in Body Temperature

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...

Regulation of Food Intake

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Plan and conduct an investigation to provide evidence that feedback mechanisms maintain homeostasis in living organisms. Examples of investigations could include heart rate responses to exercise, stomate responses to moisture and temperature, root development in response to water levels, or cell response to hypertonic and hypotonic environments.

HS-LS1-3

What is the Cell Cycle?

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Interphase

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The Cell Cycle Control System

Positive Regulator Molecules

Inhibition of CDK Activity

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M-Cdk Drives Transition Into Mitosis

Mitogens and the Cell Cycle

Replicative Cell Senescence

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cells-coordinate-growth-and-proliferation

Cells Coordinate Growth and Proliferation

Mitosis and Cytokinesis

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Chromosome Duplication

Cohesins

Condensins

The Mitotic Spindle

Centrosome Duplication

Spindle Assembly

Attachment of Sister Chromatids

Forces Acting on Chromosomes

Separation of Sister Chromatids

Use a model to illustrate the role of the cell cycle and differentiation in producing and maintaining complex organisms. Emphasis is on conceptual understanding that mitosis passes on genetically identical materials via replication, not on the details of each phase in mitosis.

HS-LS1-4

How Viruses Infect Cells and Multiply

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