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Enveloped virions like HIV (human immunodeficiency virus), the causative agent in AIDS (acquired immune deficiency syndrome), consist of nucleic acid (RNA in the case of HIV) and capsid proteins surrounded by a phospholipid bilayer envelope and its associated proteins ( [link] ). Chicken pox, influenza, and mumps are examples of diseases caused by viruses with envelopes. Because of the fragility of the envelope, nonenveloped viruses are more resistant to changes in temperature, pH, and some disinfectants than enveloped viruses.

Overall, the shape of the virion and the presence or absence of an envelope tells us little about what diseases the viruses may cause or what species they might infect, but is still a useful means to begin viral classification.

Art connection

An illustration shows bacteriophage T4, which houses its DNA genome in a hexagonal head. A long, straight tail extends from the bottom of the head. Tail fibers attached to the base of the tail are bent, like spider legs. An adenovirus houses its DNA genome in a round capsid made from many small capsomere subunits. Glycoproteins extend from the capsomere, like pins from a pincushion. The HIV retrovirus houses its RNA genome and an enzyme called reverse transcriptase in a bullet-shaped capsid. A spherical viral envelope, lined with matrix proteins, surrounds the capsid. Glycoproteins extend from the viral envelope.
Viruses can be complex in shape or relatively simple. This figure shows three relatively complex virions: the bacteriophage T4, with its DNA-containing head group and tail fibers that attach to host cells; adenovirus, which uses spikes from its capsid to bind to the host cells; and HIV, which uses glycoproteins embedded in its envelope to do so. Notice that HIV has proteins called matrix proteins, internal to the envelope, which help stabilize virion shape. HIV is a retrovirus, which means it reverse transcribes its RNA genome into DNA, which is then spliced into the host’s DNA. (credit “bacteriophage, adenovirus”: modification of work by NCBI, NIH; credit “HIV retrovirus”: modification of work by NIAID, NIH)

Which of the following statements about virus structure is true?

  1. All viruses are encased in a viral membrane.
  2. The capsomere is made up of small protein subunits called capsids.
  3. DNA is the genetic material in all viruses.
  4. Glycoproteins help the virus attach to the host cell.

Unlike all living organisms that use DNA as their genetic material, viruses may use either DNA or RNA as theirs. The virus core contains the genome or total genetic content of the virus. Viral genomes tend to be small compared to bacteria or eukaryotes, containing only those genes that code for proteins the virus cannot get from the host cell. This genetic material may be single-stranded or double-stranded. It may also be linear or circular. While most viruses contain a single segment of nucleic acid, others have genomes that consist of several segments.

DNA viruses have a DNA core. The viral DNA directs the host cell’s replication proteins to synthesize new copies of the viral genome and to transcribe and translate that genome into viral proteins. DNA viruses cause human diseases such as chickenpox, hepatitis B, and some venereal diseases like herpes and genital warts.

RNA viruses contain only RNA in their cores. To replicate their genomes in the host cell, the genomes of RNA viruses encode enzymes not found in host cells. RNA polymerase enzymes are not as stable as DNA polymerases and often make mistakes during transcription. For this reason, mutations, changes in the nucleotide sequence, in RNA viruses occur more frequently than in DNA viruses. This leads to more rapid evolution and change in RNA viruses. For example, the fact that influenza is an RNA virus is one reason a new flu vaccine is needed every year. Human diseases caused by RNA viruses include hepatitis C, measles, and rabies.

Questions & Answers

why are the laws of thermodynamics considered laws of nature and not scientific theories
Yolonda Reply
archea were given their own separate domain because they are?
which of the following is a basic component of all of the others?
which of the following organization levels is the least inclusive
which cell feature is absent in bacterial cells
which metric movies the base unit of measurement by one thousandth (0.001)?
What is biology?
Blessing Reply
List the branches of biology
List the branches of biology
List the branches of biology
List the branches of biology
must all prokaryotic cells posses a cell wall?
chris Reply
what is biology?
Cathy Reply
biology is basically the study of life
that's true
it's the study of living things
What is a celiac disease
Falase Reply
distinguish between properties and characteristics
Elee Reply
what are organelles
organelles are substances that makes up a cell
what is biology
Prevail Reply
biology is science that studies life
it's the study of living and non living things
now that we have an estimate for the diameter of the cell.what estimate can we make about the volume of the cell?
faxhood Reply
why too much insulin result in low blood sugar
Leri Reply
For example, too much exercise can cost you to lose to much weight. Too much insulin will pull to much sugar out of your systemic system into your cells.
difference between DNA and RNA
Eyitayo Reply
DNA is deoxyribonuclaic acid. Deoxy refers to a lack of oxygen. The Ribose moity is missing an OH group. I think it is missing from the second C of the ring. RNA is ribonucleic acid. DNA has our genetic code in on it. RNA is translated from DNA and carries the blue print for protein synthesis.
The OH group on RNA prevents it from being reactive. But it is very unstable though. Would you want such a power tool floating around in your body, no. And you have three types of RNA: mRNA, tRNA and rRNA. Please let me know it this helped?😄
Eric answered this question perfectly
what determines the aeration level in the soil
Shola Reply
what is homeostasis?
Sarita Reply
It means balance in a biological system.
What is biology
Don Reply
Biology z the study of life
what's biology
biology is the study of living nd none living organism
Biology is the study of life
yes Sir
what's cell biology
biology is the study of life
Biology is a science subject that deals with the study of living things and how they interact with there environment
what is asexual reproduction,?
Awoi Reply
A type of reproduction which does not involve the fusion of gametes or a change in the number of chromosomes
Reproduction without sex... In which form a single organism or cell makes a copy of itself.
Please explain the concept of mitosis and meiosis
I guess you could use it for study buddies and brushing up on what you need to
what is mitosis
Asexual reproduction?
why pepsin and trypsin released in active form?
mitosis is the type cell division in which two daughter cells have same no. of chormosomes
chromosome number remains the same in mitosis
Yrr help me.
Physical chemistry..... Koi h jo mujhe physical chem ki notes send kr ske
what is asexual reproduction
what makes golgi body in plants
Abdulkareem Reply
name the membrane of the plants
how can turners syndrome be corrected before birth
which animal survive from being preyed just because of being humble, slow, and not aggressive
Plants have golgi body's also. Plants are eukaryotic cells. And membrane bound organelles are a characteristic of eukaryotic cells. Moreover golgi body's are creatted from the ER. Also do not forget plants have plastids and animal cells do not.

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Source:  OpenStax, Concepts of biology. OpenStax CNX. Feb 29, 2016 Download for free at http://cnx.org/content/col11487/1.9
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