Chapter 8 viruses
Bạn đang xem bản rút gọn của tài liệu. Xem và tải ngay bản đầy đủ của tài liệu tại đây (869.2 KB, 18 trang )
Viruses
Higher Human Biology
Lesson Aims
•
To describe the structure of a virus
•
To examine the process of viral replication
Different types of viruses
•
Influenza virus
•
AIDS virus
Different Shaped Viruses
Size
•
Smaller than bacteria
•
20-300 nanometres
(nm)
Structure of a Virus
•
A virus contains
nucleic acid (DNA or
RNA)
•
Surrounded by a
protective coat
(capsid)
Entering the Host Cell
•
Different viruses employ different methods
of entering the host cell
•
Process depends on antigenic sites on the
virus binding with certain complementary
molecules in the membrane or the specific
host cell
•
Following binding the nucleic acid is
introduced into the host cell
Binding With the Host Cell
Assembly of New Viruses
•
Once in the host cell the virus assumes
control of the cell’s biochemical machinery
•
Host cell supplies energy (ATP),
nucleotides, amino acids
•
Host then makes many identical copies of
viral nucleic acid and protein coats
Release
•
Either by LYSIS (bursting of the host cell
membrane)
•
Or BUDDING (the cell membrane pinches
off containing the new viral particle)
Before and After Lysis
Budding
Smallpox
Retrovirus
•
A retrovirus contains
RNA
•
It also contains reverse
transcriptase an
enzyme which
produces viral DNA
from viral RNA
•
The virus can thus
replicate itself
Acquired Immune Deficiency
Syndrome (AIDS)
•
AIDS is a retrovirus
•
It attacks helper T-
lymphocytes
•
The AIDS virus
attaches itself by
glycoprotein on its
surface to receptors on
the helper T cell
surface
AIDS
•
The envelope surrounding the HIV particle fuses
with the membrane of the helper T-cell and the
virus enters the host cell
•
Viral DNA becomes incorporated into the host
cell’s DNA where it can remain dormant for many
years
•
Viral mRNA is transcribed and it directs synthesis
of new viral particles inside the host cells
•
These escape from the infected helper T cell by
budding.
•
The original T cell’s membrane is left perforated
which causes destruction of the cell
The Facts You Need To Know
•
page 5
•
from “a virus can only be seen….”
•
to “e.g. the viral nucleic acid…”
