MDCAT Biology Entry Test Preparation Acellular Life Key Points. Key Concepts of Acellular Life Preparation for the MDCAT Biology Entry Test. Important Biology mdcat cramming points. Acellular life unit evaluations and revisions for the MDCAT in biology.
Key Concepts of Acellular Life
In order to help you prepare for the MDCAT Biology admission test, we’ve compiled some key concepts and study materials for acellular life. The following is a list of the important talking points.
- A virus is an extremely tiny parasite that can only reproduce if it is within a living being.
- Viruses can infect all types of lifeforms, from animals and plants to
microorganisms, including bacteria and archaea.
- Viruses lie on the borderline between living things and nonliving things.
- Viruses are considered as living because viruses possess DNA or RNA.
- Viruses have the ability to reproduce, can also undergo mutation and genetic recombination.
- Among nonliving characters, viruses are subcellular or noncellular structures.
- They do not respire or excrete, can be crystallized and stored in much the
same way as chemicals.
- Viruses can be broadly classified based on morphology and the type of host they infect.
- On the basis of morphology, there are 3 classes of viruses; Le. spherical virus (polio virus), tadpole-shaped virus (bacteriophage), and rod-shaped virus (tobacco mosaic virus).
10.On the basis of the host, viruses are;
11.Animal like viruses are the parasites of animals and human beings and causes diseases in them.
12.Common diseases in man are polio, smallpox, measles, mumps, and influenza, etc.
13.Plants viruses are parasites of plants and cause diseases in them.
14.Bacteriophage (phage) is a parasite only on bacteria.
15.Bacteriophage are obligate intracellular parasites that multiply inside bacteria by making use of host biosynthetic machinery.
16.Size of phage ranges from 24-200 nm in length.
17.All phages contain head (capsid) structures that can vary in size and shape i.e some are icosahedral (20 sides) others are filamentous.
- Tail of phage is a hollow tube through which nucleic acid passes during an infection- do not even have a tail ‘”
- The size of the tail can vary and some phage
structure. late and one or more t 1
21.In more complex phages like T4 have a base P, at
fibers attached to it, which are involved in the attachment Of phage to the bacterial cell.
22.Not all phages have base plates and tail fibers, m these instances other structures are involved in the attachment of the phage particle to the. bacterium
23.H/V particle is around100-150 billionths o a meter in diameter i.e about the same as 0.1 microns, 4 millionths of an inch, one-twentieth o the length of an Ecoli bacterium, one-seventieth of the diameter of a human CD4 WBC.
24.H/Vhas 72 little spikes which are formed from the proteins gp120 and
25: below the viral envelope is a layer called the matrix which is made from the protein.p17.
- Viral core or capsid is usually bullet-shaped and is usually made from protein p24.
27.Inside the core ore 3 enzymes required for H/V replication called reverse transcriptase, integrase, and protease.
28.H/V genetic material consists of two identical strands of RNA.
29.HIV belongs to a special class of viruses called retroviruses in which HIV is placed in the subgroup of lentiviruses.
31.HIV has just 9 genes, three of its genes called gag, pol, and envy contain information needed to make structural proteins for new virus particles.
33.Bacterium has more than 500 genes.
34.Human has around 20000-25000 genes.
35 Influenza is an RNA virus that may exist in different shapes from round
balls to long, spaghetti-like filaments.
- The genome of this virus is associated with five different viral proteins and is surrounded by a lipid membrane, which means that influenza belongs to the enveloped group of viruses.
37.Eight separate pieces of RNA make up the influenza virus genome and each piece of RNA specifies the amino acid sequence of one and sometimes two of the virus’s proteins.
- Two glycoprotein molecules, known as hemagglutinin (HA) and neuraminidase Ina) are stuck onto the lipid envelope of the virus and both play a crucial role in the infection of the epithelial cells of the upper respiratory tract.
39.HA is a rod-shaped triangular molecule and NA exists as a mushroom-shaped spike with a box-like head on top of a long stalk, containing a hydrophobic region by which it is embedded in the viral membrane.
- There are many strains of the phage but only one kind of phage will attack only one strain or one species of bacteria.
- There are two types of the life cycle of phage namely the lytic cycle and the Lysogenic cycle.
42./n lytic cycle the phage is regarded as virulent or master and the bacterial cell (host) is regarded as a slave.
43.ln lytic cycle the phage first attaches itself by its tail to the cell wall of the bacterium at a point called receptor site.
- The phage contains an enzyme called lysozyme which digests the cell wall of the bacterium. Thus an opening is formed in the bacterial cell wall.
- The phage injects its DNA inside the host while the protein coat and the tail remain outside.
46./nside the bacterial cell, the phage DNA takes over the biosynthetic machinery of the host to synthesize its own DNA and protein molecule.
- The phage divides and increases in number. The daughter phages exert pressure on the cell wall of the bacterium.
- Thus the bacterial cell ruptures and releases the daughter phages, which are now ready to attack new bacterium and start their own cycle again.
- In the lysogenic cycle, the phage does not kill or destroy the bacterium (host).
50.In this case the phage becomes a harmless guest and the bacterium acts as a host.
51.ln cycle when the phage DNA enters the bacterial cell, instead of taking
over the control of No synthetic machinery of the host, it becomes associated and mixed up with the bacterial chromosome in a friendly atmosphere.
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