Answer:
Allopatric speciation occur due to various environmental factors with in the environment.
Explanation:
Speciation occur when two population become so genetically different and the can not interbred to produce fertile off spring. The allopatric speciation occur when population become sepret and diverge over time due to natural selection,genetic drift,and mutation.Genetic drift is the sudden loss of gene from a population which cause the population evolvation. Mutation is also change in the genetic makeup of an individual.Natural selection is the phenomena selected by nature and natural forces are involve to select the trait in a living organism.
1. The correct answer is: The viral envelope proteins interact with CD4 and a co-receptor on the cell membrane.
Binding and entering the host cell are the first steps of the HIV virus infection. So, these steps play a major role in determining the ability of HIV to degrade the human immune system. Binding of HIV to CD4+ T lymphocytes (express chemokine receptors CCR5 and CXCR4 called co-receptors) triggers the fusion of the viral and host cell membranes, initiating infection (viral core gets into the cytoplasm).
Attachment of the virion can be:
• Nonspecific-envelop protein of the virus (Env) binds to cell-surface heparan sulfate proteoglycans
• Specific-Env binds to integrin.
2. The correct answer is: Activation of the host cell by cytokines, growth factors, or antigens.
After the viral capsid enters the cell, single-stranded RNA genome is released from the attached viral proteins and copied it into a complementary DNA (cDNA) molecule thanks to an enzyme called reverse transcriptase. Next step is the integration of the viral DNA into the host cell's genome. This process is done by another viral enzyme called integrase. The integrated DNA is transcribed into RNA and then translated into proteins that will help the package of new viruse particles.
3. The answer is: false
Reverse transcriptase is an enzyme that catalyzes the formation of DNA from an RNA template. Since the genome of the virus (HIV) is single stranded RNA, reverse transcriptase copies it into a complementary DNA (cDNA) molecule. Thanks to this enzyme, formed cDNA can be integrated into host’s genome. Because of this proprety, antiretroviral drugs used to treat HIV infection work as reverse-transcriptase inhibitors.
Multiplica celcius por 274.15 para saber cuanto es en kelvin.
Answer:
C.
Explanation:
Human reproduction is any form of sexual reproduction that results in fertilisation by humans. It normally includes a man and a woman having sexual intercourse. During sexual intercourse, the contact between male and female reproductive systems leads to the woman's ovum being fertilised by the man's sperm.
In human fertilization, a hapoloid ovum is released that fuses with a haploid sperm and produces a single 2n diploid cell called the zygote.
Hence, the correct option is C.
Transcription<span>. </span>Transcription<span> is the </span>process<span> by which</span>DNA<span> is copied (</span>transcribed<span>) to </span>mRNA<span>, which carries the information needed for protein synthesis. </span>Transcription<span>takes place </span>in<span> two broad steps. First, pre-messenger RNA is </span>formed<span>, with the involvement of RNA polymerase enzymes.</span>
