Essay On Biology Questions

- Describe the phases of meiosis II
Meiosis II has 4 phases, prophase, metaphase, anaphase, and telophase. At the end of meiosis I, microtubules move each member of the centriole pair to an opposite spindle pole in both daughter cells. During prophase II, the microtubules attach to the chromosomes causing them to recoil and shorten. During metaphase II, the microtubules, duplicated chromosomes, and motor proteins, interact in a manner that positions all the duplicated chromosomes halfway between the 2 spindle poles. During anaphase II, the connection between the 2 sister chromatids of every chromosome breaks and each of the chromatids is moved to an opposite spindle pole. Every sister chromatid then becomes a chromosome of its own. During telophase II, the chromosomes uncoil and nuclear envelops are reformed. The process culminates with the formation of 4 daughter cells with haploid (n) chromosomes.
- What are the phases of mitosis and summarize the highlights of each phase.
Mitosis is a continuous process although it is usually divided into 4 stages: prophase, metaphase, anaphase, and telophase. During prophase, chromosome strands begin to coil, shorten, and thicken, the nuclear membrane starts to disappear, and spindle apparatus form in the cell’s cytoskeleton. Some of the chromosomes become attached to these fibers. During the second stage, metaphase, the chromosome move and align themselves at the center of the cell perpendicular to the spindle fibers. The chromosome strands separate as anaphase begins. The spindle fibers shorten and start moving every replicated chromosome towards opposite poles of the dividing cell. During telophase, the chromosomes reach the opposite ends of the cell. New nuclear membranes form and envelop each set of chromosomes resulting in the formation of 2 nuclei. Each nucleus contains a chromosome set similar to that of the parent cell.
- Discuss sex regulation in humans. What is the determining factor in gender regulation in early embryos?
The cells of human males have 2 different sex chromosomes X and Y whilst those of females have 2 X chromosomes (XX). The sex of a new individual in humans is determined by the sex chromosomes that one inherits. The egg (ova) of a female contains 1 X chromosome. Half the sperm cells carry the X-chromosome while the other half carries the Y-chromosome. If a Y-bearing sperm fertilizes an egg, a male embryo is formed. A female embryo forms if an X-containing sperm fertilizes an ova. The Y chromosome is the gender regulating factor in early embryos. It enhances the growth of the undifferentiated gonads and subsequent development into testes.
- Describe Transcription OR Translation. Include definition, molecules involved and process. Be specific and complete.
Transcription is the process via which information contained in the DNA of a gene is replicated into a functional blueprint made of RNA. This blueprint is later used as a template in the formation of the polypeptide chains of proteins. The transcription process has 4 components: promoter recognition, initiation, elongation, and termination. The process begins with the identification of a gene sequence usually 20-200 bases long called the promoter by the enzyme RNA polymerase. It is usually located upstream (5’) of the transcription initiation site. The binding of the polymerase to the promoter causes the DNA to open and separate into 2 separate strands so as to facilitate access to the single strand that is used as a template. Transcription begins at a specific site identified as +1. It starts with the binding of a complementary ribonucleotide to the DNA nucleotides at the start site. The enzyme, RNA polymerase, then moves along the transcript DNA strand adding more complementary ribonucleotides to the elongating RNA strand in a 5’ to 3’ orientation. The process terminates when the enzyme reaches a precoded termination sequence. The polymerase separates from the template strand. The single-stranded RNA template also called mRNA is then released and the separated DNA strands rebind. The mRNA then undergoes post-transcriptional processing whereby it is capped with 7-methly-guanosine cap at its 5’ end and adenosine nucleotides are added to its 3’ end. It then undergoes RNA splicing in the spliceisome of the nucleus. Splicing entails removal of introns. The remaining sequences are then ligated to form exons, the mRNA transcript that undergoes translation.