C. Describe what happens during the segregation of homologous pairs of chromosom

Question

C. Describe what happens during the segregation of homologous pairs of chromosomes during meiosis.
Use your own words. Answer for a cell with a 2N (diploid) number of 2.

D. Describe in your own words what happens during transcription. Use the level of detail in section 3.1 “Genetic information flows from DNA to RNA to protein” of How Life Works.

E. Describe in your own words what happens during translation.
Use the level of detail in section 3.1 “Genetic information flows from DNA to RNA to protein” of How Life Works. Make sure you use the following terms in context: codon, amino acid, nucleotide, mRNA.

Explanation / Answer

C. Meiosis is a type of cell divsion n which in the number of chromosomes is halved. It is required for gamete formation during sexual reproduction so that the orginal number of chromosomes of a partcular species is maintained.

Chromosome seggregation is the process in euaryotes by which two sister chromatids formed due to DNA replication or paired homologous chromosomes, separate from each other and migrate to opposte poles of the nucleus.

During Anaphase I of the first meiotic division, the centromeres break down and homologous chromosomes separate. Hence, when cytoknesis occurs, it results in the formation of two daughter cells each with half the number of chromosomes.

But before the separation of the homologous pair of chromosomes an mportant event takes place whch s called 'crossing over'. It occurs during the Pachytene stage of Prophase I of Meiosis I.  

During this stage, the sister chromatids of the homologous pairs 'cross over' and exchange small portons of their strands with each other by forming 'synapses'. This is very important for the genetic varations we see around us. As a result of 'crossng over', when the homologous pairs fnally separate, they are not identical to the parent and the two haploid daughter cells formed have chromosomes whch are not identcal to the parent.

D. Transcrption--

The process of copying genetic information from one strand of DNA into RNA is called transcription.  

*The transcription unit of DNA contains three regions n the DNA--

a. The promoter: It s the binding site for RNA polymerase for initiation of transcription.

b. The structural gene: It codes for enzymes or proteins for structural functons.

c. The terminator: It s the region where transcription ends.

* The DNA dependent RNA polymerase helps in DNA replication by catalysing the polymerisation in only one direction, i.e. 5'----->3'

* The DNA strand that has the polarity 3'--->5' acts as a template and s also called the template strand.

* The strand which does not get transcripted s called the coding strand and has the polarity 5'--->3'. Its sequence is same as RNA. The principle of complementarity governs the process, except that adenosine now base pairs with uracil instead of thyamine.  

* The promoter is located towards the 5'- end [upstream] of the structural gene of the coding strands and provides the binding site for RNA polymerase.

* The sequence of DNA located the 3'- end [downstream] of the coding strand where the process of transcription would stop is called terminator.  

* The structural genes are monocistronic in euaryotes.

* The coding gene sequences called the exons form the part of mRNA and non-coding sequences called introns are removed during RNA splicing.

* In eukaryotes, three types of RNA polymerases are found n the nucleus--

a. RNA polymerase I transcribes for rRNA [ 28S, 18S, and 5.8S]

b. RNA polymerase II transcribes for the precursor of mRNA which s called heterogenous nuclear RNA or hnRNA.

c. RNA polymerase III transcribes tRNA, 5SrRNA, and snRNAs[ small nuclear RNAs].

Translation--  

Translation s the process of synthesis of protein from mRNA with the help of ribosomes. It has three stages--  

a. Intiaton ---

* the ribosomes assemble on the mRNA.

* the amino acids are activated and are delivered to tRNA . One type of tRNA [transferRNA] can carry only one type of amino acid for which it is specified.

b. Elongation-

* Repeated cycles of amino acid delivery by the tRNA takes place according to the code sequence.

* According to the sequence of the codon, amino acids are attached to each other by peptide bonds and a polypeptide chain is formed. This is translocation.

c. Termnation--

* When the A-site of ribosomes reach a termination codon which does not code for any amino acid, no charged tRNA binds to the A-site.

* Dissociation of polypeptide from ribosomes takes place which s catalysed by a 'release factor'. There are three termination codons namely-- UGA, UAG and UAA.  

Related Questions

Navigate

• Browse (All)
• Browse C
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.