Biology 5 Marks Questions

b. Cell name - Functional Megaspore
Nucleus of functional megaspore divides mitotically three times to form 8 free nucleate stage of embryo sac, after this cell walls are laid down leading to 7 celled embryo sac.
c. Development of endosperm in coconut - The two polar nucleii fuses with one male gamete, to produce triploid primary endosperm nucleus (PEN), which divides repeatedly forming free nuclei, subsequently cell wall formation occurs.

During the process of translation in prokaryotes, amino acids are activated in the presence of ATP and they are linked to their aminoacylation of tRNA, as ribosome is the cellular factory for protein synthesis which exists as two subunits for the initiation and this small subunit of ribosome binds to mRNA at the start codon that is AUG. Then it is recognised by initiator 1-RNA, large subunit has two sites for subsequent amino acids to bind to each other with a peptide bond. Then it proceeds towards the elongation process where charged tRNAs sequentially bind to the appropriate codon in mRNA, by forming complementary base pairs with the tRNA anticodon. Then ribosome moves codon by codon along with the m-RNA, and amino acids are added one by one, at the end, a release factor binds to the stop codon which can be UAA/UAG/UGA for terminating the translation.

i. Cutting of the desired gene at a specific location is done by incubating the DNA with specific restriction endonuclease. Restriction enzymes recognise a particular palindromic nucleotide sequence and cut the DNA at that site.
ii. Synthesis of multiple copies of the desired gene is carried out by Polymerase Chain Reaction (PCR)
Amplification of recombinant DNA gene is done using Polymerase Chain Reaction (PCR). It is carried out in the following steps:
a. Denaturation -The double-stranded DNA is denatured by applying high temperature of 95°C for 15 seconds. Each separated strand acts as a template.
b. Annealing - Two sets of primers are added, which anneal to the 3'end of each separated strand.
c. Extension - DNA polymerase extends the primers by adding nucleotides complementary to the template provided in the reaction. Taq polymerase is used in the reaction, which can tolerate heat. All these steps are repeated many times to get several copies of the desired DNA.

Similarities -
Both the processes involve -
i. Unwinding of the helix and separating the two DNA strands
ii. Breaking the hydrogen bonds between the bases / pairs
iii. Follow complimentary base pair rule
iv. Polymerization occurs in 5 → 3' direction
Disimilarities -
DNA replication
i. DNA nucleotides added are ATP, GTP, СТР, ТТР
ii. Deoxyribose sugar is the part of nucleotide
iii. Adenine pairs with Thymine
iv. Both strands copied
v. Resulting into two DNA molecules
Transcription
i. RNA nucleotides added are ATP, GTP, CTP, UTP
ii. Ribose sugar is the part of nucleotide
iii. Adenine with Uracil
iv. Only one strand copied
v. Resulting in formation of an RNA molecule.

a. Double fertilization in angiosperms involves the fusion of two sperm cells with two distinct female gameles:
One of the male gametes, fuses with the nucleus of the egg cell, to form a diploid zygote (syngamy)
Second male gamete, fuses with two polar nuclei, to form (triploid) primary endosperm nucleus (triple fusion)
b. The primary endosperm nucleus undergoes successive nuclear divisions, to give rise to free nuclei / free nuclear endosperm, subsequent cell wall fomation results in cellular endosperm.