Answer:
Watson and Crick proposed the double helical model of DNA.
Explanation:
- This model says that DNA exist as double helix. It has two polynucelotide strands running in opposite direction i.e the strands are anti-parallel.
- Each polynucleotide strand is made up of several nucleotide liknked together by phophodiester bonds.
- The two strands are not coiled upon each other but the double strand is coiled upon itself around a common axis like the spiral stair case. Here base pairs forms the stairs and backbone of two strands form railing. Back bone contains sugar and phosphate.
- The base pairing is specific, adenine always pairs with thymine and guanine always pairs with cytosine. Thus if we see any base pair, it consists of one purine and one pyrimidine.
- The two strands of DNA thus show complementary base pairing.
- The strands are held together because of hydrogen bonding between the bases in opposite strand.
- One full helical turn involves ten base pairs and the base pairs are stacked 3.4 A apart.
- This form is called as B-form of DNA.
Answer:
the centrioles are at opposite poles of the cell
the pairs of homologous chromosomes become arranged on a plane equidistant from the poles called the metaphase plate
spindle fibers from one pole of the cell attach to one chromosome of each pair and spindle fibers from the opposite poles attach to the homologous chromosomes
A Dew forms on grass when water vapor forms when molecules cool and join together.
B Gases expand when heated and contract when cooled.
Answer: Wavelength, wave period, and wave frequency.
