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:
Proteins can carry nutrients across the plasma membrane. There are also differnet receptros outside the cell that recieve signals as well as inside the cell.
Explanation:
Answer:
D
an increase in the length of the fatty acid tails.
Explanation:
As average annual temperatures decrease, we would expect to find phospholipids within the cell membranes of organisms to have both saturated
and unsaturated fatty acid tails. Saturated fatty acids tails are arranged linearly, in a way that maximizes interactions between the tails and
decreases bilayer fluidity. Unsaturated fatty acids, on the other hand, have more distance between the tails, fewer intermolecular interactions and
more membrane fluidity. Longer tails and decreased cholesterol also decrease fluidity
