More Biological Molecules

Question 1

Nucleotide structure of DNA

Answer 1

a pentose sugar
a nitrogen containing organic base
a phosphate group

Question 2

Polynucleotide structure of DNA

Answer 2

-Many nucleotides join together to form polynucleotide strands.
-The nucleotides join up via condensation reaction between the phosphate group of one nucleotide and the sugar of another.
-This forms a phosphodiester bond.
-The chain of phosphates and sugars is known as the sugar-phosphate backbone.

Question 3

DNA structure

Answer 3

Double helix composed of two polypeptides(antiparallel) joined together by H bonds between complimentary bases.

Question 4

Why does DNA replicate?

Answer 4

DNA copies itself before cell division so that each new cell has the fulll amount of DNA. . This means there is genetic continuity between generations of cells

Question 5

Semi Conservative replication

Answer 5

1- DNA helicase causes the two strands od DNA to separate breaking the H bonds between complementary pairs
2- One of the strands is used as the template and complementary base pairing occurs between the template strands and the free nucleotides.
3- Once activated nucleotides are bound, DNA polymerase joins them together forming phosphodiester bonds. The result is that two identical strands of DNA are formed. Each new DNA molecule contains one strand from the original DNA molecule and one new strand.

Question 6

The action of DNA polymerase

Answer 6

Each end of a DNA strand is slightly different in its structure. One end is called the 3’ end of the newly forming DNA strand- so the enzyme can only add nucleotides to the new strand at the 3’ end. This means that the new strand is made in a 5’ to 3’direction and that DNA polymerase moves down the template strand in a 3’ to 5’ direction. (opposite way because strands are antiparallel)

Question 7

What did Meselson and Stahl show?

Answer 7

DNa is replicated using the semi conservative replication method. Their experiment used two isotopes of Nitrogen (DNA contains N) - heavy nitrogen(15N) and light nitrogen (14N)

Question 8

relating dna structure to function

Answer 8

-Very large molecule(can store vast amounts of information)
-Strong sugar phosphate backbone and double stranded(makes the molecule stable so that information it contains is not easily damaged)
-Complimentary base pairing(DNA molecules can reproduce themselves exactly)
-4 base code sequence(Small variations in code sequence can act as a simple code, coding for all amino acids)
-Bases held together by weak H bonds(This means that the chains can separate for replication)
-Coiling of the molecule(Gives DNA a compact shape so that a lot of information cam fit into a small space)