Chapter 3- Nucleotides and nucleic acids

Question 1

What is the structure of a nucleotide?

Answer 1

1 pentose sugar- 5 carbon sugar, DNA= deoxyribose and in RNA= ribose
Nitrogenous bases- Adenine, Thymine, Cytosine, Guanine and in RNA Uracil
Phosphate group

Question 2

What is the bond between two nucleotides?

Answer 2

Phosphodiester bond between carbon 3 (H) of the nucloteide sugar and carbon 5 (OH) on the secon

Question 3

What are purines?

Answer 3

Larger
Composed of 2 carbon rings
Only bond with specific pyrimadines
Adenine and Guanine

Question 4

What are pyrimidines?

Answer 4

Smaller
Composed of 1 carbon ring
Thymine, Cytosine and Uracil

Question 5

How many hydrogen bonds do the specific complementary base pairs have/

Answer 5

Adenine and Thymine= 2 hydrogen bonds

Guanine and Cytosine= 3 hydrogen bonds

Question 6

What is the role of DNA replication?

Answer 6

Ensures that new cells are made in mitosis contain genetically identical information

Question 7

How does DNA replication occur?

Answer 7

1- At the start of the process, the DNA in the parent cell is in tact and bound by hydrogen and phosphodiester bonds
2- An enzyme called DNA helicase breaks the hydrogen bonds between the bases and each strand of DNA is now exposed
3- Free nitrogenous bases in the nucleus will bind to each side of the exposed DNA strands and so the hydrogen bonds reform
4- DNA polymerase will allow each nucleotide to bind forming phosphodiester bonds
This process is semi-conservative

Question 8

What are the key characteristics of the genetic code?

Answer 8

Universal- all organisms use it to form proteins
Degenerate- only 20 different AAs and 64 possible communications
Non-overlapping- bases are always read in codons

Question 9

What are the steps of transcription?

Answer 9

1- DNA will unzip and expose the anti-sense strand
2- Free RNA nucleotides will bind to the exposed bases
3- A different helicase enzyme is used to break hydrogen bonds when compared to DNA replication
4- RNA polymerase reforms the phosphodiester bonds in order to connect the mRNA strand together
5- Once the code has been copied, the mRNA molecule detaches and leaves via nuclear pores

Question 10

What are the steps of translation?

Answer 10

1- mRNA binds to the ribosome
2- The ribosome moves along the mRNA and reads each codon one at a time
3- tRNA will bring the correct anti-codon to bind to the start mRNA
4- When the anti-codon binds, it brings AA1 closer to AA2
5- A peptide bond will form if peptidyl transferase is present
6- Process continues until a stop codon is reached
7- Once the protein is formed, it can be modified or ejected from the cell