Nucleotides and nucleic acids

Question 1

What bonds join nucleotides?

Answer 1

Phosphodiester bonds

Question 2

What are the 5 key features of our genetic codes?

Answer 2

1. Triplet code - Three bases (a codon) code for one amino acid. The three complementary bases on the tRNA form an anticodon. There are also triplet codes for “start” and “stop” signals.
2. Non-overlapping - Each codon is separate
3. Degenerate - Most amino acids have more than one code
4. Universal - All life on earth has the same DNA code for amino acids
5. Determines amino acid sequence - DNA codes for RNA, which in turn codes for proteins. The proteins produced then form and regulate all other processes.

Question 3

What are the steps of DNA replication?

Answer 3

1. The enzyme DNA HELICASE unwinds the double helix and breaks the hydrogen bonds between strands.
2. Free nucleotides from anything that we’ve eaten are attracted to the exposed complementary bases (by base complementarity) and join with hydrogen bonds.
3. The enzyme DNA polymerase initiates a condensation reaction to create phosphodiester bonds and join the nucleotides together on both new strands.
4. Half of the original DNA is now part of each strand, so this process is semi-conservative.

Question 4

What way (5’ and 3’) can DNA polymerase work, and how does it work in the other direction.

Answer 4

DNA polymerase can only synthesise from 5’ –> 3’, and so it builds DNA continuously on one strand, it has to build discontinuously on the other strand. It has to start from RNA primers as DNA polymerase can only go from existing strands.

Question 5

What are the differences between DNA and RNA in regards to:
Sugar type 
4th base
Shape
Function

Answer 5

DNA: RNA:
Deoxyribose Ribose
Thymine Uracil
Long, compact double-stranded helix | Short, single helix
Contains genetic information Transfers information
in protein synthesis

Question 6

How does the process of protein synthesis take place (Central Dogma) ?

Answer 6

A gene is transcribed in the nucleus by RNA polymerase into mRNA.
This mRNA is then translated on the ribosomes by tRNA into a protein.

Question 7

What is the process of transcription?

Answer 7

Transcription occurs in the nucleus
The DNA unzips in the region of the gene to be transcribed. This is done by DNA helicase.

The ANTISENSE STRAND is template strand for DNA transcription as it gives you a copy of the wanted gene.

Free RNA nucleotides are then attracted by base complementarity
By RNA polymerase ( forms phosphodiester bonds)

Leading to the formation of an mRNA transcript with a sequence identical to the original gene, however with U’s instead of T’s.

mRNA is then released, DNA returns to normal / reforms, and mRNA goes to the ribosomes.

Question 8

What is the process of translation?

Answer 8

1. The ribosome binds to mRNA at a specific area.
2. The ribosome starts matching tRNA anticodon sequences to the mRNA codon sequence.
3. Each time a new tRNA comes into the ribosome, the amino acid that it was carrying gets added to the elongating polypeptide chain.
4. The ribosome continues until it hits a stop sequence, then it releases the polypeptide and the mRNA.
5. The polypeptide forms into its native shape and starts acting as a functional protein in the cell.

Question 9

What is the structure of a nucleotide?

Answer 9

Appropriate sugar (Ribose / Deoxyribose)
A phosphate group
A nitrogenous base

Question 10

What are the key features of tRNA?

Answer 10

Clover leaf shape
3 loops
Anticodon