3A- Structure of the Nucleic Acids

Question 1

What is a ribose?

Answer 1

it is an organic compound with the formula C5H10O5. It has the aldopentose structural arrangement:

ii. In DNA and RNA, the ribose forms the sugar backbone for the base and the phosphate group. If the 2’ hydroxyl group is absent with the phosphate and base attached, then the structure is a deoxyribonucleic acid (DNA).

Question 2

What is a deoxyribose?

Answer 2

ii. The base on the ribonucleic acid is attached to the 1’ carbon and the phosphate group to the 5’ carbon. If the 2’ carbon lacks a –OH group then the structure is DNA.

Question 3

What is a poly(A) tail?

Answer 3

i. This is a eukaryotic posttranscriptional modification of mRNA that adds multiple adenosine monophosphates to the end of the mRNA strand. It begins at the 3’ strand of the newly made mRNA. Furthermore, there is polyadenylation at multiple sites along the mRNA, which can act like a type of alternative splicing.
ii. The poly(A) tail is important for nuclear export, translation, and stability of the mRNA.

Question 4

What is chromatin?

Answer 4

i. Chromatin is the combination of DNA and proteins that make up the contents of the nucleus of the cell. The function of it is to package DNA into a smaller volume to fit in the cell, to strengthen the DNA to allow mitosis, prevent DNA damage, and to control gene expression and DNA replication.
ii. When DNA contains coding genes that are actively used, then that part of the DNA is more loosely packed, it’s called euchomatin
iii. When the DNA codes inactive genes, it is more tightly packed and termed heterochromatin.

Question 5

What does complementary mean?

Answer 5

i. When two nucleic acid sequences are aligned antiparallel to each other and they match, the nucleotide bases at each position are complementary. This is important during mRNA synthesis and DNA replication, as 1 strand acts as a template for the replication/synthesis and the other strand is said to be complementary to the template strand.

Question 6

What is an anticodon?

Answer 6

i. The anticodon is made up of 3 nucleotides on a tRNA that correspond to 3 bases on the codon of the mRNA. Each tRNA with an anticodon and an amino acid travels to the mRNA template during translation and begins the process of alignment and protein synthesis.

Question 7

What is hybridization?

Answer 7

i. It is the establishment of non-covalent, sequence-specific interactions between 2 or more complementary strands of nucleic acids into a single complex, which in the case of 2 strands is a duplex.
ii. Guanine and cytosine form 3 hydrogen bonds
iii. Adenine and Thyamine form 2 hydrogen bonds
iv. This is commonly used in annealing

Question 8

What is a ribosome?

Answer 8

i. A ribosome is a large complex of RNA and protein that catalyzes protein translation. They are found in all living cells, and in eukaryotes they are free floating in the cytoplasm or bound to the endoplasmic reticulum.
ii. They consist of 2 subunits that work together to translate the mRNA chain during protein synthesis. In prokaryotes, there are the 50s and 30s subunits that make up the 70s ribosome. Their small subunit has an 16s RNA subunit. In eukaryotes there is an 80s ribosome, consisting of a 40s and 60s subunits. The 40s has a 18s RNA and the large has a 5s RNA.

Question 9

What is a histone?

Answer 9

i. Histones are highly alkaline proteins found in eukaryotic cells nuclei. They package and order the DNA into structural units called nucleosomes.
ii. They are the chief component of chromatin, actins as spools around which DNA winds, and play a role in gene regulation.
iii. There are many classes, but the important ones are:
1. H2-H4: the core histones, where DNA wraps around
2. H1 and H5: linker histones, binds nucleons and locks DNA in place.

Question 10

What is a codon?

Answer 10

i. The genetic code gives rise to nucleotide triplets which will specify which amino acid will be added during protein synthesis. Typically, there is 1 codon per amino acid.
ii. To begin translation, there are start codons. The codon AUG is the start codon for eukaryotes.
iii. To stop the translation, there are 3 stop codons. These are UAG, UAA, and UGA

Question 11

What is a nucleosome?

Answer 11

i. A nucleosome is the basic unit of DNA packaging in eukaryotes, consisting of a segment of DNA would around 4 histone cores.

Question 12

What does antiparallel mean?

Answer 12

i. Two complementary strands are deemed antiparallel if they run in opposite directions to one another. One strand is going from 3’-5’ and the other going 5’-3’

Question 13

What is a nucleotide?

Answer 13

i. Nucleotides are molecules that make up the individual structural units of RNA and DNA. They are composed of the base, pentose sugar and the phosphate group.

Question 14

What is a nucleoside?

Answer 14

i. They are structures consisting of a base and a pentose sugar molecule. If there is an adenine base bound to the pentose sugar, it is called adenosine. Guanine with the sugar is called guanosine. And so on…

Question 15

The higher amount of which type of bonding makes DNA stronger?

Answer 15

a. AT have 2 bonds, CG have 3 bonds
b. CG are stronger, therefore DNA that contains higher CG bonds needs a higher temperature to denaturate.

Question 16

What is the general composition of prokaryotic ribosomes?

Answer 16

i. Have a 70s ribosome with 2 separate subunits –> 50s and 30s
ii. the 50s splits into a 5s and 23s, the 30 has the 16s rRNA

Question 17

What is the general composition of eukaryotic ribosomes?

Answer 17

i. Have a 80s ribosome with 2 separate subunits –> 60s and 40s
ii. the 60s contains the 5s and 28s rRNA, the 40s has the 18s rRNA

Question 18

a. The 5’ strand of the DNA contains what group?

Question 19

c. What would occur if there is an addition of a substance to the 3’ carbon of the pentose?

Question 20

e. The 3’ end of the DNA strand has what free floating?

Answer 20

f. -A free -OH of the 3’ pentose

Question 21

Which direction is mRNA transcribed?

Question 22

What is added to the 5’ end of the mRNA?

Answer 22

ii. A guanosine cap is added at the 5’ end for protection

Question 23

Give a general process of mRNA development

Answer 23

iii. Start with a leader sequence –> have start codon –> trancribe coding region –> stop codon –> trailer region –> addition of the polyA tail

Question 24

What are the differences between eukaryotic and prokaryotic mRNA?

Answer 24

iv. prokaryotes don’t have the post-transcriptional modification of the guanosine cap or the polyA tail because transcription and translation occurs together in prokaryotes.

Question 25

What are some general characteristics about tRNA?

Answer 25

i. tRNA carries amino acids to ribosomes and ensure they are incorporated into the appropriate positions in the growing polypeptide chain. The anticodon pairs with the codon of the mRNA and contains the amino acid to grow.
ii. The 5’ base in the anticodon is the “wobble position” which means it may contain an Inosine (I) base which pairs with multiple bases on the codon. However, the other 2 bases on the anticodon ensure that the wobble position only codes for 1 specific amino acid, as there are typically multiple codons for each amino acid.