1. Comparison Of DNA And RNA Synthesis in Prokaryotes and Eukaryotes
Dr Shumaila Asim
Lecture # 09

2. Comparison of characteristic features of DNA synthesis in Prokaryotes and Eukaryotes
Comparison of characteristic features of DNA synthesis features of RNA synthesis
Biochemical features and characteristic roles of different types of RNA
mRNA
tRNA
rRNA

3. Replication
DNA
Transcription
RNA
Translation
PROTEIN

4. DNA Replication
Process of duplication of the entire genome prior to cell division
Biological significance
extreme accuracy of DNA replication is necessary in order to preserve the integrity of the genome in successive generations
In eukaryotes , replication only occurs during the S phase of the cell cycle.
Replication rate in eukaryotes is slower resulting in a higher fidelity/accuracy of replication in eukaryotes

5. Comparison of Replication
Features
Prokaryotes
Eukaryotes
RNA primer length
50 nucleotides
9 nucleotides
DNA polymerase
I,II,III
α,β,γ,δ,ε
Number of origins
Single
Multiple
Nucleotide length of Okazaki
nucleotides
200 nucleotides
Rate of replication
500 nucleotides/sec
50 nucleotides/sec

6. Continued….. Prokaryotes Eukaryotes 1. It occurs inside the cytoplasm.
1. It occurs inside the nucleus.
2. There is single origin of replication.
2. Origin of replications are numerous.
3. DNA polymerase III carries out both
initiation and elongation.
3. Initiation is carried out by DNA
polymerase α while elongation by
DNA polymerase δ and ε.
4. DNA repair and gap filling are done
by DNA polymerase I.
4. The same are performed by DNA
polymerase β.
5. RNA primer is removed by DNA
polymerase I.
6. Okazaki fragments are large, 1000-
2000 nucleotides long.
6. Okazaki fragments are short, 100-
200 nucleotides long.
7. Replication is very rapid, some 2000
base pairs per second.
7. Replication is slow, some 100
nucleotides per second.
8. DNA gyrase is needed.
8. DNA gyrase is not needed.

7. Differences between prokaryotic and eukaryotic DNA replication

12. Prokaryotes and Eukaryotes

13. Comparison of Replication & Transcription
Cell division is essential for an organism to grow, but when a cell divides it must replicate the DNA in its genome so that the two daughter cells have the same genetic information as their parent. DNA provides a simple mechanism for replication.
In transcription, or RNA synthesis, the codons of a gene are copied into messenger RNA by RNA polymerase.
As opposed to DNA replication, transcription results in an RNA complement that includes uracil (U) in all instances where thymine (T) would have occurred in a DNA complement.

14. Replication
Transcription
Purpose
The purpose of replication is to conserve the entire genome for next generation.
Definition
DNA replication is the replication of a strand of DNA into two daughter strands, each daughter strand contains half of the original DNA double helix.
The purpose of transcription is to make RNA copies of individual genes that the cell can use in the biochemistry.
Uses the genes as templates to produce several functional forms of RNA

15. Replication
Transcription
Products
One strand of DNA becomes 2 daughter strands.
Product processing
In eukaryotes complementary base pair nucleotides bond with the sense or antisense strand. Thesre are then connected with phosphodiester bonds by DNA helix to create a complete strand.
mRNA, tRNA, rRNA and non-coding RNA( like microRNA)
A 5’ cap is added, a 3’ poly A tail is added and introns are spliced out.

16. Transcription
Replication
Base Pairing
Since there are 4 bases in 3-letter combinations, there are 64 possible codons (43 combinations).
Codons
These encode the twenty standard amino acids, giving most amino acids more than one possible codon. There are also three 'stop' or 'nonsense' codons signifying the end of the coding region; these are the UAA, UAG and UGA codons.
RNA transcription follows base pairing rules. The enzyme makes the complementary strand by finding the correct base through complementary base pairing, and bonding it onto the original strand.
DNA polymerases can only extend a DNA

17. Transcription
Replication
Result
In replication, the end result is two daughter cells.
Enzymes
The two strands are separated and then each strand's complementary DNA sequence is recreated by an enzyme called DNA polymerase.
While in transcription, the end result is a RNA molecule.
In transcription, the codons of a gene are copied into messenger RNA by RNA polymerase.This RNA copy is then decoded by a ribosome that reads the RNA sequence by base-pairing the messenger RNA to transfer RNA, which carries amino acids.

18. Replication
Transcription
Enzymes Required
DNA Helicase, DNA Polymerase.
Product
Replication is the duplication of two-strands of DNA.
Transcriptase (type of DNA Helicase), RNA polymerase.
Transcription is the formation of single, identical RNA from the two-stranded DNA

24. mature mRNA in eukaryotes:
5’ cap
After nucleotides have been synthesized, the 5’-end of the mRNA is capped 5’ to 5’ with a guanine nucleotide
Results in the addition of two methyl (CH3) groups.
Essential for the ribosome to bind to the 5’ end of the mRNA.
Poly (A) tail
adenine nucleotides are added to 3’ end of mRNA.
Complex enzymatic reaction.
Stabilizes the mRNA, and plays an important role in transcription termination.
Introns (non-coding sequences between exons) are removed and exons (amino acid coding sequences) are spliced.

29. Cells contain thousands of ribosomes.
Consist of two subunits (large and small) in prokaryotes and eukaryotes, in combination with ribosomal proteins.
E. coli 70S model:
50S subunit = 23S (2,904 nt) + 5S (120 nt) + 34 proteins
30S subunit = 16S (1,542 nt) + 20 proteins
Mammalian 80S model:
60S subunit = 28S (4,700 nt) +5.8S (156 nt) + 5S (120 nt) + 50 proteins
40S subunit = 18S (1,900 nt) + 35 proteins
DNA regions that code for rRNA are called ribosomal DNA (rDNA).