Types Of DNA Replication

Look! We have three types of DNA replication .

1. Conservative
2. Semi Conservative
3. Dispersive

Haa what are they? why DNA replications are grouped into three types? what is the differences?

1. Conservative
- The original (parental) DNA molecule are preserved and entire new copy is made.


2. Semi Conservative
- DNA molecule produced contain one parental strand and one new strand .

3. Dispersive
- Each daughter strand produced contain a mixture of parental and new fragments of DNA . 

KINGDOM PROTISTA

KINGDOM PROTISTA

Unique characteristics of protista :

• unicellular and aquatic eukaryotes
• can live singly or occur in colonial
• contain typical cell organelle such as mitochondria,nucleus and Golgi apparatus
• they are flagellate with 9+2 internalmicrotubular structure

Lactose Operon

   

(a) Process when Lactose absent
(b) Process when Lactose present

Regulator gene ( R ) : contain genetic information for the synthesis of protein called repressor .
Promoter ( P )           : Site for the attachment of RNA polymerase 
Operator ( O )           : site for the attachment of the repressor protein .
Structural Genes (S) : One to several genes determining the amino acids sequence of the protein

• (1) : lacZ - Produces B- galactosidase that functional to converts lactose to glucose & galactose          

• (2) : lacY - Produces Lactose permease that functional as transport lactose into the cell 

• (3) : lacA - Produce transacetylase that  used to transfer an aceytl group CO-A to B -galactosidase      

Operon                       : A group of structural genes and regulating genes that  function as a unit .
                                         ( OPERON = Structural gene + Operator + Promoter )

(a) Process when Lactose absent 

1. The repressor attaches itself to the operator and blocked part of promoter .
2. RNA Polymerase cannot bind to the promoter
3. The operon is not active because transcription is blocked by repressor-operator complex.
4.  No transcription occur and the 3 structural enzymes cannot be synthesized.

(b) Process when Lactose Present 

1. Lactose enter to E.coli and converted to Allolactose ( isomer of lactose )
2. Allolactose binds to the repressor protein which is produced by regulator gene.
3. The repressor protein changes shapes and it cannot bind to the operator that causes the operon is activated.
4. RNA polymerase binds to promoter .
5. Transcription of structural genes takes place to form mRNA
6. The translation of mRNA occur
7. The enzymes B-galactosidase , permease and transacetylase are produced
8. Lactose is hydrolysed into galactose and glucose .

DNA REPLICATION

Process Of  DNA Replication

There are five step process of DNA Replication :

1. SEPARATION OF DNA DOUBLE HELIX 

•  DNA Helicase binds to origins cause the DNA double helix to unwind. The H bond between nitrogenous bases break causing DNA strand to separate . Each strand serves as a template. Replication occurs from 5' to 3' end . 

• Single-Strand Binding Proteins ( SSBP ) are  functional as prevent the DNA strands from rejoining .

• Topoisomerase are functional as relieves strain due to supercoiling of DNA molecule form.

     2.  BUILDING A PRIMER

• RNA  Primase adds a short RNA Primer and used as the primer for DNA Synthesis

      3. ASSEMBLING A COMPLEMENTARY STRANDS

• DNA Polymerase III add DNA Nucleotide to the RNA Primer .
• The free nucleotides pair up with the complementary bases in the parental DNA strand
• Base adenine pairs with thymine and cytosine pairs with guanine. 

• DNA Synthesis in continuous manner towards the replication fork is called leading strand while the other strands , DNA is discontinuously away from replication fork is called lagging strand .

• Produces  short fragments called Okazaki fragment 

     4. REMOVING THE PRIMER

• DNA Polymerase I   remove RNA Primers and replaced by DNA nucleotide .

     5. JOINING THE OKAZAKI FRAGMENTS  

• DNA Ligase catalyzes the formation of a phosphodiester bond between two Okazaki fragments
• Two identical strands of DNA are formed .