DNA Replication: Initiation,Elongation,Termination

Act I 

Initiation

Helicase splits/opens the template DNA strand at the replication fork = creation of bubble

Single-strand binding proteins stabilize the unwound parental DNA , otherwise there is a risk the strands will bond back together

A lot of tension has built up , from parts of the DNA strands being straightened. The gyrase cuts the stands to release tension

RNA primase creates RNA primers that act as a starting point for replication

The DNA polymerase III recognize the primers

Act II

Elongation 

The parental strands are replicated  in the direction of 5' to 3' 

Leading strand- Polymerase III begins adding nucleotides to the RNA primer in the direction of the opening  replication fork, it does this continuously

The lagging strand waits for enough of the replication fork to open ...... when it has opened sufficiently a DNA primer  attaches to the parental strand and polymerase III  makes a new starting point( discontinuous process)

The second strand is composed of  Okazaki fragments ( 100-200 nucleotides long) and RNA  primers 

Lagging= discontinuous, RNA primers, Okazaki fragments , polymerase III

Leading= continuous, 1 Primer, Polymerase III

The two new strands are assembled in the opposite direction

Act III

Termination 

Polymerase I removes the RNA nucelotides  one at a time, replacing them with DNA nucleotides, this process is catalyzed by DNA ligase 

Polymerase I and polymerase II( slow enzyme)  are repair mechanisms, they work to repair damage done to DNA during replication, and proofread

Catabolism & Anabolism

Catabolism

• Chemical reactions that result in the break down of complex organic molecules into simpler substances
• Releases energy that is used to start chemical reactions

Anabolism

• Simpler substances combine to become more complex
• requires energy
• build new molecules
• store energy

* Energy from catabolic reactions is used for anabolic reactions

Anabolic + catabolic=Metabolism 

Non-Cyclic

Anabolic reaction

Cyclic

Anabolic reactiom

Calvin Cycle

Anabolic reaction

Glycolosis

Catabolic reaction

Catabolic reaction

Krebs

Catabolic reaction

The Sad But True Story:Of The Passenger Pigeon

The Sad But True Story: Of The Passenger Pigeon (Ectopistes migratorius)





The passenger bird once constituted an estimated 25-40 % of America's bird population

When Europeans first discovered America there were 3-5 billion passenger pigeons

Never again will  a passenger pigeon soar through the sky... as 100 years ago they became extinct

Millions of these magnificent birds would travel in one flock.One flock traveling at sixty miles an hour would take several days to pass over a particular area.

 When they  migrated in  March and April one flock could block out the sun, making the sky dark for days.



The passenger pigeons had almost no defense mechanism, so they would travel in mass flocks as a means of protection against predators.

They would roost and feed in hardwood forests, until their natural habitat started being diminished and turned into farmland. Causing the pigeons to land on farmer's fields.

Humans started to kill passenger pigeons
- To protect their crop from being eaten
-  they were a cheap source of food , which was great for feeding slaves




The real slaughter of passenger pigeons started in the 1800's
They were :

• netted by baiting traps
• shot at nesting sites
• knocked out of  trees with long sticks
• the fumes of sulfur would case the birds to become dazed and fall out of trees

By using trains hunters could track and follow the flock giving them no rest and no time to mate and care for their young

In Michigan 50 000 pigeons were killed per day for 5 consecutive months.

In 1860 the decrease in population was noticeable, but nothing was successfully done to  protect their species

By 1890 they were considered a rare species, with only a few thousand remaining

A Glimpse of Hope

Finally the voice of conservationists was heard and a bill was passed  in Michigan,   making it illegal to net pigeons within two miles of a nesting area

However this law was hardly enforced... and the mass hunting continued

 In 1897 a ten year hunting ban on passenger pigeons began 

 It Was Too Late

 Despite conservationists efforts
 Not being able to breed and protect their blind and now defenseless young ,the population plummeted

Without a large flock the pigeons were defenseless to prey and unable to follow normal migration and mating habits

By 1914 only one of the species remained

Never again will man witness the beauty of  millions of passenger pigeons filling the sky above




Last of her species, died at 1 p.m.,
1 September 1914, age 29, in the
Cincinnati Zoological Garden.