DNA vs RNA

DNA	RNA
Located only in the nucleus Double stranded Transmits genetic material from 1 generation to another Directs all cellular metabolism	can be in the whole cell single stranded responsible for protein synthesis enzymes – catalyse that initiate the action of the cell

DNA

DNA : deoxyribonucleic acid -  The  double stranded molecule that encodes genetic information.  It transmits genetic information from 1 generation to another

• nucleotides - Contains phosphate and sugar that form the backbone of the ladder and the nitrogenous bases that form the steps
•  DNA is a double-stranded molecule held together by bonds between base pairs of nucleotides
• The four nucleotides in DNA contain the nitrogenous bases:
  • purines
1. adenine (A)
2. guanine (G) 
• pyrimidines

3.     cytosine (C)

4.     thymine (T)

• In nature, base pairs form only between:
  • A and T (held together with double Hydrogen bond)
  • G and C (held together with triple Hydrogen bond)

Gene - a segment of DNA found on a chromosome that codes for a particular protein

• Several pairs of bases
• a unit of heredity

DNA replication :

the process of duplicating the genetic material prior to its distributtion in Mitosis or Meisosis

Steps in DNA replication:

1. process begins as an enzyme breaks the attachments between the 2 strands of DNA
2. moving along the DNA, the enzyme unzips the halves of DNA
3. procedding in opposite directions on each side, the enzyme DNA polymerase moves down the length of DNA , attching new DNA nucleotides into position
4. the DNA polymerase also makes sure that no mistakes are made in the attachhment of the new DNA nucleotides
5. replication proceeds in both directions appearing as bubbles
6. the complementary molecule pair with the exposed nitrogenous bases of both DNA strands
7. once properly aligned, a bond is formed between the sugars and phosphates of the newely positioned nucleotides.  A strong sugar and phosphate backbone is formed in the process
8. this process continues until all replication bubbles join

Normal DNA will have a short bond joined with a long bond which creates a perfect ladder :

Long Bonds :  G and A

Short Bonds : T and C

DNA polymerase - any of several polymerases that promote replication or repair of DNA usually using single-stranded DNA as a template

 

Cell Cycle:

INTERPHASE : The period in the cell cycle when the cell is not reproducing (undergoing mitosis). The Resting Phase. During this time, the cell is growing rapidly, increasing its size, making new molecules, and doing all of the things that cells do that are not associated with cell division. The period is subdivided into the G1 phase, the S phase, and the G2 phase.

G1 Phase (Gap 1) – where the cell spends most of its normal life (different amounts of time for different types of cells)

• most variable part of the cell cycle
• 2n is the DNA number in this cycle
• RNA is synthesized
• Enzymes and proteins are produced for synthesis of DNA
• Cells that have lost their ability to reproduce (permanently) such as nerve and muscle cells leave the cell cycle at this point and enter G0
• Cells that are temporarily noncycling leave the cell cycle at G1 and enter GQ (quiescent cells such as liver and bone)

S Phase (Synthesis) – synthesis of DNA takes place

• Proteins produced to maintain DNA synthesis
• RNA synthesis continues
• Maturation and reproduction of centrioles
• About 15 hours
• 4n is DNA number
• most radioresistant phase

G2 Phase (Gap 2) – cell takes an inventory of itself

• checkpoint gene -  examines DNA content and reverses damage or corrects DNA
• proteins needed for mitosis are synthesized
• synthesis of RNA that will direct synthesis of proteins for mitosis
• centrioles divide into pairs
• 2^nd most radiosensitive stage

MITOSIS (M phase) - cell division in which the nucleus divides into nuclei containing the same number of chromosomes

• RNA synthesis stops
• Condensation and segregation of DNA, RNA and proteins
• Protein synthesis decreases
• 5 – 10% of cell cycle
• Most radiosensitive stage
  • Past G2 checkpoint
  • Most stressful part of a cells life