MEIOSIS

• The first division (meiosis 1) produces two cells with half the number of chromosomes as the parent cell, while the second division (meiosis 2) produces four haploid daughter cells.
• DNA DISCOVERY AND STRUCTURE

  • James Watson and Francis Crick worked out the structure of DNA in 1953 by using data from other scientists (Rosalind Franklin and Maurice Wilkins) they were able to build a model of DNA. ​
  • The X-ray crystallography data they used showed that DNA consists of two strands coiled into a double helix.
  • DNA is a polymer made from four different nucleotides. These are arranged in a repeating fashion. Each nucleotide consists of alternating sugar and phosphate sections with one of the four different bases attached to the sugar.

  
• • The DNA strand is unwound and separated by an enzyme called helicase.

  The separation is completed by breaking the hydrogen bonds between the base pairs DNA REPLICATION

  
• DNA REPLICATION

  • Begins at Origins of Replication
  • Two strands open forming Replication Forks (Y-shaped region)
  • New strands grow at the forks

  
• Process of DNA replication:

  1. The DNA strand is unwound and separated by an enzyme called helicase.

  2. Separation is completed by breaking the hydrogen bonds between the base pairs.

  3. The leading strand is synthesized continuously.

  4. The lagging strand is synthesized in short fragments that are ultimately stitched together using the enzyme ligase.

  5. Free nucleotides found in the nucleus are added to the strands of DNA by an enzyme called DNA polymerase.

  6. Nucleotides are added to complementary bases on the DNA template strands according to base-pairing rules.

  7. Bases are added in one direction on one strand and in the opposite direction on the other strand.

  8. The newly formed DNA strands rewind to form a double-helix spiral staircase shape once again.
• SUMMARY + ENZYMES 

  • Helicase unzips the DNA double helix
  • Primase lays down the RNA primers 
  • DNA polymerase 
  • Ligase acts as glue and helps turn the discontinuous synthesize of the lagging strand become continuous

  
• Transcription takes place in the nucleus and occurs in a series of stages
• Transcription is the process where the base sequence of DNA is copied or transcribed into mRNA (messenger RNA)
• During transcription:

  • The two strands of the DNA helix are unzipped by breaking weak Hydrogen bonds between base pairs
  • The unwinding of the helix is caused by an enzyme called helicase enzyme
  • RNA polymerase attaches to the DNA in a non-coding region just before the gene
  • RNA polymerase moves along the DNA strand, and free RNA nucleotides form hydrogen bonds with the exposed DNA strand nucleotides by complementary base pairing to form a strand of mRNA
• In transcription, RNA nucleotides contain the same bases as DNA, except that T is replaced by U. U base pairs with A
• The strand of mRNA formed during transcription is an opposite copy of the DNA strand, with U replacing T. This is known as a complementary copy
• The newly formed strand of mRNA is ready to leave the nucleus and travel to the ribosome for translation
• During translation, the mRNA strand travels through the cytoplasm and attaches to the ribosome
• The mRNA strand passes through the ribosome
• For every three mRNA bases, the ribosome lines up one complementary molecule of tRNA, which we call a codon
• tRNA molecules transport specific amino acids to the ribosome and leave them behind after lining up opposite the DNA
• The relationship between three mRNA bases and one tRNA molecule is known as the triplet code
• Used tRNA molecules exit the ribosome and collect another specific amino acid
• A chain of several hundred amino acids, in the correct order according to the original DNA, is made during translation, forming a polypeptide
• After translation, the polypeptide is folded into the correct shape and becomes a protein
• Peptide bonds form between the adjacent amino acids to finalize the protein's structure
• Meiosis involves two rounds of nuclear division, producing four genetically distinct daughter cells with only one copy of each chromosome.