Bio Quiz 2

• Nitrogen Bases in RNA: Adenine, Guanine, Cytosine, Uracil
• RNA: Ribonucleic acid, single stranded nucleic acid found inside and outside the nucleus of cells

  Structure similar to DNA except:

  RNA has 4 nitrogen bases: Adenine, Guanine, Cytosine, Uracil
• There are three types of RNA:

  1. mRNA: Messanger RNA (found in the nucleus) This molecule carries the genetic message from the nucleus of a cell to the ribosomes.

  
  

  2. tRNA: Transfer RNA (found in the cytoplasm)

  The molecule that brings amino acids to the ribosome to make proteins.

  
  

  3. rRNA: Ribosomal RNA (found at the ribosomes)

  Molecule that helps to make up ribosomes.
• Chromosomes are composed of:

  60% Protein

  35% DNA

  5% RNA
• Gene: Small segment of DNA found on a chromosome that codes for specific traits in organisms.
• Genome: The sum of the entire DNA carried within the cells of an organism.
• Chromosomes consist of the following:

  -One linear double stranded DNA molecule

  -Proteins called histones
• The DNA is wrapped around a group of 8 histone molecules making a "bead-like" structure called Nucleosome.

  The nucleosomes fold back upon themselves making a condensed structure called chromosome.
• Each gene is composed of two portions:

  1. Exons: These are portions of DNA in a gene that are called "Coding Regions". These portions code for specific proteins within a cell.
  2. Introns: There are portions of DNA in a gene that are "noncoding". They are like spaces between the coding regions. Most of the structure of a gene is made up of these introns that were once called "junk" or "nonsense" DNA.
• DNA replication is semi-conservative. This means that when DNA is copied, each new molecule created contains one strand of parental DNA and one strand of new DNA.
• DNA is copied through the following 4 steps:

  1. Initiation
  2. Elongation
  3. Termination
  4. Proofreading and Correction
• Initiation is the opening up of the DNA molecule so new nucleotides can be inserted to eventually create 2 new strands.

  At a specific sequence of nucleotides called the replication origin, enzymes called helicases unzip and open up the DNA creating replication forks.

  DNA polymerase inserts itself in the replication fork and begins to add new nucleotides, one at a time, to create a new complementary strand.