BIOLOGY CHAPTER 12 DNA PRESENTATION

RNA

• It contains the sugar ribose, the base uracil replaces thymine, and usually is a single strand
• Three major types of RNA that are found in living cells:
• Messenger RNA (mRNA) molecules are long strands of RNA nucleotides that are formed complementary to one strand of DNA.
• Ribosomal RNA (rRNA) is the type of RNA that associates with proteins to form ribosomes in the cytoplasm.
• Transfer RNA (tRNA) are smaller segments of RNA nucleotides that transport amino acids to the ribosome.

NUCLEOTIDES

• Nucleotides are the subunits of nucleic acids and consist of a five-carbon sugar, a phosphate group, and a nitrogenous base.
• DNA nucleotides contain the sugar deoxyribose, a phosphate, and one of four nitrogenous bases: adenine, guanine, cytosine, or thymine.
• RNA nucleotides contain the sugar ribose, a phosphate, and one of four nitrogenous bases: adenine, guanine, cytosine, or uracil.
• Guanine (G) and adenine (A) are double-ringed bases. This type of base is called a purine base.
• Thymine (T), cytosine (C), and uracil (U) are single-ringed bases called pyrimidine bases.

DOUBLE HELIX

• A twisted ladder shape, formed by two strands of nucleotides twisted around each other.
• The specific structure of the DNA double helix was determined later by Watson and Crick when they used franklin's data and other mathematical data.
• DNA is the genetic material of all organisms, composed of two complementary, precisely paired strands of nucleotides wound in a double helix.

DNA STRUCTURE

• DNA often is compared to a twisted ladder, with the rails of the ladder represented by the alternating deoxyribose and phosphate.
• The pairs of bases (cytosine---guanine or thymine---adenine) form the steps, or rungs, of the ladder.
• Cytosine and thymine are pyrimidine bases, adenine and guanine are purines, and C=G and A=T.

UNWINDING

• DNA helicase, an enzyme, is responsible for unwinding and unzipping the double helix.
• When the double helix is unzipped, the hydrogen bonds between the bases are broken, leaving single strands of DNA.
• Proteins called single-stranded binding proteins associate with the DNA to keep the strands separate during replication.
• As the helix unwinds, another enzyme, RNA primase, adds a short segment of RNA, called an RNA primer, on each DNA strand.

SEMICONSERVATIVE REPLICATION

• During semiconservative replication, parental strands of DNA separate, serve as templates, and produce.
• The process of semiconservative replication occurs in three main stages: unwinding, base pairing, and joining.