DNA Structure and Function

• DNA stands for deoxyribose nucleic acid

• DNA controls all the chemical changes which take place in cells

• The kind of cell which is formed, (muscle, blood, nerve etc) is controlled by DNA

• The kind of organism which is produced (buttercup, giraffe, herring, human etc) is controlled by DNA

• No two people (except identical twins) have the exact same DNA

• DNA is a nucleic acid, found in chromosomes, in the nucleus of your cells.

• Most human cells have 23 pairs of chromosomes, or 46 total

• Exception is sperm and egg cells which have only 23 chromosomes because they are not in pairs

• Each chromosome pair can be broken into smaller segments called genes.

• Genes control the traits of the organism, and therefore can vary between individuals.

DNA Structure

• It is a POLYMER -long repeating chain of monomers (remember that POLY means MANY and MONO means ONE)

• POLYNUCLEOTIDE or a NUCLEIC ACID

• There are two main types of nucleic acids: DNA and RNA

• The Monomer (the unit repeating on a polymer) of a nucleic acid is called a nucleotide.

• A nucleotide: three parts which are sugar, phosphate, and base

Genetic Code

• DNA has four different nitrogenous bases

  • Adenine

  • Thymine

  • Guanine

  • Cytosine

• These bases form pairs according to the base pairing rule

  • Adenine binds only with Thymine

  • Cytosine binds only with Guanine

  • These pairs are considered to be complementary

  • DNA is made when these two strands twist together in a shape called the double helix

  • The sides of the helix (backbone) are made up of alternating sugar and phosphate molecules

  • The sugar in DNA is called deoxyribose from which DNA got its name

  • The rungs of the helix are made up of the paired nitrogenous bases (a-t and c-g) which help to code the DNA with instructions for the cell

  • Adenine and Thymine have 2 hydrogen bonds

  • Cytosine and Guanine have 3 hydrogen bonds

• Complementary strands

  • Because sugar phosphate sequence does not change, we abbreviate the DNA code by the writing the sequence of bases

• How it works

  • DNA is replicated, it is transcribed into RNA and then is translated into a protein

  • DNA replication

    • Before a cell divides, the DNA strands unwind and separate

    • Each strand makes a new partner by adding the appropriate nucleotides

    • The result is that there are now two double-stranded DNA molecules in the nucleus so that when the cell divides, each nucleus contains identical DNA

    • Each strand builds up its partner by adding the appropriate nucleotides

  • Transcription and Translation

    • HOW DOES DNA CODE FOR AND PRODUCE PROTEIN?

    • TRANSCRIPTION and TRANSLATION take the information in DNA and use it to produce proteins.

    • 1. TRANSCRIPTION uses a strand of DNA as a template to build a molecule called messenger RNA (mRNA)

    • 2. TRANSLATION - translates the code that the messenger RNA (mRNA) carries into a sequence of AMINO ACIDS to build a PROTEIN.

  • What is RNA

    • RNA stands for RiboNucleic Acid

    • Like DNA, RNA is a POLYMER known as a NUCLEIC ACID made of repeating NUCLEOTIDES. (Remember, a NUCLEOTIDE has three parts: a PHOSPHATE, SUGAR, and a NITROGENOUS BASE.)

    • HOW DOES RNA DIFFER FROM DNA? Instead of the DNA sugar deoxyribose, the sugar in RNA IS RIBOSE Instead of being double stranded like DNA, RNA is SINGLE STRANDED. Instead of the DNA bases being ATCG, the RNA bases are AUCG. THYMINE (T) is replaced by URACIL (U)

  • Transcription

    • The process where messenger RNA (mRNA) is made by copying the DNA code for one gene. This process occurs in the nucleus

    • Each gene in your DNA nodes for the production of a different protein

    • Genes code for proteins

    • Proteins are polymers of amino acids

    • Amino acids are the building blocks of proteins or the monomers

    • There are 20 amino acids

  • Translation

    • Translates the code that the mRNA carries into a sequence of amino acids to builds a protein

    • The mRNA carries the code out of the nucleus to a ribosome in the cytoplasm. The tRNA that complements the mRNA will attach the appropriate amino acid in the sequence

    • Codon: three mRNA bases code for an amino acid

    • Start codon: AUG

    • Stop codon: UAA, UGA, UAG