CHAPTER 12 DNA (Deoxyribonucleic Acid)

BUILDING BLOCKS (MONOMERS) DNA is made up of repeating units called NUCLEOTIDES. Each NUCLEOTIDE contains 3 parts 1. SUGAR GROUP—(deoxyribose) always the same 2. PHOSPHATE GROUP- always the same 3. NITROGEN CONTAINING BASE these vary (Can be ADENINE, GUANINE, CYTOSINE, or THYMINE)

DNA Nucleotide O O=P-O N CH2 O C1 C4 C3 C2 Phosphate Group Nitrogenous base (A, G, C, or T) CH2 O C1 C4 C3 C2 5 Sugar (deoxyribose)

MONOMERS becoming POLYMERS NUCLEOTIDES form long chains by the phosphate group of one nucleotide forming a COVALENT BOND with the SUGAR GROUP of another NUCLEOTIDE (this can occur in any random order of ACTGCTAAATCGC) “Remember that COVALENT BONDS are VERY STRONG “

NITROGENOUS BASES PURINES- nitrogenous bases that have TWO rings of carbon (EXAMPLES- ADENINE and GUANINE) PYRIMIDINES- nitrogenous bases that have only one ring of carbon (EXAMPLES- THYMINE and CYTOSINE)

Nitrogenous Bases A or G T or C PURINES 1. Adenine (A) 2. Guanine (G) PYRIMIDINES 3. Thymine (T) 4. Cytosine (C) A or G T or C

Combining strands of DNA PURINES always form HYDROGEN BONDS with PYRIMIDINES in a specific way **Remember hydrogen bonds can be easily broken We call this the “COMPLEMENTARY BASE PAIR RULES” ADENINE can only bond with THYMINE GUANINE can only bond with CYTOSINE

DNA Double Helix P O 1 2 3 4 5 P O 1 2 3 4 5 G C T A

Two strands together form a DNA DOUBLE HELIX shape Nitrogenous Base (A,T,G or C) “Rungs of ladder” “Legs of ladder” Phosphate & Sugar Backbone

WATSON and CRICK The first scientists to identify the shape of DNA as a DOUBLE HELIX. Won the Nobel Prize in 1962

DNA Replication DNA must be copied The DNA molecule produces 2 IDENTICAL new complementary strands following the rules of base pairing: A-T, G-C Each strand of the original DNA serves as a template for the new strand See p. 298

DNA Replication DNA must be copied The DNA molecule produces 2 IDENTICAL new complementary strands following the rules of base pairing: A-T, G-C Each strand of the original DNA serves as a template for the new strand See p. 298

STEPS IN REPLICATION (pg 188) TWO DNA STRANDS SEPARATE due to an ENZYME called HELICASES TWO strands of DNA are used as TEMPLATES for new strands ENZYMES called DNA POLYMERASE help to “GLUE” the proper nucleotides in place TWO IDENTICAL DNA STRANDS are formed

DNA Replication DNA Template New DNA Parental DNA

ASSIGNMENT Draw a strand of DNA—in pen Draw a second strand of DNA with the proper COMPLIMENTARY BASE PAIRS SHOW your DNA go thru one round of REPLICATION

RNA vs. DNA DNA Double stranded Deoxyribose sugar Bases: C,G A,T RNA Single stranded RIBOSE SUGAR Bases: C,G,A,URACIL Both contain a sugar, phosphate, and base.

Types of RNA (3) MESSENGER RNA- carries info from the DNA outside the nucleus to the ribosome TRANSFER RNA- carries amino acids made outside the ribosome RIBOSOMAL RNA- found attached to the ribosome that helps make proteins

Major players in transcription mRNA- is made during transcription and carries the exact information from the DNA to encode for a specific protien. mRNA then travels outside the nucleus and attaches to a ribosome

TRANSCRIPTION- taking the genetic code in DNA and transferring it into RNA Process is nearly identical to replication except……. RNA forms base pairs with DNA C-G A-U

Steps in Transcription Step 1-- Helicase enzyme splits up (unzips) double stranded DNA Step 2- DNA is used as a template to make RNA Step 3- RNA polymerase attaches to specific nucleotides called PROMOTERS and begins to make a long chain Messenger RNA then stops at specific nucleotides called TERMINATION SIGNALS Step 4- used to make mRNA, tRNA, and rRNA- which will all leave the nucleus

TRANSLATION- turning the code of RNA and making it a PROTEIN—PROTEIN SYNTHESIS 2 types of RNA are needed MESSENGER RNA- long chain that has the proper CODE from the DNA TRANSFER RNA- that reads the code and attaches the proper amino acid

TRANSFER RNA Chain of RNA that has a specific shape and carries an AMINO ACID to the mRNA

CODONS and ANTICODONS Follow the “rule of threes”- reads 3 nucleotides at a time and has a specific amino acid for that codon START CODON—AUG STOP CODON---UGA, UAA, UAG

AMINO ACIDS (pg 194) the monomers for building proteins that are held together by peptide bonds (covalent bonds). There are 20 amino acids that are coded for by one or more codons (64 codons possible) AUG- the START CODON- codes for the amino acid METHIONINE UGA, UAA, and UAG- do not code for any amino acids and are considered STOP CODONS

RIBOSOMES role in translation They are the glue that holds the transfer RNA in place at the correct location on the messenger RNA. It then moves along “reading” the mRNA and adding the correct tRNA. ***** More than one RIBOSOME may be “reading” the same mRNA to speed up protein production.

ERRORS in DNA, TRANSCRIPTION or TRANSLATION MUTATIONS- any errors in the DNA or mRNA – this may or may not lead to a major change in the protein made. POINT MUTATION- a single nucleotide is inserted (paired up) incorrectly DELETION or INSERTION of a NUCLEOTIDE can lead to a FRAME SHIFT

FRAMESHIFT MUTATION The changing of all the codons due to the addition or subtraction of a nucleotide. Leads to many amino acids being changed.