DNA Deoxyribonucleic Acid Composition A nucleic acid made

DNA �Deoxyribonucleic Acid

Composition � A nucleic acid made up of monomers nucleotides

Recall: Nucleotides are made of �A phosphate group �A nitrogenous base �A 5 -carbon sugar deoxyribose

4 Different Nitrogenous bases Make Up DNA � Adenine A � Cytosine C � Guanine G � Thymine T

Forming the Double Helix �Composed of sugar-phosphate strands ( two of them) �Strands are held together by hydrogen bonds

�hydrogen Base-Pairing bonds could create a nearly perfect fit between nitrogenous bases along the center of the molecule. �This fit between A–T and G–C nucleotides is known as base pairing.

DNA Replication � Process through which DNA is copied or duplicated � This happens during the Synthesis Phase (S phase) of the cell cycle

�Occurs to copy the genetic information from one cell to another �Enzymes separate the two strands from the double helix and then “synthesize” two new strands in order to get two complete copies of the double helix.

• Because each strand can be used to make the other strand, the strands are said to be complementary.

�DNA replication results in two DNA molecules each with one new strand one original strand

The role of enzymes �DNA polymerase is an enzyme that joins individual nucleotides to produce a new strand of DNA. � DNA polymerase also “proofreads” each new DNA strand, ensuring that each molecule is a perfect copy of the original.

RNA

RNA � Ribonucleic acid � Principle molecule that carries out the instructions coded in DNA

� � � RNA vs. DNA 1. RNA contains ribose instead of deoxyribose like DNA. 2. RNA contains uracil instead of thymine 3. RNA is a single strand instead of double-stranded. RNA is complementary to one DNA strand.

�The three main types of RNA are messenger RNA (m. RNA), ribosomal RNA (r. RNA), and transfer RNA (t. RNA).

Transcription During transcription, segments of DNA serve as templates to produce complementary m. RNA molecules. � The base sequences of the transcribed RNA complement the base sequences of the template DNA.

�. RNA Polymerase � RNA polymerase binds to DNA during transcription and separates the DNA strands. � RNA polymerase then uses one strand of DNA as a template from which to assemble nucleotides into a complementary strand of m. RNA.

Genetic Code �The sequence of amino acids that give a person his or her genetic information.

� The specific amino acids in a polypeptide, and the order in which they are joined, determine the properties of different proteins. � The sequence of amino acids influences the shape of the protein, which in turn determines its function.

�Each three-letter “word” in m. RNA is known as a codon. �A codon consists of three consecutive bases that specify a single amino acid to be added to the polypeptide chain.

� Ribosomes use the sequence of codons in m. RNA to assemble amino acids into polypeptide chains. � The decoding of an m. RNA message into a protein is a process known as translation.

� Translation begins when a ribosome attaches to m. RNA � the ribosome reads each codon of m. RNA, and directs t. RNA to bring the specified amino acid to the ribosome. � the ribosome attaches each amino acid to the growing chain.

�What is the “central dogma” of molecular biology? The central dogma of molecular biology is that information is transferred from DNA to RNA to protein. �

� One of the most interesting discoveries of molecular biology is the near-universal nature of the genetic code. � Despite their enormous diversity in form and function, living organisms display remarkable unity at life’s most basic level, the molecular biology of the gene.

MUTATIONS

Types of Mutations � 1. Gene Mutations �produce � changes in a single gene 2. Chromosomal Mutations �produce changes in whole chromosomes

Gene Mutations � Mutations that involve changes in one or a few nucleotides are known as point mutations because they occur at a single point in the DNA sequence. They generally occur during replication.

Point Mutations • Point mutations include substitutions, insertions, deletions, silent, missense and nonsense mutations.

Substitutions In a substitution, one base is changed to a different base. � Substitutions usually affect no more than a single amino acid- missense, and sometimes they have no effect at all-silent. �

� Insertions and deletions are called frameshift mutations because they shift the “reading frame” of the genetic message. Frameshift mutations can change every amino acid that follows the point of the mutation and can alter a protein so much that it is unable to perform its normal functions.

Silent Mutations � � A mutation that does not change the resulting protein. Does not change the amino acid sequence

Missense Mutation � � Change one amino acid in the resulting protein The “meaning” of one codon changes

Nonsense Mutation � A stop codon is inserted and shortens the resulting protein

Types of Chromosomal Mutations � Deletion � Duplication � Inversion � Translocation

Deletion � Deletion involves the loss of all or part of a chromosome.

Duplication � Duplication produces an extra copy of all or part of a chromosome.

Inversion � Inversion reverses the direction of parts of a chromosome.

Translocation � Translocation occurs when part of one chromosome breaks off and attaches to another.

Effects of Mutations � How � The do mutations affect genes? effects of mutations on genes vary widely. Some have little or no effect; and some produce beneficial variations. Some negatively disrupt gene function.