DNA Structure DNA: deoxyribose nucleic acid nucleic acidOne of the 4 macromolecules (nucleic acid) Polymer of nucleotides

DNA Structure

Nucleotide: subunits of nucleic acids

Molecular Genetics DNA Structure  Nucleotides  Consist of a five-carbon sugar, a phosphate group, and a nitrogenous base 12.1 DNA: The Genetic Material Chapter 12

DNA is made up of 4 different nitrogenous bases: Adenine (A) Cytosine (C) Guanine (G) Thymine (T)

Purine bases: A and G Pyrimidine bases: C and T

Chargaff’s Rule: A always bonds with T and G always bonds with C

Weak hydrogen bonds hold bases together

Molecular Genetics Chargaff  Chargaff’s rule: C = G and T = A 12.1 DNA: The Genetic Material Chapter 12

What do you notice about different species nucleotides?

Molecular Genetics 12.1 DNA: The Genetic Material When the nucleotides bond together, DNA forms a double helix Chapter 12

DNA Structure DNA looks like a twisted ladder Sides of the ladder —alternating deoxyribose (sugar) and phosphate groups Steps of the ladder —complimentary nitrogenous bases (cytosine–guanine or thymine–adenine)

Two scientists, Watson and Crick, are build the double helix model

Molecular Genetics Watson and Crick  Built a model of the double helix that conformed to the others’ research 1. two outside strands consist of alternating deoxyribose and phosphate 2. cytosine and guanine bases pair to each other by three hydrogen bonds 3. thymine and adenine bases pair to each other by two hydrogen bonds 12.1 DNA: The Genetic Material Chapter 12

12.1 DNA: The Genetic Material Molecular Genetics Chromosome Structure  DNA coils around histones (proteins) to form nucleosomes  Nucleosomes package and fold the DNA into chromatin fibers  The chromatin fibers supercoil to form chromosomes that are visible in the metaphase stage of mitosis Chapter 12

12.2 Replication of DNA Molecular Genetics Semiconservative Replication  Parental strands of DNA separate, serve as templates, and produce DNA molecules that have one strand of parental DNA and one strand of new DNA. Chapter 12

Molecular Genetics Unwinding  An enzyme, DNA helicase, is responsible for unwinding and unzipping the double helix Replication of DNA Chapter 12

Bases are exposed “Free” nucleotides found in the nucleus bond to their complimentary bases of both strands (A to T and C to G) Two new identical molecules of DNA are formed

Each new cell gets a copy of the DNA

This occurs during interphase!!

Molecular Genetics  One strand is called the leading strand and is elongated as the DNA unwinds.  DNA polymerase attaches nucleotides to the leading strand  The other strand of DNA, called the lagging strand, elongates away from the replication fork Replication of DNA Chapter 12

Central Dogma of Biology

What’s the Big Deal about DNA? DNA codes for RNA which guides the synthesis of proteins Remember, proteins are the building blocks of cells

RNA: ribonucleic acid Nucleic acid The principle molecule that carries out the instructions coded in DNA

RNA

RNA differs from DNA in 3 ways:

The sugar in RNA is ribose, not deoxyribose

It is single stranded

Contains the base uracil instead of thymine (U bonds with A)

Molecular Genetics Messenger RNA (mRNA)  Long strands of RNA nucleotides that are formed complementary to one strand of DNA 12.3 DNA, RNA, and Protein Chapter 12

Transfer RNA (tRNA) Smaller segments of RNA nucleotides that transport amino acids to the ribosome

 Ribosomal RNA (rRNA)  Associates with proteins to form ribosomes in the cytoplasm, contain no genetic info.

Transcription Transcription: process by which RNA is made Part of the nucleotide sequence of a DNA molecule is copied into RNA Occurs in the nucleus

Steps of Transcription DNA is unzipped in the nucleus by an enzyme Another enzyme, RNA polymerase, bonds “free nucleotides” to the exposed bases

Adenine bonds with uracil (A to U) and guanine bonds to cytosine This chain is called mRNA

Consists of multiple codons

Codon: group of 3 nucleotides in mRNA that specify one amino acid Ex. AAA CAC GGU reads as 3 codons AAA codes for the amino acid lysine CAC codes for the amino acid histidine

Molecular Genetics 12.3 DNA, RNA, and Protein Chapter 12

Suppose the DNA strand is CGT-ACG- AAA, what is the mRNA strand? 20 different amino acids make up proteins

Translation Translation: nucleotides in mRNA are decoded into a sequence of amino acids in a protein Occurs after transcription in the cytoplasm Involves the ribosomes

Steps of Translation mRNA leaves the nucleus and attaches to the ribosomes, where it acts as a pattern to line up amino acids –Each triplet codon codes for an amino acid

The ribosome reads each triplet codon (on the mRNA)

Transfer RNA (tRNA) brings amino acids to the complementary codon on the mRNA –This is called the anti-condon

The ribosome bonds the amino acid to the previous amino acid tRNA moves off into the cytoplasm to pick up another amino acid

Amino acids are scattered throughout the cytoplasm

Each tRNA can only deliver one type of amino acid When the protein is assembled, the mRNA breaks up and becomes free nucleotides again A stop codon releases the polypeptide (protein)

Molecular Genetics 12.3 DNA, RNA, and Protein Chapter 12

Molecular Genetics Mutations  A permanent change that occurs in a cell’s DNA is called a mutation.  Types of mutations  Point mutation  Insertion  Deletion  Duplication 12.4 Gene Regulation and Mutation Chapter 12

Point Mutation A chemical change in one base pair

Substitution Substitution: When one base is exchanged for another

Missense: DNA code is altered and codes for the wrong amino acid

–Nonsense: change the codon for the amino acid to a stop codon

Insertion Addition of nucleotide in the DNA sequence

Deletion Loss of a nucleotide in the DNA sequence

Both insertion mutations and deletion mutations change the multiples of 3 from the point of insertion or deletion Frameshift mutations

Duplication A DNA codon is duplicated in the DNA sequence

Molecular Genetics 12.4 Gene Regulation and Mutation Chapter 12

Molecular Genetics Causes of Mutation  Can occur spontaneously  Chemicals and radiation also can damage DNA.  High-energy forms of radiation, such as X rays and gamma rays, are highly mutagenic Gene Regulation and Mutation Chapter 12

Some mutations have no effect on an organism’s phenotype others can be lethal

Cancer: the unrestrained growth of cells Exposure to radiation and certain chemicals increases the chance of cancer Usually caused by mutations found in specific genes (oncogenes)

Molecular Genetics Body-cell v. Sex-cell Mutation  Somatic cell mutations are not passed on to the next generation.  Mutations that occur in sex cells are passed on to the organism’s offspring and will be present in every cell of the offspring Gene Regulation and Mutation Chapter 12

Sequence of Events 1.DNA molecule starts replication process –Helicase opens up molecule 2.DNA molecule replicates –Leading strand synthesized easily –Lagging strand synthesis is more difficult 3.New DNA molecules are produced. –Molecules are mirror images of parent strand

Sequence of Events 4. RNA Polymerase opens DNA molecule to synthesize mRNA strand –Uracil replaces Thymine 5. mRNA molecule leaves nucleus and enters cytoplasm –This is crucial, considering DNA cannot leave the nucleus on its own

Sequence of Events 6. mRNA molecule finds Ribosome 7. tRNA matches mRNA and brings along with it the amino acids

Sequence of Events 8. Methionine is first amino acid in the resulting chain 9. A stop codon will be the last in the chain 10. Once synthesis of the amino acid chain is completed, the protein is able to be used by the body

Genetic Mutations Point Mutation - change in one base of the gene sequence –Original: The fat cat ate the wee rat. –Point Mutation: The fat hat ate the wee rat. Frame Shift Mutation - one or more bases are inserted or deleted, the equivalent of adding or removing letters in a sentence –Original: The fat cat ate the wee rat. –Frame Shift: The fat caa tet hew eer at.

Genetic Mutations Deletion - Mutations that result in missing DNA –Original: The fat cat ate the wee rat. –Deletion: The fat ate the wee rat. Insertion - Mutations that result in the addition of extra DNA –Original: The fat cat ate the wee rat. –Insertion: The fat cat xlw ate the wee rat.

Genetic Mutations Inversion - an entire section of DNA is reversed –Original: The fat cat ate the wee rat. –Insertion: The fat tar eew eht eta tac. NEW TYPE

Missense and Nonsense Missense – single nucleotide is changed resulting in a different amino acid Nonsense – point mutation that results in a premature stop codon Silent – change in nucleotide, however no change in amino acid takes place