DNA & RNA Biology Chapter 12 & 13

Identifying the DNA Frederick Griffith in 1928 while searching for a cure for Steptococcus pneumniae discovered transformation. (the ability to pass & change one trait from organism’s gene to another). Oswald Avery demonstrated nucleic acid DNA was responsible for the change, it stores and transmits the genetic information from one generation to another. Hershey and Chase used T4-bacteriophage (virus that infects bacteria, which mean “bacteria eater”) to demonstrate DNA. They concluded the genetic material for a bacteriophage was DNA not a protein.

Structure of DNA DNA is made of subunits called nucleotides that form a long chain. Nucleotide has three parts: a phosphate group, a 5-carbon sugar (deoxyribose) molecule and a nitrogen base Sugar and phosphate are the same for each nucleotide. Nitrogen bases are one of four: purines have 2-rings:-adenine and guanine, & pyrimidines have 1-ring: thymine and cytosine A-T & C-G pair to form the double helix

DNA structure Double Helix: Watson and Crick developed the model of DNA, held together with hydrogen bonds

Central Dogma of Genetics The “central dogma” is a roadmap of how information within the DNA is transferred to protein, the building blocks of your body. Replication Transcription Translation Protein DNA RNA

DNA Replication The process of making a new strand of DNA is called replication. Enzymes (DNA polymerase)work to unwind and separate the double helix and add complimentary bases ( they “un-zip the double helix). DNA polymerases has a proof reading role which makes sure each strand is correct. Two new double helixes of DNA are created from one double helix strand by adding a complimentary strand to the unzipped part (the template & follow base rules). Therefore every new double helix of DNA contains one strand from the original which acts as a template and new one.

DNA Replication Prokaryote: usually begins at a single point & proceeds in two directions until the entire chromosome is copied Eukaryote: Replication may begin at dozens or hundreds of locations & proceed in both directions until each chromosome is completely copied

DNA Replication Double helix is unzipped Base pair occurs on each template (original strand 2-new strands form Each strand has same sequence produced 2 new identical strands (double helix).

RNA Primary function is protein synthesis Each type of RNA has a specialized role

RNA-Ribonucleic acid Similar to DNA in that it is made up of nucleotides with a 5-carbon sugar r, a phosphate group, and a nitrogenous base. 3-main differences A-RNA 5-carbon sugar is ribose B- 3 of the bases are the same Adenine, Cytosine and Guanine. RNA does not have Thymine instead it has Uracil (U). C-RNA is usually single-stranded and can leave the nucleus.

RNA vs DNA

RNA-Ribonucleic acid RNA is present in cells in three different forms. Messenger RNA (mRNA) ;Ribosomal RNA (rRNA); Transfer RNA (tRNA) All three are necessary to process information from DNA into proteins (gene expression) Gene expression occurs in two stages transcription: info in DNA is transferred to mRNA; translation: info in mRNA is used to make a protein.

RNA mRNA-messenger RNA copied from a single strand of DNA carry the instructions for assembling amino acids out of nucleus. rRNA-ribosomal RNA makes up the major part of ribosome copied from mRNA (use base rules) tRNA-transfer RNA responsible for transferring each amino acid to the ribosome(s) its coded specifically for during protein synthesis

mRNA mRNA is coded from DNA transcription

rRNA rRNA is derived from mRNA

tRNA

Transcription Transcription is the copying of info from a nucleotide sequence of DNA into a complimentary strand of RNA. It requires a RNA polymerase to bind with the DNA after it separates the DNA strand; the RNA polymerase will then use one strand of DNA as a template from which nucleotides form into a strand of RNA (mRNA) Transcription creates a partial copy of the DNA as mRNA rRNA tRNA.

Transcription The new mRNA strand is not a copy of the whole DNA strand, but only contains info about one gene. DNA fragment is being transcribed can be divided into three regions.. Promotor-tells the RNA polymerase when to start The part which is being transcribed. Terminators-tells the RNA polymerase when to stop

Structure of a Gene Genes are the DNA-encoded information that specifies particular proteins; each gene is made of a specific sequence of nucleotides. If code is not present the trait will not appear. Genes have nucleotides with no coding sequence called introns. Nucleotide that codes amino acids are exons Multigene families contain versions of the same gene.

Gene Expression An organism’s traits are determined by proteins that are built according to the plans specified in its DNA. How does DNA determine the nature of a protein. The working instructions of the genes are made of molecules of RNA. RNA is single strand of nucleotides. RNA contains the sugar ribose. RNA has a nitrogen-containing base called uracil.

Translation Translation is the synthesis of proteins and takes place in the ribosomes. Every three sequences in mRNA are called codons. A Codon is one gene. Each codon represents a different amino acid. These amino acids are brought to the ribosomes by tRNA and hooked up together to form a protein. tRNA has a start coden (AUG) and stop coden (TAA, TAG, TGA)

Genetic Code The instructions for building a protein are written as a series of three-nucleotide sequences called codons. Proteins make up the traits in your body 64 different possible codons

Transcription DNA strands are separated RNA polymerase then uses one strand of DNA as a template to form a strand of RNA RNA knows where to begin “reading” by a promoter segment and signals where to read “transcription” and when to stop “reading”. RNA edits some material “introns” from DNA material not involved in protein synthesis and “exons” DNA which codes for protein which are expressed.

Genetic Codes Proteins are made by joining amino acids into long chains called polypeptides. RNA carries 4 different bases G-C-A-U in various combinations, each genetic code is read in segments of 3 letters; the 3-letter word in mRNA is called a codon (this specifies a single amino acid) GAA/CCC/ACG/UGA Since there are 4 different bases there are 64 possible 3 base combinations: 4x4x4=64

Translation The sequence in a mRNA molecule serves as instruction for the order in which the amino acids should be joined together. In the cell the ribosomes “read” the instructions of the polypeptide; this “reading” or decoding of mRNA is called Translation.

Mutations Mutations are changes in the genetic material Two main types : Gene mutations changes in 1 or a few nucleotide; ex: insertion or deletion-more dramatic can completely shift the reading of the codons these types of changes are reffered to as fameshift mutations; substitution-usually affects only 1 amino acid. Look on page 307

Chromosomal mutations Changes in the number or structure of chromosomes. Page 308 figure 12-21 Deletion, loss of all or part of a chromosome Duplication produce extra copy(ies) of part or all of chromosome. Inversion reverse the directions of the chromosome. Translocation when part of one chromosome breaks off and attaches to another.

Mutation Cri-du-Chat (cats cry)occurs when the P-arm (upper arm is missing some genes)

Gene Regulation Operon-groups of genes that operate together in prokaryotes Ekaryotes- use the “TATA box” a group of sequence base pairs either TATATA or TATAAA to begin “reading”

Mutations Heritable changes in genetic information Two basic categories: single gene mutations called point mutation- substitution / insertion / deletion {also called frame shift} Chromosomal mutation, changes in number and structure of the chromosome may be caused by natural events or artificial factors such as mutagens