Notes: DNA & RNA DNA Characteristics DNA Replication RNA Characteristics Transcription Translation Genetic Mutations

Make sure you have completed the timeline at the front of your DNA/RNA Notes All of these people should be included (use textbook – CH 12): James Watson & Francis Crick Alfred Hershey & Martha Chase Fredrick Griffith Oswald Avery Rosalind Franklin Erwin Chargraff These People will be on your TEST!!!

What is DNA? Your “genetic” information (GENES) Deoxyribonucleic acid The monomer of DNA is a nucleotide  many nucleotides join to form a long chain of DNA . Nucleotides have 3 parts: Phosphate Sugar (Deoxyribose) Nitrogenous base

DNA Structure: What does DNA look Like? Classic “Double Helix” Shape Two sides of DNA are ANTI – PARALLEL  parallel but go in different directions Must be in this shape so DNA can be compacted and fit inside of structures called Chromosomes. Remember you have 46 Chromosomes…. Each with SAME TYPE of DNA. DNA, and chromosomes, are found in the NUCLEUS – the control center of the cell!

DNA Structure: What does DNA look Like? (continued…) The backbone /sides of the “ladder” are made up of alternating Sugars (Deoxyribose) & Phosphates. The “steps” or rungs of the “ladder” are made of 4 major Nitrogenous Bases: Adenine 3. Cytosine Thymine 4. Guanine When looking at the Nitrogen Bases…. A always pairs with T G always pairs with C

The Nitrogen bases are held together by weak covalent bonds called Hydrogen Bonds (Remember those from our discussion on water?) 2 Groups of Bases: Purines (double-ringed structure) -Adenine -Guanine Pyrimidines (single-ringed structure) -Thymine -Cytosine Phosphate Deoxyribose

DNA Replication: Why Replicate? In preparation for cell division (during the S Phase of Interphase), a cell must duplicate its genetic info (DNA) to pass on to the new daughter cells.

How does Replication Work? DNA must first be “untwisted” and “unzipped.” The enzyme helicase “unzips” the DNA strand – at the hydrogen bonds. A replication fork is formed. Each DNA Strand acts as a template for the NEW strand to be formed

DNA polymerase (enzyme/protein) binds to the DNA strand DNA polymerase (enzyme/protein) binds to the DNA strand. adds complimentary nitrogen base pairs to the un-matched nitrogen base pairs in the 5”  3” direction As the polymerase moves along the DNA it constructs a new strand that matches each of the old strands. Matches the nucleotides A – T and G – C.

The result is 2 new identical DNA molecules – one from the parent strand and one new strand. DNA Polymerase remains attached until 2 new DNA strands are created; it “proofreads” the strands to minimize error in the process

RNA Ribonucleic Acid How is RNA different from DNA??? Has a RIBOSE instead of a deoxyribose (sugar backbone) Single Stranded…Not double stranded Contains URACIL( U ) instead of Thymine (T) A binds with U; G binds with C RNA Nucleotide consists of… Sugar (Ribose) Phosphate Nitrogen Base (A, U, G, or C)

The 3 types of RNA mRNA = (messenger) codes for polypeptides rRNA = (ribosomal) makes up ribosomes. RIBOSOMES are the protein builders!!! tRNA = (transfer) brings the amino acids to the ribosome during protein synthesis

Different types of RNA…

RNA Section 3 Parts of Nucleotide: mRNA/ rRNA/ tRNA Ribose (instead of deoxyribose) Single Stranded (instead of double stranded) Uracil (No thymine) 3 Parts of Nucleotide: Ribose (sugar) Phosphate Nitrogen Base (A, U, G, or C) mRNA/ rRNA/ tRNA

mRNA Section rRNA Section Messenger RNA Carries message/ instructions from DNA to Ribosomes Made in the Nucleus Codon = 3 nucleotides/ nitrogen base pairs put together that code for an amino acid rRNA Section Ribosomal RNA Genetic info of ribosome ; builds polypeptides Ribosome Proteins

tRNA Section Transfer RNA Transport Amino Acids to Polypeptide Chain Found in Cytoplasm Anticodon – 3 matching nucleotides that allow tRNA to attach to a codon

2 Stages in making proteins Transcription – using DNA template to make mRNA strand Translation – using mRNA strand to create polypeptides

Transcription: DNA  mRNA This is the process by which mRNA is produced/written (transcribed) from DNA. This process occurs in the nucleus, because DNA is TOO LARGE to leave the nucleus.

The Major Steps of Transcription DNA gets unzipped by RNA polymerase. The RNA polymerase reads along one DNA strand and uses it as a template, reading one codon at a time. Codons are groups of 3 nucleotides that code for a specific amino acid. You can think of codons as “words” in a sentence. Each nitrogen base = a letter; each codon (which are made of nitrogen bases) = a word; each codon (or word) means something in the mRNA sentence…the codons/ words code for an Amino Acid!!!! “Start” codon = AUG (Methionine) “Stop” codons = UAA, UAG, and UGA

mRNA is produced/ transcribed with the complimentary nucleotides. The polymerase keeps making the mRNA until a “stop” codon is reached. When the “stop” is reached, the new strand of mRNA breaks away, leaves the nucleus through the nuclear pore, and travels to the RIBOSOME. This is where protein synthesis begins. The next major process of translation will occur at the ribosome, in the cytoplasm of the cell.

Example (Look under step #2) U-C-A-U-G-G-G-C-A-C-A-U-G-C-U-U-U-U-G-A-G methionine glycine threonine cysteine phenylalanine STOP  

Translation: mRNA  rRNA & tRNA  PROTEIN (polypeptides) The synthesis of polypeptides (PROTEINS) by the ribosome using the message carried by the mRNA

Steps of Translation The ribosome attaches to the first codon of mRNA. A tRNA anticodon matches up to the first codon on the mRNA – this is always AUG “start” An anticodon is the complimentary base pair that matches the codon. For example, if the codon is GGA, the anticodon is CCU. The tRNA is carrying an amino acid. The ribosome (rRNA) pulls the mRNA through and reads the next codon and matches up the correct tRNA; bringing the next amino acid into line.

The ribosome binds the first and second amino acids together. The tRNA’s leave after they “drop off” the amino acids. This process occurs over and over until a stop codon is met. The result is a chain of polypeptides  PROTEIN.

So…How does all this DNA stuff fit together??? Amino acids (aa)  Polypeptides  Proteins There are 20 different amino acids.   Question: “What is a gene?” Answer: “A particular segment of DNA that code for one particular protein.”

Mutations Genetic Mutations are any defect or change in genes (DNA) There are 2 Types of Mutations: Gene Mutations Chromomosome Mutations

Gene Mutations Changes in nucleotides. Point Mutations Nitrogen Base Pair Changes Examples include: Substitution  wrong base pair (bp) Insertion  enter wrong bp Deletion  remove wrong bp Point mutations are the substitution, addition, or removal of a SINGLE nucleotide / N2 Base

Examples of Gene/ Point Mutations Frameshift Mutations: types of point mutations that shift the “reading frame” of the genetic message (usually a result of an insertion or deletion)

Chromosome Mutations changes in # or structure of chromosome Deletion  missing chromosome Duplication  extra chromosome Inversion backwards/ reversed chromosome Translocation chromosome moved to different location

The proteins formed by translation are responsible for all of our traits! So what controls how genes are turned ON or OFF? Gene Regulation is controlled by a group of genes that operate together called OPERONS. Many times these genes must work together, in order to control a function. Example Ecoli and the Lac Operon. Lactose is a SUGAR (carbohydrate) that can be broken down into GLUCOSE + GALACTOSE.

When Ecoli, is placed in a medium where it is forced to eat ONLY lactose, it must be able to breakdown lactose into these two substances. If Ecoli is placed in a medium that DOES NOT contain LACTOSE, it does not need to transcribe (or read) those genes… So it does not read those genes. LAC GENES are turned OFF by REPRESSORS and turned ON by LACTOSE!!!

The repressor protein is always present on the genes of Ecoli The repressor protein is always present on the genes of Ecoli. It is bound to the OPERATOR  the section of DNA that surrounds the area where the genes for breaking down lactose are located. The only way for RNA POLYMERASE to transcribe these genes, is if the repressor protein is moved . To do this, lactose will bind to the lac repressor and move the repressor protein away = RNA Transcription!!!

MOST EUKARYOTIC GENES are controlled individually and have regulatory sequences that are much MORE COMPLEX than those of the lac operon in bacteria. Hox genes  genes within eukaryotic cells that control the organs and tissues that develop in various parts of an embryo. Mutations in these genes can completely change the organs that develop in specific parts of the body!! EXAMPLE: Drosophilia (common fly) replacing their antennae with LEGS growing out of their heads!!!!