DNA Replication & Protein Synthesis

Rosalind Franklin  Rosalind Franklin made a crucial contribution to the discovery of the double helix structure of DNA, but some would say she got a raw deal. 

In 1953, Watson and Crick were the scientists that proposed and built a model of DNA that we still use today!

Erwin Chargaff Discovered a relationship between the nitrogen bases. C = G

Nucleic Acids- large molecule that contain information for the cell DNA- Deoxyribonucleic acid RNA- Ribonucleic acid

Characteristics of DNA DNA is located in the nucleus Makes up genes in our chromosome Double stranded (like a twisted ladder) called a double helix

Structure of DNA- the basic unit of DNA is a nucleotide Nitrogen base phosphate Deoxyribose Structure of DNA- the basic unit of DNA is a nucleotide Consisting of THREE parts: Phosphate Five carbon sugar- deoxyribose Nitrogen base

The nitrogen bases occur in pairs: A & T- Adenine & Thymine G & C- Guanine & Cytosine

How does the DNA form a double helix? The nucleotides ( phosphate, deoxyribose sugar, nitrogenous base) join together The backbone or “sides of the ladder” are made of phosphate and sugar The middle or “steps of the ladder” are made of nitrogenous bases The nitrogen bases are held together by hydrogen bonds

The order of the bases along a strand of DNA determines or “spells out” the traits of an organism. Each group of 3 nitrogen bases are called a triplet. It spells out a specific amino acid.

Checkpoint Name 3 parts of a nucleotide. What kind of sugar is in DNA? Phosphate, Sugar, Nitrogenous base What kind of sugar is in DNA? Deoxyribose Name the 4 base pairs in DNA; Which ones bind together? Adenine & Thymine Cytosine & Guanine

DNA Replication- the process by which DNA makes an EXACT COPY of itself for the purpose of Mitosis (cell division). Replication takes place in the nucleus.

How DNA Replicates: 5 steps Helicase unwinds and unzips the DNA strand. Primase primes the DNA for replication. DNA Polymerase adds nucleotides DNA Nucleotides floating around the nucleus line up along the separated DNA strands.

How DNA Replicates: 5 steps 4. Ligase reforms the Hydrogen bonds between the nucleotides. 5. The 2 strands are proofread Two new DNA molecules are formed. They twist to form two separate double helixes (one for each nucleus!)

Leading strand 5’ to 3’ only – Follows helicase -Continuous Lagging strand – 3’ to 5’ - Okazaki fragments created and later linked together by Ligase - Discontinuous

Checkpoint What is Helicase’s job? Unzip DNA What is the difference between Leading and Lagging strands? Leading is continuous Lagging has gaps and fills backwards What is an Okazaki Fragment? Fragments of DNA in Lagging strand What are the jobs of Primase and Ligase? Primase preps DNA for replication Ligase forms Hydrogen bonds between strands

Protein Synthesis From DNA to Protein

*The complementary base pairs: A & U- adenine & uracil Characteristics of RNA *RNA is made of nucleotides with three parts Phosphate RIBOSE sugar Nitrogenous base RNA can leave the nucleus Single stranded *Four nitrogen bases: Adenine, URACIL, Guanine, and Cytosine *The complementary base pairs: A & U- adenine & uracil G & C- guanine & cytosine

RNA DNA 1. Ribose sugar 1. Deoxyribose sugar 2. Uracil (instead of thymine) 2. Thymine 3. Single stranded 3. Double stranded 4. Move in and out of nucleus 4. Does not leave the nucleus

3 types of RNA mRNA – Messenger RNA – takes message from DNA out of the nucleus tRNA – Transfer RNA – Transfers the amino acid to the Ribosome rRNA – Ribosomal RNA – helps to form ribosome

Protein synthesis is a two step process: Transcription Translation Proteins are long chains of amino acids made in cells. 20 amino acids make up all Proteins Proteins carry out the instructions that are found in the genetic code. Protein synthesis is a two step process: Transcription Translation

Transcription- messenger RNA (mRNA) codons are made from DNA template pattern. The mRNA leaves the nucleus and enters the cytoplasm. (3 steps) Initiation - Transcription begins when RNA polymerases binds to the DNA, and separates it into two strands. (TATA box) Elongation - nucleotides are added to the 3’ end of the growing RNA molecule. Termination -Transcription proceeds until the RNA polymerase reaches a termination site on the DNA (the most common stop sequence is AATAAA).  At this point, the mRNA is released.

TATA Box A TATA box is a DNA promoter sequence that indicates where a genetic sequence can be read and decoded. It specifies to other molecules where transcription begins. The TATA box is named for its conserved DNA sequence, which is most commonly TATAAA.

Intron - is any nucleotide sequence within a gene that is removed by RNA splicing. Remains in the nucleus  Exon - is any nucleotide sequence that remains after introns have been removed by RNA splicing.  May exit the nucleus.

Codon- a 3 base sequence in messenger RNA (mRNA) which is code for a specific amino acid using the mRNA Codon Chart. This codon pairs with an anticodon (mirror image) found in transfer RNA (tRNA) at the Ribosome.

Checkpoint Name the 3 types of RNA Name the 3 steps in Transcription mRNA, tRNA, and rRNA Name the 3 steps in Transcription Initiation, elongation, and termination Name the 4 bases in RNA Adenine, Cytosine, Guanine, and Urasil In what type of RNA would find a codon? mRNA In what type of RNA would find an anticodon? tRNA

Translation- amino acids which make up proteins are assembled through the direction of the mRNA and the tRNA. A tRNA anticodon pairs with the mRNA codon. The tRNA is carrying (or transferring) an amino acid. A peptide bond forms between each amino acid and forms a protein.

Checkpoint Draw steps from DNA to Protein DNA mRNA Protein Transcription Translation Name the bond formed between the amino acids. Peptide Bond

MUTATIONS

Genetic Changes Mutations- mistakes…they happen! : ( Repair enzymes travel up and down the DNA looking for problems. Sometimes they can be repaired. If the mistake is not repaired, a MUTATION occurs. Some mutations are helpful (evolution), some are harmful (cancer), and some make no difference in the organism.

Point Mutations- a change in a single base pair of DNA. The cat ate the rat. The car ate the rat. The t was changed for r Frameshift Mutations- a mutation that shifts the reading of codons *Deletion- a single base is DELETED The cat ate the rat The ata tet her at. The c was deleted *Duplication- a single base is DUPLICATED The cat ate the rat. The eca tat eth era. The e was duplicated *Insertion- a single base INSERTED for another base The cat aat eth era. The a was inserted

Translocation Mutations Chromosome mutations in which chromosome segments, and the genes they contain, change positions. Translocations can occur within a chromosome (intrachromosomal) or between chromosomes (interchromosomal).

An inversion is a chromosome rearrangement in which a segment of a chromosome is reversed end to end. An inversion occurs when a single chromosome undergoes breakage and rearrangement within itself.

Silent mutations are DNA mutations that do not significantly alter the phenotype of the organism in which they occur. Silent mutations can occur in non-coding regions (outside of genes within introns), or they may occur within exons. When they occur within exons they either do not result in a change to the amino acid sequence of a protein, or result in the insertion of an alternative amino acid with similar properties to that of the original amino acid, and in either case there is no significant change in phenotype

A missense mutation is a point mutation in which a single nucleotide change results in a codon that codes for a different amino acid. A nonsense mutation is a point mutation in a sequence of DNA that results in a premature stop codon, or a nonsense codon in the transcribed mRNA, and in a truncated, incomplete, and usually nonfunctional protein product.

A mutagen is a physical or chemical agent that changes the genetic material, usually DNA, of an organism and thus increases the frequency of mutations. As many mutations cause cancer, mutagens are therefore also likely to be carcinogens.

Checkpoint Type of mutation that has no effect on the organism. Silent mutation Name the mutation that is a change in a single base pair. Point mutation True or False: All mutations are harmful? False Name the 3 types of frameshift mutations Insertion, Deletion, Duplication