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Part 1 - DNA Replication Part 2 - Transcription and Translation. DNA Replication. The Eukaryotic Cell Cycle – DNA Replication has to happen before the cell can divide so Both CELLS HAVE DNA.
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The Eukaryotic Cell Cycle – DNA Replication has to happen before the cell can divide so Both CELLS HAVE DNA.
THINK ABOUT ITBefore a cell divides, its DNA must first be copied.How might the double-helix structure of DNA make that possible?
If the sequence of one strand is known, the other strand is known A T C G G C T A T C G A T A G C C G A T A G C T
DNA Replication The structure of DNA explains how it replicates DNA “unzips” down the middle Free floating nucleotides pair up with both sides of the DNA molecule ATCGA TAGCT ATCGA TAGCT ATCGA TAGCT ATCGA TAGCT Original Exactly Copied DNA Strands
DNA Replication This process produces two exact DNA molecules (Chromosomes) that are the same DNA never leaves the nucleus
The Role of Enzymes • How does this happen?? • DNA replication is carried out by a series of enzymes. • They first “unzip” a molecule of DNA by breaking the hydrogen bonds between base pairs.
The Role of Enzymes • - DNA Polymerase • - DNA polymerase is an enzyme that joins individual nucleotides to produce a new strand of DNA. • - DNA polymerase also “proofreads”
Replication in Living Cells • How does DNA replication differ in prokaryotic cells and eukaryotic cells? • Replication in most prokaryotic cells starts from a single point and proceeds in two directions until the entire chromosome is copied.
Replication in Living Cells • How does DNA replication differ in prokaryotic cells and eukaryotic cells? • In eukaryotic cells, replication may begin at dozens or even hundreds of places on the DNA molecule, proceeding in both directions until each chromosome is completely copied.
Transcription And Translation
DNA Works as a Code Codon- a three nucleotide sequence that codes for a single amino acid With 4 different types of nucleotides in triplet codes, 64 combinations are possible • 61 of the codons code for 20 amino acids • 3 codons signal a stop- Identifies the end of a protein The genetic code is exact. If a sequence of DNA is known, the resulting amino acid chain (protein) is known
If DNA never leaves the nucleus, how can the DNA message get to the site of protein production, the ribosome?
Answer: The DNA message is copied to RNA during the process of Transcription
The Structure of RNA • RNA is single stranded • The sugar in RNA is Ribose, not deoxyribose as in DNA • The DNA nucleotide thymine is replaced by the RNA nucleotide Uracil
RNA’s Functions: Two Types, Two Jobs • m-RNA(messenger RNA) delivers the copied DNA from the nucleus to the Ribosome- the site of protein synthesis • t-RNA(transfer RNA) picks up specific amino acids in the cytoplasm and delivers them to the ribosome
Steps in Protein Synthesis • DNA molecule unzip where the desired gene is located • Free floating RNA nucleotides pair with the DNA strand forming m-RNA (Transcription) • The m-RNA leaves the nucleus and goes to a ribosome • A specific t-RNA delivers a specific amino acid to the ribosome (Translation) • The m-RNA codon matches with the t-RNA anticodon bringing the amino acid into its proper place • When the next amino acid is in place, the two are joined in a condensation reaction • The process is repeated until a stop code is read and a complete protein is formed
Mutation- change in the genetic code 1. Gene Mutation or Point Mutation- a nucleotide base is added, subtracted or changed to produce a change in the amino acid sequence of a protein
A change in a single base in the DNA strand will result in a change in the m-RNA strand and the resulting protein Normal Hemoglobin Amino Acids DNA RNA 5 6 7 GGA CTC CTC CCU GAG GAG Proline Glutamic Acid Glutamic Acid Sickle Cell Hemoglobin Proline Valine Glutamic Acid GGA CAC CTC CCU GUG GAG
Chromosome Mutation- involves a change in many genes a) Deletion- part of a chromosome is lost b) Inversion- part of a chromosome is flipped around c) Translocation- part of a chromosome is added to another chromosome
Somatic & Germ Mutations a) Somatic mutations: change that occurs in body cells. Affects only the individual. Ie. cancer b) Germ Mutations- changed in the genetic code of gametes that will affect the individuals offspring Mutagens- substances capable of causing damage to DNA Most mutations are harmful
Frame Shift Mutations • An insertion or deletion that results in the reading frame being shifted. • All codons following the mutation will be changed. • Example: THE RED DOG ATE THE CAT HER EDD OGA TET HEC AT