DNA_ RNA_ _ PROTEIN SYNTHESIS

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					DNA, RNA, & PROTEIN SYNTHESIS
UNDERSTANDING THE STRUCTURE & FUNCTION OF GENETIC INFORMATION

The Big Picture
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Nucleotides  DNA  Genes  Chromosomes Sections of DNA are called genes Genes come in different forms called alleles Each allele codes for a specific protein that causes a trait

Genes

3 Critical Things
 Genes MUST be able to do three critical things:
 Carry information from one generation to the next (process of Meiosis)  Put genetic information to work controlling traits (process of Protein synthesis)  Be easily copied when cells replicate (S phase of interphase & DNA replication)

Nucleotide Review
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 

Nucleotides are the monomers of nucleic acids contain elements CHOPN located in DNA, RNA, and freely floating in nuclear cytoplasm

3 parts of a Nucleotide
 Pentose sugar: Deoxyribose or Ribose  Phosphate group  Nitrogenous base

Nitrogenous Bases

Deoxyribonucleic Acid
 Coiled double helix (2 strands) – like a ladder

DNA
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Sides made of sugar Ribose attached to phosphate groups Rungs/steps made of nitrogenous bases held together by hydrogen bonds

DNA
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Contains bases adenine, thymine, guanine, cytosine DNA and proteins make up chromatin  chromatin coils to form a chromosome during DNA replication and cell division

DNA Structure

DNA Location
 Location: stays contained in the nucleus except during cell division  One human DNA molecule is 4 cm.  There are 2 meters of DNA in a cell’s nucleus

DNA

DNA Function
 Stores genetic information  Controls cell activities by transmitting instructions for making proteins  Replicates itself during mitosis

History of DNA Discovery
 SUTTON (pic)
 1902  Discovered DNA in chromosomes

 LEVENE
 1920’s  Determined 3 parts of nucleotide

History of DNA Discovery
 AVERY, MCCARTY, MCLEOD
 1944  it was DNA that transmitted genetic info from 1 generation to another

History of DNA Discovery
 FRANKLIN & WILKINS
 Early 1950’s  Used X-rays that determined spacing of nucleotides and twisted structure

Rosalind Franklin

History of DNA Discovery
 WATSON & CRICK
 1953  Worked out structure and chemical composition of DNA by using other scientists’ results – built first model of DNA

Watson & Crick

DNA Replication
 Purpose: to make an exact copy of the DNA during the S phase of interphase

Steps in DNA Replication
 DNA helicase breaks H bonds between nitrogen bases causing complementary strands to “unzip” and separate

Complementary Strands
 Each complementary strand serves as a template (pattern) for the new strands to form DNA polymerase adds new nucleotides to the exposed bases



Complementary Base Pairing
 Complementary base pairing  A only bonds to T  C only bonds to G

Complementary Base Pairing

Phosphodiester bonds
 This process continues until the strands are replicated

Completion
 DNA polymerase also “proofreads” the new DNA for errors and performs an excision repair if needed.  DNA helicase recoils the two new identical DNA molecules  Triplet: a 3-base sequence of DNA

RNA and Protein Synthesis

Comparison of RNA to DNA
Characteristic DNA RNA

Major cellular site
Major function

Nucleus
Directs protein synthesis Deoxyribose

Cytoplasm outside nucleus
Carries out protein synthesis Ribose

Sugar

Comparison of RNA to DNA
Characteristic DNA RNA

Nitrogenous bases

Structure

Adenine, Guanine, Cytosine, Thymine Double helix

Adenine, Guanine, Cytosine, Uracil Single strand, straight or folded/globular

Messenger RNA
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mRNA = messenger RNA
copies DNA’s instructions in nucleus and carries them to the ribosomes in the cytoplasm This information is translated into an amino acid sequence to make a protein. Codon: 3 consecutive bases on mRNA

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Transfer RNA
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  

tRNA = transfer RNA
Cloverleaf shape Carries amino acids in cytoplasm to ribosomes for protein assembly - Reusable Enters ribosome & reads mRNA codon and links together correct sequence of amino acids
 Anticodon: 3 consecutive bases on tRNA (example: mRNA codon (CAG) attaches to tRNA anticodon (GUC)

Transfer RNA

Ribosomal RNA
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 

rRNA = ribosomal RNA
rRNA and protein make up the ribosomes globular shape aids in moving ribosomes along the mRNA strand to “read” the codons

3 types of RNA

Amino Acids
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

20 main amino acids
8 are called essential – since your body cannot synthesize these 8, you must eat them in your diet Amino acids are the monomers of proteins DNA contains the instructions for an amino acid in a 3 base sequence called a triplet. This information is carried to the ribosomes on a mRNA codon.

 

Protein Synthesis
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

Consists of 2 parts
transcription: in nucleus, mRNA copies DNA’s instructions and carries them to the ribosomes (DNA to mRNA) translation: in cytoplasm, tRNA enters ribosomes to read mRNA codons and link together amino acids (mRNA to tRNA to amino acid)



Transcription
 Things to understand that are NOT in your notes: You might want to add this to your notes!!  mRNA synthesis is “rewriting” the info from DNA into mRNA  DNA stays in the nucleus for protection (hard drive) while info is carried to ribosome by mRNA (CD/disc copy)

mRNA Synthesis

Process of Transcription
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 

DNA helicase (enzymes) uncoil and unzip the DNA molecule The 2 DNA strands separate, but ONLY ONE will serve as the template & be copied RNA polymerase (enzyme) binds to a region of DNA called the promoter and joins free nucleotides to form the mRNA strand

Process of Transcription
 mRNA sequence is built until the enzyme reaches an area on DNA called the termination signal or stop codon

Modifications
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 

Eukaryotic mRNA is modified BEFORE leaving the nucleus through nuclear pores, (prokaryotic RNA isn’t)
Sections that do not code for proteins are called introns & are snipped out of the mRNA Sections called exons that code for proteins are spliced together See figure 12-15 page 302



Introns & Exons

Process of Translation
 Things to understand that are NOT in your notes: You might want to add this to your notes!!  Amino acids don’t speak the same language as mRNA so tRNA needs to “translate” the mRNA instructions so the amino acids line up in the correct sequence

Process of Translation
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 

mRNA brings the copied DNA code from the nucleus to the cytoplasm mRNA attaches to one end of a ribosome tRNA’s attach the correct amino acid floating in the cytoplasm & bring them into the correct order

Process of Translation
 Two amino acids at a time are linked together by peptide bonds to make a protein

Process of Translation
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Ribosomes) move along the mRNA strand until they reach a stop codon tRNA’s break loose from amino acid, leave the ribosome, & return to cytoplasm to pick up another amino acid until the protein is complete

Translation Diagram

DNA  Genes  Proteins  Trait

Hyperlinks
 Protein Synthesis

MUTATIONS
CHANGES IN THE GENETIC INFORMATION

Mutations
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Changes in genetic material
Mutations may be neutral, harmful, lethal, or beneficial Gene mutation – produces change in a single gene which codes for a single protein There are also chromosomal mutations that we will discuss later

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Gene mutations
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Changes in one or a few nucleotides are known as point mutations.
substitutions – usually affect only one amino acid insertions or deletions are known as frameshift mutations – may change every amino acid after the point of mutation (much more serious) see fig 12-20 page 307



Sickle Cell Anemia
 Point mutation = One small change = lifelong disorder

Frameshift Mutation


				
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