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PROTEIN PROTEIN SYNTHESISSYNTHESIS

PreviewPreview

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Protein SynthesisProtein Synthesis The production (synthesis) of The production (synthesis) of

polypeptide chains polypeptide chains (proteins)(proteins) Two phases:Two phases:

Transcription Transcription & & TranslationTranslation mRNA must be mRNA must be processed before processed before

it leaves the nucleusit leaves the nucleus of of eukaryotic cellseukaryotic cells

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TranscriptionTranscription

TranslationTranslation

DNA

mRNA

Ribosome

Protein

Prokaryotic CellProkaryotic Cell

DNA DNA RNA RNA ProteinProtein

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DNA DNA RNA RNA ProteinProtein

Nuclearmembrane

TranscriptionTranscription

RNA ProcessingRNA Processing

TranslationTranslation

DNA

Pre-mRNA

mRNA

Ribosome

Protein

EukaryotEukaryotic Cellic Cell

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Pathway to Making a Pathway to Making a ProteinProtein

DNADNA

mRNAmRNA

tRNA (ribosomes)tRNA (ribosomes)

ProteinProtein

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Nucleic Nucleic AcidsAcids

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DNA or Protein?DNA or Protein? 1903, Walter Sutton noted the parallelism

between chromosome behavior and Mendel's laws, thus identifying genes with chromosomes and marking the beginning of genetics as a science

However, scientists were However, scientists were NOTNOT sure which one sure which one (protein or DNA) was (protein or DNA) was the the actual genetic material of actual genetic material of the cellthe cell

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DNA!DNA! Frederick GriffithFrederick Griffith in 1928 in 1928

discovered what he called a transforming principle, which led to the direct discovery of how DNA works and the beginning of

Molecular Genetics.

It wasn't until 1944 that Griffith's "transforming principle" was identified as DNA by Oswald Theodore Avery, along with coworkers Colin MacLeod and Maclyn McCarty

DNA!DNA!• Rosalind Franklin recorded a x-ray

photograph of a DNA molecule that another researcher at King's College, Maurice Wilkins, showed to James Watson and Francis Crick without her knowledge or permission. This image helped Watson and Crick construct a model of DNA, which enabled them to fully understand the molecule's structure.

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• Watson and Crick constructed a model of DNA, which enabled them to fully understand the molecule's structure. Wilkins, Crick and Watson were awarded a Nobel Prize jointly, some years later, after Franklin's death.

• proposed the double helix or spiral staircase structure of the DNA molecule in 1953

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DNA!DNA!

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Watson

Crick

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Structure of DNAStructure of DNA DNA is made of subunits called DNA is made of subunits called

nucleotidesnucleotides DNA nucleotides are composed DNA nucleotides are composed

of a:of a:1.1. phosphatephosphate, ,

2.2. deoxyribose deoxyribose sugar, and sugar, and

3.3. nitrogen-containing basenitrogen-containing base The 4 bases in DNA are: The 4 bases in DNA are: adenine adenine

(A), (A), thymine (T),thymine (T), guanine (G),guanine (G), and cytosine (C)and cytosine (C)

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DNA NucleotideDNA Nucleotide

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Base Pairing RuleBase Pairing Rule• Watson and Crick showed that DNA Watson and Crick showed that DNA

is a is a double helixdouble helix• AA (adenine) pairs with (adenine) pairs with TT (thymine) (thymine)• CC (cytosine) pairs with (cytosine) pairs with GG (guanine) (guanine)

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Nitrogen RingsNitrogen Rings• PurinesPurines have have double double rings of rings of

carbon-nitrogen (G, A)carbon-nitrogen (G, A)

Nitrogen RingsNitrogen Rings

• PyrimidinesPyrimidines have have single single carbon-nitrogen rings (C, T)carbon-nitrogen rings (C, T)

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Nitrogen RingsNitrogen Rings

• This is called This is called complementarcomplementary base pairingy base pairing because a because a purinepurine is is always paired always paired with a with a pyrimidinepyrimidine

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.5’ to 3’ Sugars5’ to 3’ Sugars

When the DNA When the DNA double helixdouble helix unwinds, it unwinds, it resembles a ladderresembles a ladder The The sidessides of the ladder are the of the ladder are the sugar-phosphate backbonessugar-phosphate backbones The The rungsrungs of the ladder are of the ladder are the the complementary paired complementary paired basesbasesThe two DNA strands are The two DNA strands are anti-anti-parallel parallel (they run in opposite (they run in opposite directions)directions)

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Anti-Parallel Strands of DNA

Template (top part of DNA)

always goes

from 5’ to 3’

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DNA DNA ReplicatiReplicati

onon

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Steps in DNA Steps in DNA ReplicationReplication

Occurs when Occurs when chromosomes duplicatechromosomes duplicate (make copies) – Interphase (S-phase)(make copies) – Interphase (S-phase) An An exact copyexact copy of the DNA is produced of the DNA is produced with the aid of the enzyme with the aid of the enzyme DNA DNA polymerasepolymerase Hydrogen bondsHydrogen bonds between bases between bases breakbreak and enzymes called and enzymes called helicaseshelicases “unzip” “unzip” the moleculethe molecule Each Each old strandold strand of nucleotides serves of nucleotides serves as a as a templatetemplate for each new strand for each new strand New nucleotidesNew nucleotides move into move into complementary positions are joined by complementary positions are joined by DNA polymeraseDNA polymerase

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Two New, Two New, Identical Identical

DNA DNA Strands Strands Result Result from from

ReplicatiReplicati

onon

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Another View of Another View of ReplicationReplication