Unit 4: DNA Replication, Transcription, Translation, and Protein synthesis.

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Laura Mozingo BIO 135 At JCCC

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58 Terms

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Hershey and Chase

DNA is the genetic material.

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Chargaff's Rule

DNA has equal amounts of A=T and G=C.

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Chemical Structure of DNA

(-) including a nitrogenous base, pentose sugar, and phosphate group.

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<p>DNA REPLCIATION</p>

DNA REPLCIATION

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Semiconservative Model of Replication

Type of DNA replication where double helix has parent and daughter strands.

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Leading Strand Replication

Nucleotides continuously added in 5' to 3' direction

TOWARDS replication fork.

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Lagging Strand Replication

Nucleotides discontinuously added in Okazaki fragments in 5' to 3' direction

AWAY from replication fork.

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DNA Polymerase I

Removes RNA nucleotides of primer and replaces them with DNA.

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DNA Polymerase III

Adds nucleotides to RNA primer or DNA strand

Builds new DNA strands.

Uses parental DNA as a template

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Helicase

Unzips DNA at replication forks

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Ligase ‘gluer’

Glues bonds between Okazaki fragments to form one continuous DNA strand.

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Nuclease

Cuts damaged DNA.

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Primase

Makes RNA primer by adding RNA nucleotides.

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RNA Primer

Short nucleotide chain

Starting point for DNA synthesis.

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Single Strand Binding Protein

Binds DNA strands during replication

Stabilizes and keeps separated.

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Telomerase

Adds DNA to telomeres in eukaryotic germ cells, healing their length after replication.

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Topoisomerase

Breaks and rejoins DNA strands after trauma.

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Telomere

Nucleotide sequences at the end of chromosomes

Act as buffer zones and delay shortening of genes

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Histone

Protein molecules that pack DNA into chromatin in interphase.

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Origins of Replication

Sites where DNA replication occurs

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Prokaryotic Origin of Rep.

ONE circular chromosome

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Eukaryotic Origin of Rep.

INFINITE number of linear chromosomes

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Replication Fork

Y-shaped region

Parental strands unwind, and new strands are created.

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Antiparallel Elongation

Two new strands must run ANTIPARALLEL to parent strands.

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Okazaki fragment

Short strands of DNA that make up lagging strand.

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DNA proofreading and repair

DNA polymerases check each nucleotide against its template as it's added. If incorrect, it's removed and corrected.

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Mismatch repair

Enzymes fix DNA mistakes by removing and replacing incorrectly paired nucleotides.

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Nucleotide excision repair

A repair system where damaged DNA is removed and replaced, using undamaged strand as template.

NUCLASE, DNA POLYMERASE, LIGASE

Damage can pass into replication accidentally.

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Telomere function

Acts as a buffer zone, delays gene shortening/loss

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Telomerase function

Adds DNA to telomeres, helping restore length.

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Histones

Proteins that pack DNA in Interphase chromatin.

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Eukaryotic DNA

  • Nucelus

  • Long

  • Linear

  • Many proteins (histones)

  • No correlation with gene #

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Prokaryotic DNA

  • No Nucleus, uses cytoplasm

  • Short

  • Circular

  • Fewer proteins

  • Correlation with gene #

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How is DNA packaged in the cell? How does this change throughout the cell cycle?

Prophase: Condensin II (Large Loops), Condensin I (Small Loops)

Metaphase: chromosomesare fully condensed, MOST dense

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Euchromatin

  • Less condensed chromatin

  • Available for transcription (gene expression)

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Heterochromatin

  • Very compacted chromatin that stays condensed during Interphase

  • Not used for gene expression

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Central Dogma of Molecular biology

DNA —> RNA —> Protein

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Prokaryotic Transcription/Translation

Cytoplasm

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Eukaryotic Transcription/Translation

  • Nucleus

  • Cytoplasm

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<p>Transcription</p>

Transcription

a cell makes an RNA copy of a piece of DNA

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Codon

3 nucleotides in mRNA that code for a specific amino acid or signal the end of protein synthesis. (Stop Signals)

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Template strand

DNA Strand used as a guide to transcribe complementary RNA strand during transcription.

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Coding Strand

  • Not used as template for transcription

  • Has same nucelutide sequence as transcribed RNA strand, but has T (Thymine) instead of U (Uracil)

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TATA box

  • Found in Eukaryotic promoters

  • Transcription initiation complex

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Transcription Factors

Proteins that bind to DNA, helping RNA polymerase attach to the template strand to initiate transcription.

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Describe Eukaryotic pre-mRNA processing.


- Both exons and introns are transcribed into RNA.

  • Introns: interrupted, removed via splicing.

  • Exons: expressed.

  • 5' cap is added.

  • Poly-A tail is added.

  • Location: Nucleus.

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Alternative RNA splicing

  • Different mRNA versions can be produced from the original transcript

  • Depends on the exon included/excluded pattern.

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Results of alternative RNA splicing

More than one kind of protein

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<p>Translation</p>

Translation

  • Happens in ribosomes in the cytoplasm

  • The ribosome reads the mRNA codons

  • tRNA has an anticodon that matches the mRNA codon.

  • tRNA (transfer RNA) brings specific amino acids to the ribosome.

  • They form a polypeptide chain, which becomes a protein

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Wobble

  • Third base of codon.

  • Can pair with more than one base in tRNA anticodon

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What happens to the polypeptide when released from ribosome?

  • Modifications can happen

  • Adding sugars, lipids, phosphates

  • Join or cut polypeptides

  • Remove amino acids

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Signal proteins

  • Amino acid tags on a polypeptide

  • Tell cell where it should go

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Nonsense mutation

  • Premature stop codon

  • Short protein

  • Often non-functional

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Mutation

  • Change in nucleotides in DNA

  • Affects all new genes

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Silent Mutation

  • Same amino acid

  • ‘Silent’

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Missense Mutation

Different amino acid.

  • Can be a slight or drastic effect on protein.

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Nonsense Mutation

Introduces a premature stop codon

  • Short and often non-functional protein.

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What is the difference between substitution, insertion, and deletion? What results in each case?

Substitution: One nucleotide is replaced by another. Can result in silent, missense, or nonsense mutations.


Insertion: Addition of one or more nucleotides. Can cause frameshift mutations, altering the entire protein sequence after the insertion point.


Deletion: Removal of one or more nucleotides. Similar to insertions, can cause frameshift mutations.