Central DogmaCentral DogmaDNA DNA RNA RNA

ProteinProtein

……..Which leads ..Which leads to to TraitsTraits

How Does DNA produce How Does DNA produce traits?traits?

1. Genes control proteins which 1. Genes control proteins which determine traitsdetermine traits

2. Order of nucleotides in the DNA 2. Order of nucleotides in the DNA determines amino acid sequencedetermines amino acid sequence

RNA's act as 'go-between' for DNARNA's act as 'go-between' for DNA Gene- a sequence of DNA with a Gene- a sequence of DNA with a

specific functionspecific function

RNARNA Single strand of nucleotides (unlike DNA)Single strand of nucleotides (unlike DNA) Contains 5-C sugar riboseContains 5-C sugar ribose Uracil replaces ThymineUracil replaces Thymine 3 types of RNA produced3 types of RNA produced

1. 1. Messenger RNA (m-RNA)Messenger RNA (m-RNA) - code for order of - code for order of amino acids amino acids

2. 2. Transfer RNA (t-RNA)Transfer RNA (t-RNA) - carry amino acids and fit - carry amino acids and fit them in them in proper placeproper place

3. 3. Ribosomal RNA (r-RNA)Ribosomal RNA (r-RNA) - major component of - major component of ribosome; ribosome; large and small subunitslarge and small subunits

a. P site: carries the growing polypeptide a. P site: carries the growing polypeptide chainchain

b. A site: delivers the next amino acid to the b. A site: delivers the next amino acid to the growing growing chainchain

CodonsCodons

CodonsCodons – 3 nucleotide sequences – 3 nucleotide sequences coded from the original DNA strand coded from the original DNA strand onto a mRNA strand.onto a mRNA strand.

Each codon corresponds to an amino Each codon corresponds to an amino acid or a stop/start signalacid or a stop/start signal

The codon on a mRNA strand is The codon on a mRNA strand is complementary to an anti-codon on complementary to an anti-codon on tRNAtRNA

Codons in mRNA

Going from DNAGoing from DNARNARNA

Transcription - Formation of m-Transcription - Formation of m-RNA molecule from a DNA RNA molecule from a DNA template – occurs in the nucleus.template – occurs in the nucleus.

Occurs in three steps: Occurs in three steps:

1.1. InitiationInitiation

2.2. ElongationElongation

3.3. TerminationTermination

InitiationInitiation

RNA polymerases bind to DNA at RNA polymerases bind to DNA at regions called promoters (initiation regions called promoters (initiation site, also called TATA box); the site, also called TATA box); the enzyme then separates the 2 DNA enzyme then separates the 2 DNA strands and transcription begins.strands and transcription begins.

RNA polymerase reads DNA from 3’ RNA polymerase reads DNA from 3’ to 5’to 5’

ElongationElongation

• • RNA polymerases move along the RNA polymerases move along the DNA and:DNA and:

-untwists and opens a short segment -untwists and opens a short segment of DNA (DNA template)of DNA (DNA template)

- links incoming RNA nucleotides to - links incoming RNA nucleotides to the 3' end of the elongating strand; the 3' end of the elongating strand; RNA grows one nucleotide at a time RNA grows one nucleotide at a time in the 5' to 3' directionin the 5' to 3' direction

TerminationTermination

Transcription proceeds until RNA Transcription proceeds until RNA polymerases reaches a termination polymerases reaches a termination site on the DNA; RNA molecule is site on the DNA; RNA molecule is then released and leaves the then released and leaves the nucleus.nucleus.

The DNA strand then joins back The DNA strand then joins back together – unchanged.together – unchanged.

TranslationTranslation

Translation – using the mRNA strand Translation – using the mRNA strand made during Transcription and tRNA made during Transcription and tRNA and rRNA to build a protein.and rRNA to build a protein.

Occurs at the site of protein Occurs at the site of protein synthesis – the ribosome.synthesis – the ribosome.

Occurs in three steps – the same but Occurs in three steps – the same but different than transcription – different than transcription – initiation, elongation, and initiation, elongation, and termination.termination.

InitiationInitiation

1. the small ribosomal subunit 1. the small ribosomal subunit attaches to the 5' end of the attaches to the 5' end of the mRNA ('start' codon -AUG)mRNA ('start' codon -AUG)

2. a tRNA (with anticodon 2. a tRNA (with anticodon UAC) carries the amino acid UAC) carries the amino acid methionine to the mRNA methionine to the mRNA

ElongationElongation

1. the next tRNA binds to the ribosome; 1. the next tRNA binds to the ribosome; the new amino acid is attached to first the new amino acid is attached to first oneone

2. the first tRNA is released and binds 2. the first tRNA is released and binds again with other amino acids (repeated again with other amino acids (repeated deliveries)deliveries)

3. a new tRNA attaches to the ribosome 3. a new tRNA attaches to the ribosome and repeats the process, thereby and repeats the process, thereby increasing the polypeptide chain lengthincreasing the polypeptide chain length

TerminationTermination

1.1. Occurs when the Occurs when the ribosome encounters a ribosome encounters a 'stop' codon.'stop' codon.

2.2. The resulting protein The resulting protein formed is now released formed is now released and is used by the cell.and is used by the cell.