GENE EXPRESSION Gene Expression Our phenotype is the

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GENE EXPRESSION

GENE EXPRESSION

Gene Expression Our phenotype is the result of the expression of proteins Different alleles

Gene Expression Our phenotype is the result of the expression of proteins Different alleles encode for slightly different proteins Protein variation is the basis for normal phenotypic variation - blue or brown eyes It is also the basis for abnormal phenotypes - cystic fibrosis

In the late 1930 s, early 40 s, Beadle and Tatum - working with

In the late 1930 s, early 40 s, Beadle and Tatum - working with a mold – Neurospora - observed that a mutation in a single gene caused the loss of a single enzyme, and that this resulted in a mutant phenotype This established that genes produce phenotypes through the action of proteins Awarded the Nobel Prize in Medicine in 1958

Central Dogma Replication DNA Transcription RNA Translation Nucleus Protein Cytoplasm

Central Dogma Replication DNA Transcription RNA Translation Nucleus Protein Cytoplasm

Gene Expression Together transcription and translation are called gene expression. The genetic information encoded

Gene Expression Together transcription and translation are called gene expression. The genetic information encoded in the DNA of an embryo includes all of the genes needed to develop and maintain the organism. Different cell types express different subsets of genes.

Transcription DNA is used as a template for creation of RNA using the enzyme

Transcription DNA is used as a template for creation of RNA using the enzyme RNA polymerase. DNA 5 ’ 3’ GT CA TT CGG 3’ C AG T AAGCC 5’

Transcription RNA polymerase reads the nucleotides on the template strand from 3’ to 5’

Transcription RNA polymerase reads the nucleotides on the template strand from 3’ to 5’ and creates an RNA molecule that looks like the coding strand. DNA coding strand 5 ’ 3’ DNA GT CA TT CGG 3’ C AG T AAGCC DNA template strand 5’

Transcription The new RNA molecule is formed by incorporating nucleotides that are complementary to

Transcription The new RNA molecule is formed by incorporating nucleotides that are complementary to the template strand. DNA coding strand 5 ’ 3’ DNA GT CA TT CGG 3’ G UC AUUCG G 3’ C AG T AAGCC 5’ DNA template strand RNA 5 ’

Two types of nucleic acids RNA DNA Usually single-stranded Usually double-stranded Has uracil as

Two types of nucleic acids RNA DNA Usually single-stranded Usually double-stranded Has uracil as a base Has thymine as a base Ribose as the sugar Deoxyribose as the sugar Carries protein-encoding information Carries RNA-encoding information Can be catalytic Not catalytic

# of strands kind of sugar bases used

# of strands kind of sugar bases used

Types of RNA Abbrev. Function m. RNA Messenger RNA - encodes protein r. RNA

Types of RNA Abbrev. Function m. RNA Messenger RNA - encodes protein r. RNA Ribosomal RNA - part of ribosome - used to translate m. RNA into protein t. RNA Transfer RNA - couples the region which binds the m. RNAcodon and its amino acid

r. RNA is part of ribosome, used to translate m. RNA into protein

r. RNA is part of ribosome, used to translate m. RNA into protein

t. RNA is a connection between anticodon and amino acid

t. RNA is a connection between anticodon and amino acid

Transcription Occurs in three steps: Initiation Elongation Termination

Transcription Occurs in three steps: Initiation Elongation Termination

RNA processing m. RNA transcripts are modified before use as a template for translation:

RNA processing m. RNA transcripts are modified before use as a template for translation: - Addition of capping nucleotide at the 5’ end - Addition of poly. A tail to 3’ end Þ Þ Important for moving transcript out of nucleus And for regulating when translation occurs Splicing - the removing internal sequences - introns are sequences removed - exons are sequences remaining

RNA processing

RNA processing

Translation • The process of reading the RNA sequence of an m. RNA and

Translation • The process of reading the RNA sequence of an m. RNA and creating the amino acid sequence of a protein is called translation. DNA Transcription T T C A G A A G U C DNA template strand Messenger RNA m. RNA Codon Translation Protein Lysine Serine Valine Polypeptide (amino acid sequence)

The genetic code There is a 3 to 1 correspondence between RNA nucleotides and

The genetic code There is a 3 to 1 correspondence between RNA nucleotides and amino acids. The three nucleotides used to encode one amino acid is called a codon. The genetic code refers to the codons that encode each amino acids.

What is the correspondence between the m. RNA nucleotides and the amino acids of

What is the correspondence between the m. RNA nucleotides and the amino acids of the protein? Proteins are formed from 20 amino acids in humans. Codons of one nucleotide: A G C U Can only encode 4 amino acids Codons of two nucleotides: AA GA CA UA AG GG CG UG AC GC CC UC AU GU CU UU Can only encode 16 amino acids

Codons of three nucleotides: AAA AGA ACA AUA AAG AGG ACG AUG AAC AGC

Codons of three nucleotides: AAA AGA ACA AUA AAG AGG ACG AUG AAC AGC ACC AUC AAU AGU ACU AUU GAA GGA GCA GUA GAG GGG GCG GUG GAC GGC GCC GUC GAU GGU GCU GUU CAA CGA CCA CUA CAG CGG CCG CUG CAC CGC CCC CUC CAU CGU CCU CUU UAA UGA UCA UUA UAG UGG UCG UUG UAC UGC UCC UUC UAU UGU UCU UUU Allows for 64 potential codons => sufficient!

A codon of three nucleotides determines choice of amino acid

A codon of three nucleotides determines choice of amino acid

The genetic code is non-overlapping

The genetic code is non-overlapping

The genetic code is universal - All known organisms use the same genetic code.

The genetic code is universal - All known organisms use the same genetic code. (Rare organisms use one codon for an additional amino acid. ) The genetic code is degenerate Some codons encode the same amino acid. e. g. GGU, GGC, GGA, and GGG all encode glycine Degeneracy is mostly at the third base of the codon. Some codons have additional functions AUG encodes methionine. Methionine can be used within a protein sequence and is often the first amino acid cueing the beginning of translation. UAA, UAG, and UGA do not encode an amino acid. These codons signal termination of the protein.