From Gene to Protein

Chapter 17

Warm Up Exercise

• What is a telomere?• Explain how DNA is packed tightly into a

chromosome.

Gene Expression

• Gene Expression- DNA inherited by an organism leads to specific traits by dictating the synthesis of proteins. (Proteins therefore are the link between genotype and phenotype).– Gene expression occurs in two steps- transcription

and translation.

Transcription and Translation

• Transcription- the synthesis of RNA using information in the DNA.– Occurs in the nucleus.

• Translation- the synthesis of a polypeptide from mRNA.– Occurs on the ribosome

Transcription and Translation

• Primary Transcript- the initial RNA from any gene. Includes RNA that is not translated into protein.

Transcription and Translation

• Template Strand- the single DNA strand from which the mRNA is transcribed.

Transcription and Translation

• Codons- a series of 3 bases on the mRNA, read together to code for a specific amino acid.

Codon Charts

Warm Up Exercise

• What is a codon?• What is meant by the term primary transcript?

Trascription

• RNA Polymerase- pries two strands of DNA apart and joins RNA nucleotides that are complementary to the DNA template strand.– RNA Pol II specifically is used for mRNA synthesis.

• Promoter- specific DNA sequence where RNA polymerase attaches and begins transcription.– Start Point- the nucleotide where RNA synthesis

actually begins. Found on the promoter gene.

• Transcription Unit- the stretch of DNA that is transcribed into RNA.

Stages of Transcription

• Initiation– Transcription Factors-

mediate the binding of RNA polymerase and initiate transcription (in eukaryotes).

– Transcription Initiation Complex- Transcription Factors + RNA Pol II + Promoters

– TATA Box- promoter DNA sequence

Stages of Transcription

• Elongation– RNA Polymerase

moves along the DNA, unwinding the double helix for pairing with RNA nucleotides.

Stages of Transcription

• Termination– Terminator sequence in bacteria causes RNA

polymerase to detach from DNA.

– In eukaryotes, RNA pol II transcribes a polyadenylation signal. Proteins then cut the transcribed RNA free from polymerase, releasing the pre-mRNA (aka: primary transcript).

Modifying RNA After Transcription

• RNA Processing- modification of pre-mRNA before it is released from the nucleus.– 5’ Cap- a modified guanine (G) nucleotide added on

the 5’ end after transcription.

– Poly-A Tail- a series of 50-250 adenine (A) nucleotides added at the 3’ end of the pre-mRNA.

Modifying RNA After Transcription

• RNA Splicing- removal of large portions of the RNA molecule that is initially synthesized.– Introns- noncoding sequences in the DNA/RNA.

(Intervening sequences)

– Exons- coding sequences in the DNA/RNA. (Expressed sequences)

Modifying RNA After Transcription

• snRNPs (“snurps”)- a short nucleotide sequence at the end of an intron that recognizes splice sites.

• Spliceosome- several snRNPs joined together with proteins. Interacts with sites along the intron, releasing the intron which is rapidly degraded- and joining the exons.

Modifying RNA After Transcription

• Ribozymes- RNA molecules that function as enzymes.

• Domains- a discrete structural and functional region of a protein- coded for by a specific exon.

Warm Up Exercise

• Explain the difference between introns and exons?

• What is a snurp? A spliceosome?

Translation

• Transfer RNA (tRNA)- transfers amino acids from the cytoplasm to the growing polypeptide on a ribosome.– tRNA molecule has a

specific amino acid at one end, and a nucleotide triplet, called an anticodon at the other end, which pairs with a complementary codon on the mRNA.

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