Zusammenfassung der Ressource
Gene Expression & Regulation
- DNA, RNA, & Gene Expression
- Converting the information encoded by a gene into its product starts with RNA synthesis, during which
enzymes use the gene's DNA sequence as a template to assemble a strand of RNA.
- RNA usually occurs in a single-stranded form that is similar to a single strand of DNA
- the fourth base in RNA is uracil (U), not thymine as it is in DNA
- DNA's only role is to store genetic information
- rRNA assembles amino acids into polypeptide chains
- tRNA delivers amino acids to ribosomes
- mRNA functions as the "messenger" between DNA and protiens
- Transcription and translation are part of the process called gene expression
- Transcription: DNA to RNA
- The same base-pairing rules also govern RNA synthesis in transcription
- DNA as a Template
- DNA replication begins with one DNA double helix and ends with two DNA double helices
- An RNA strand is structurally so similar to a DNA strand that the two can base-pair if their nucleotide
sequences are complementary (U pairs up with A)
- A strand of DNA acts as a template upon which a strand of RNA is assembled from
- Only part of one DNA strand (not the whole molecule) serves as the template
- Produces a single strand of RNA, and DNA replication produces two DNA double helices
- Process of Transcription
- In eukaryotic cells, transcription occurs in the nucleus; in prokaryotes, it occurs in cytoplasm
- The polymerase starts moving along the DNA, over the gene region
- The polymerase unwinds and joins free RNA nucleotides in the order dictated by that DNA sequence
- DNA and RNA are released. RNA polymerase follows base-pairing rules, so the new RNA strand is
complementary to the DNA strand from which it was transcribed
- RNA Modification
- Introns are removed in chunks from a newly transcribed RNA before it
leaves the nucleus
- A tail of 50 to 300 adenines is added to the end of a new
mRNA (poly-A tail)
- mRNA carries DNA's protein-building information which consist of codons
- All codons make the genetic code
- Each tRNA has an anticodon that can base-pair with a codon, and it binds to the amino acid specified by that
codon
- Enzymatic rRNA and proteins make up the two subunits of ribosomes
- RNA Players in Translation
- In eukaryotic cells, RNA is transcribed in the nucleus
- Finished RNA moves into the cytoplasm through nuclear pores
- Ribosomal subunits and tRNA converge on an mRNA
- A polypeptide chain forms as the ribosome moves
along the mRNA, linking amino acids together in the
order dictated by the mRNA codons
- The ribosome then begins to assemble a polypeptide chain as it moves along the mRNA
- The first tRNA is released and the ribosome moves to the next codon
- The second tRNA is released and the ribosome moves to the next codon
- The new polypeptide chain continues to elongate
- Translating the Code: RNA to Protein
- Mutated Genes & Their Protein Products
- Eukaryotic Gene Controls