BIOLOGY 201L Chapter Notes - Chapter 7: Tata Box, Gene Expression, Ribosome
Chapter 7 - From DNA to Protein: How Cells Read the
Genome
Saturday, February 20, 2016
5:16 PM
Genes can be transcribed and RNA can be translated at different rates, giving cell a way to make big
quantities of some proteins and tiny quantities of others.
In prokaryotes, as RNA is being made, the RNA is also being translated. Pro-transcription-translation
In eukaryotes transcription is sequestered
Transcription - copy nucleotide sequence of DNA into RNA
• Begins by opening and unwinding small portion of DNA to expose bases on each DNA strand. One
strand acts as template for RNA synthesis
• Ribonucleotides are added and covalently linked to each other by RNA polymerase. Moves
downstream. Only alpha phosphate is incorporated into strand.
RNA polymerase use ribonucleosides, not deoxyribonucleosides, and they don't need a
primer. Needs DNA template, ribonucleotides, and divalent metal ion (Mg or Mn)
o One mistake every 10^4 nucleotides
o Eukaryotes have 3 polymerases: RNA polymerase I, II, and III. I and III transcribe genes for
tRNA, rRNA, and RNAs with structural and catalytic roles in cell. II does most genes,
including those that encode proteins and miRNAs.
o For eukaryotes, general transcription factors have to assemble at each promoter so
polymerase can start transcription. They are accessory proteins that pull apart DNA to
expose template strand. Bind to TATA box on DNA
• RNA transcript is RNA chain produced by transcription; has sequence complementary to template
DNA
• RNA chain extended in 5' to 3' direction
• Non-template strand is coding strand.
Synthesis of next RNA is usually started before the first RNA is completed, so transcription is really quick.
Since RNA is single stranded, it can fold into a variety of shapes, so can do various functions in cells.
Messenger RNAs (mRNAs) carry info about protein amino acid sequences. Each one carries info
transcribed from one gene for single protein.
• Bacteria mRNA could carry info for multiple proteins
Ribosomal RNAs (rRNAs) form structural and catalytic core of ribosomes
Transfer RNAs act as adaptors that select specific amino acids and hold them in place on a ribosome
MicroRNAs (miRNAs) are key regulators of eukaryotic gene expression
Other noncoding RNAs are used in RNA splicing, gene regulation, telomere maintenance, etc. Most RNA
is NONCODING.
Gene expression is process by which the info encoded in DNA sequence is translated into a product that
affects cell or organism.
Transcription initiation is the main point at which the cell selects which proteins or RNAs are to be
produced.
Promoter is gene region with specific sequence of nucleotides that lies upstream of starting point for
synthesis
• Every promoter has certain polarity that helps promoter bind to certain strand. It uses 3'-5' DNA
strand as template cuz polymerase goes 5'-3'
Promoters determine:
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Chapter 7 - from dna to protein: how cells read the. Genes can be transcribed and rna can be translated at different rates, giving cell a way to make big quantities of some proteins and tiny quantities of others. In prokaryotes, as rna is being made, the rna is also being translated. Transcription - copy nucleotide sequence of dna into rna: begins by opening and unwinding small portion of dna to expose bases on each dna strand. One strand acts as template for rna synthesis: ribonucleotides are added and covalently linked to each other by rna polymerase. Rna polymerase use ribonucleosides, not deoxyribonucleosides, and they don"t need a primer. Needs dna template, ribonucleotides, and divalent metal ion (mg or mn: one mistake every 10^4 nucleotides, eukaryotes have 3 polymerases: rna polymerase i, ii, and iii. I and iii transcribe genes for trna, rrna, and rnas with structural and catalytic roles in cell.
