Chapter 17: Gene Expression
Explain the significance of transcription factor
- Molecules (usually proteins) that regulate gene expression by binding to DNA & initiating transcription - Transcription factors are required for RNA pol II binding to promoter. TFs are DNA binding proteins, but can also bind other TFs. They assist in bringing RNA pol II in close proximity of the promoter.
Discuss the role of prompters in eukaryotic transcription
- is a DNA segment - allows a gene to be transcribed - helps RNA polymerase find where the gene starts
List the different steps in eukaryotic transcription
1) initiation 2) elongation 3) chemical modification 4) termination 5) polyadenylation 6) intron splicing
Describe the different steps in protein synthesis
1. DNA unzips between its pairs, then one of the strands of DNA directs the production of mRNA. 2. A ribosome attaches to mRNA in the cytoplasm, specific amino acids are attached to the tRNA. 3. Molecules of tRNA and amino acids attach to mRNA. 4. Transfer molecules attach one at a time to the ribosome and continue to read the message 5. The protein continues to grow until the ribosome reaches a three-base code that signals it to stop.
Discuss the different types of mutations in DNA and its effect in protein synthesis
1. Missense mutation: - changes an amino acid to another amino acid. This may or may not affect protein function, depending on whether the change is "conservative" or "nonconservative," and what the amino acid actually does. 2. Nonsense mutation: - changes an amino acid to a STOP codon, resulting in premature termination of translation. 3. "Silent" mutation: - does not change an amino acid, but in some cases can still have a phenotypic effect, e.g., by speeding up or slowing down protein synthesis, or by affecting splicing. 4. Frameshift mutation: - Deletion or insertion of a number of bases that is not a multiple of 3. Usually introduces premature STOP codons in addition to lots of amino acid changes.
Describe different types of mutagens
1. Physical Mutagens -Ionizing radiation: cosmic rays, X-rays and gamma rays. - Ultraviolet radiation from sunlight. 2. Chemical Mutagens -Base analogs -Base modifying agent -Intercalating agents
Discuss the role of RNA polymerases in transcription
RNA polymerase binds to DNA, separates the strands, then uses one of the strands as a template from which to assemble nucleotides into a complementary RNA strand
Discuss the role of ribosomes in protein synthesis
Ribosomes use the sequence of codons in mRNA to assemble amino acids into polypeptide chains
Understand the significance of exons, introns, and splicing for mRNAs
exon: coding sequences intron: noncoding intervening sequences found in RNA splicing for mRNAs: a process that removes introns from pre-mRNA and converts pre-mRNA into mRNA and occurs with great precision to avoid the loss or addition of nucleotides at the sites where exons are joined
Explain the role of tRNAs and rRNAs in protein synthesis
transfer RNA (tRNA) - delivers the amino acids to the ribosomes so that they can be assembled into a polypeptide chain. Has anticodons. T is replaced with U Ribosomal RNA ( rRNA) - makes the ribosomes themselves and helps to "read" the information from mRNA
Understand genetic code, codon, triplets
Genetic code - Genetic code is the set of instructions, in the form of nucleotide triplets, that translate a linear sequence of nucleotides in mRNA into a linear sequence of amino acids in a protein. Codon - Codon are three nucleotides in messenger RNA (mRNA) that direct the placement of a particular amino acid into a polypeptide chain Triplet - Triplet is a sequence of three nucleotides on a DNA or RNA molecule, which codes a specific amino acid in protein synthesis.
Explain the "central dogma" of DNA-protein synthesis
The central dogma of molecular biology describes the two-step process, transcription and translation, by which the information in genes flows into proteins: DNA → RNA → protein. Transcription is the synthesis of an RNA copy of a segment of DNA.