concept 13 - BIO10008

what is the enzyme that synthesises RNA

RNA polymerase

how does this enzyme recognise transcriptional start sites

recognises promotors to initiate transcription

how does this RNA polymerase recognise transcriptional start sites in eukaryotes

using general promotors to initiate transcription and transcriptional factors

how does this RNA polymerase recognise transcriptional start sites in prokaryotes

also using promotors but sigma factors aid this process without other proteins to help

initiation in prokaryotes and eukaryotes

the promotor on the DNA is bind to the RNA polymerase which then will start unwinding the double stranded DNA - forming the template and the complementary strand

elongation in prokaryotes and eukaryotes

the unwinding is continued where the RNA polymerase travels from a 5’ to 3’ direction, but DNA complementary pairs are introduced into the template strand where T→U. whilst RNA is exiting the transcript.

what is the central dogma

the sequential flow of genes is from dna → rna → proteins for gene expression

termination in eukaryotes and prokaryotes

there will be a termination sequence where the RNA will split off and is read in a 5’ to 3’ direction, and the DNA is regenerated. This generated RNA will have the same 5’ to 3’ direction as the complementary strand of the DNA. (except it has uracil)

what strand of the DNA has the same sequence (except U in place of T) as the transcribed RNA molecule

the complementary strand has the same sequence as the transcribed RNA (5’ → 3’)

what is the other strand (not complementary) called and what is its purpose

the other strand is the template strand it serves as a template for the transcribed RNA and is read in 3’→5’. this is antiparallel to ensure if there is damage in the DNA that repairs are fast.

how, where and why eurkaryotic mRNA are processed

mRNA is processed in the nucleus by RNA pol. 2, and is needed to be processed to transport the information in the ribosome for translation. This is through the spliting of introns, leaving coding exons and the addition of 5’ caps and 3’ poly-a tails.

how, where and why prokaryotic mRNA are processed

through RNA polymerase 2, in the cytoplasm coupled with transcription and translation as prokaryotes lack a nucleus.

define features of an open reading frame

starts with a start codon and ends with a stop codon and is read in triplets

describe the effects of translation in the incorrect reading frame

incorrect reading frame could lead to wrong translations of protein thus amino acids are misread and the function of the protein is altered

describe what is meant by the degeneracy of the genetic code

sometimes if there is a single point mutation in the genetic code, it can still be read as the same amino acid as some amino acids have multiple codes that translates to the same amino acid

what is a possible advantage of degeneracy of the genetic code

if there is a mutation that is substituting a letter in the triplet code, if that letter can also be translated into the same amino acid, the protein will still retain its functions. thus this is a silent synonmous mutation

what are the three main RNA produced

tRNA - helps translate the mRNA into proteins

rRNA - ribosomal DNA

mRNA - messenger RNA helps with transporting the RNA transcripted from nucleus to cytoplasmthrough splitting of introns and additions of exon and adding 5’ caps and 3’ poly-a tails.

tRNA structure

has an anticodon on the bottom that is complementary to the mRNA codon, recognises the correct amino acid to deliver

has an amino acid attachment site (ALWAYS CCA) to the 3’ end of the now CHARGED tRNA when amino acid is attached → delivers amino acid during translation

what is translation

translation is the process of translating mRNA into amino acids/protein with the help of tRNA in the ribosome

describe the difference between translation initiation in prokaryotes and eukaryotes

prokaryotes have a shin delgado sequence for the small subunit of ribosomes to recognise, eukaryotes do not have and the initiation starts by the binding of the small subunit of ribosome onto the mRNA through recognition of the 5’ cap then is scanned for a start codon.

how do tRNAs help ribosome introduce the correct amino acid to a polypeptide

tRNA has a section at the bottom with an anticodon loop complementary to the mRNA sequence, where the amino acid will then be attached from their attachment site (CCA) when it is charged

initiation of translation

prokaryotes - the small subunit ribosome will recognise the start codon when binded to a shin delgado sequence.

eukaryotes - the small subunit ribosome will recognise the 5’ cap put onto the mRNA after transcription

then a tRNA charged with MET (on the CCA attachment site) comes in with an anticodon complementary to the start codon so it binds to it. then a large subunit of ribosome comes, the tRNA is in the P site.

elongation in translation

the ribosome moves in a 5’ to 3’ direction, as another tRNA charged with another amino acid with an anticodon complementary to the next part of the mRNA enters the A site, the amino acids form a peptide bond catalysed by the ribosome. Then the uncharged tRNA (the start codon one) will be released through the E site. This process is repeated until reaching a stop codon.

termination in translation

there is no tRNA (anticodon that is complementary to the stop codon) recognising the stop codon, thus a release factor comes in the A site and separates the polypeptide and tRNA. Thus, leading to mRNA and ribosome separating…

describe how gene expression can allow an organism to have specialised cell types with different functions any steps/processes that may influence gene expression in cells.