How genes in DNA can provide instructions for proteins. The central dogma of molecular biology: DNA→ RNA→ protein.
Log in afzal.siddique99 8 years agoPosted 8 years ago. Direct link to afzal.siddique99's post “Why there are 61 codons? ...” Why there are 61 codons? Why not 64?? • (42 votes) Christian Krach 8 years agoPosted 8 years ago. Direct link to Christian Krach's post “3 of them are stop-codons...” 3 of them are stop-codons which terminates translation (61+3=64). (100 votes) SRINIDHI MEDARI 8 years agoPosted 8 years ago. Direct link to SRINIDHI MEDARI's post “what happens to the mRNA...” what happens to the mRNA after translation process i.e after proteins are produced? • (33 votes) Jonathan 3 years agoPosted 3 years ago. Direct link to Jonathan's post “Hi Srinidhi,After mRNA ...” Hi Srinidhi, After mRNA is translated, is either stored for later translation or is degraded. The eventual fate for every mRNA molecule is to be degraded. The process of degrading mRNA molecules happens at a relatively fixed rate. Hope this helps! Jonathan Myung (8 votes) andrewshemon189 7 years agoPosted 7 years ago. Direct link to andrewshemon189's post “I'm still confused on two...” I'm still confused on two things. One, what is a TATA box? ANd two, what are the poly-a tails and 5' caps? • (14 votes) aiwen.joy.lim 7 years agoPosted 7 years ago. Direct link to aiwen.joy.lim's post “The TATA box tells where ...” The TATA box tells where a gene begins so that it can be transcribed. The Poly-A tail is a string of (mostly) adenines on the 3' end of the mRNA that gets eaten away by hydrolytic enzymes. It is there so that the coding section of the mRNA doesn't get eaten. (The hydrolytic enzymes themselves are there to protect from viruses.) It is also recognized by the nuclear pore and allows the mRNA to leave the nucleus. The 5' cap tells the ribosome where to begin translating. (26 votes) Joyrell Thompson 8 years agoPosted 8 years ago. Direct link to Joyrell Thompson's post “What happens if a mRNA br...” What happens if a mRNA breaks? Will part of the protein be produced from the broken piece? • (5 votes) DeepankarRoy 8 years agoPosted 8 years ago. Direct link to DeepankarRoy's post “Yes, most likely. If the ...” Yes, most likely. If the context of the mRNA fits with the translational machinery (applicable for the part of mRNA with the initiation codon only. The part without the initiation codon would not be translated), it might produce a truncated protein where the N-terminal part would be present but the C-terminal part (wrt to the original full length protein) would not be there. However, most of these truncated proteins are recognized by the cellular repair machinery as abnormal and they are recycled. Sometimes though, such proteins can linger and may even participate in cellular functions (in a positive or detrimental way). Most likely source of truncated proteins is DNA rearrangement though, and mRNA breakage would not likely have a major effect (it might, depending upon the need of the original protein) as there would be other full-length mRNAs that would be translated into the protein of interest. Hope this helps. (15 votes) stephen4934 5 years agoPosted 5 years ago. Direct link to stephen4934's post “What is tRNA using to cre...” What is tRNA using to create these amino acids? Do they come from tge nutrition of what you eat? • (4 votes) tyersome 5 years agoPosted 5 years ago. Direct link to tyersome's post “The tRNA doesn't create a...” The tRNA doesn't create amino acids, it acts as an adaptor that recognizes a codon in an mRNA bound to a ribosome. Depending on the amino acid and the organism, those amino acids may have come from food or been synthesized within the cell. In cells, amino acids are activated by being bound to a tRNA - this is done by an enzyme called "aminoacyl tRNA synthetase". You can learn more about tRNAs and how they are charged with amino acids here: And for more detail on aminoacyl tRNA synthetase see: https://en.wikipedia.org/wiki/Aminoacyl_tRNA_synthetase Does that help? (6 votes) Lunalgaleo 4 years agoPosted 4 years ago. Direct link to Lunalgaleo's post “What happens in a mutatio...” What happens in a mutation where the Stop Codon is removed/altered? What does the cell do then? does it perform apoptosis? • (4 votes) Ivana - Science trainee 4 years agoPosted 4 years ago. Direct link to Ivana - Science trainee's post “There are repair mechanis...” There are repair mechanisms. That one is called Non stop Decay that mechanism is able to detect mRNA which cannot be degraded because there is no STOP codon. It has to detach mRNA from the ribosome so it can translate the next mRNA sequence. Nonstop decay is the mechanism of identifying and disposing aberrant transcripts that lack in-frame stop codons. It is hypothesized that these transcripts are identified during translation when the ribosome arrives at the 3′ end of the mRNA and stalls. Presumably the ribosome stalling recruits additional cofactors, Ski7 and the exosome complex. The exosome degrades the transcript using either one of is ribonucleolytic activities and the ribosome and the peptide are both released. Additional precautionary measures by the nonstop decay pathway may include translational repression of the nonstop transcript after translation, and proteolysis of the released peptide by the proteasome. (4 votes) Priyanka 6 years agoPosted 6 years ago. Direct link to Priyanka's post “It is mentioned in The Ge...” It is mentioned in The Genetic Code, that, AUG codes for methionine, which contains sulfur. In the Hershey-Chase experiment, they made use of the fact that all proteins contain sulfur (because of the presence of methionine, I guess) • (4 votes) tyersome 6 years agoPosted 6 years ago. Direct link to tyersome's post “There are, but this is (u...” There are, but this is (usually) due to removal or modification of the amino-terminal (start) methionine. For example enzymes called "methionine amino-peptidases" cut off this amino acid from the beginning of some proteins — this is an example of what is known as a "post-translational modification". It is also quite common for the first part of a protein (including the starting methionine) to be removed during processing — an example is secreted proteins that have their signal sequences removed during secretion or membrane insertion. Methionines can also be oxidized to form chemically related residues. (4 votes) malekkazar 7 years agoPosted 7 years ago. Direct link to malekkazar's post “Can a DNA end in 3' and t...” Can a DNA end in 3' and the last molecule in this end is a phosphate? Why not?? • (5 votes) Ivana - Science trainee 5 years agoPosted 5 years ago. Direct link to Ivana - Science trainee's post “Phosphate is always attac...” Phosphate is always attached to 5' end, and OH group to 3' end, because of the chemical structure of DNA. (2 votes) ForgottenUser 7 years agoPosted 7 years ago. Direct link to ForgottenUser's post “Why do the number of A's ...” Why do the number of A's on the poly-A tail vary? • (3 votes) leonardodebo 6 years agoPosted 6 years ago. Direct link to leonardodebo's post “Each time a mRNA is read,...” Each time a mRNA is read, an ''A'' of the poly-A tail is cut off, when there's no more ''A'' in the tail, the mRNA can be degraded. A mRNA (let's call it mRNA 1) can have more ''A'' in its tail than another mRNA (mRNA 2) depending on how much the cell needs that product (1 instead of product 2). (5 votes) Jenna Kim 3 years agoPosted 3 years ago. Direct link to Jenna Kim's post “I don't understand: diffe...” I don't understand: difference between non-coding strand, primary transcript, and coding strand? Is the non-coding strand the strand of DNA that isn't used as the template, and the coding strand the strand of DNA that is used as the template? But doesn't both strands of DNA become 'templates' for the RNA, so both of them are coding strands and non-coding strands, depending on which one you're looking at? Thanks in advance. • (3 votes) Shane McGookey 3 years agoPosted 3 years ago. Direct link to Shane McGookey's post “Consider the directionali...” Consider the directionality of the strands to help distinguish between them. One strand runs in the 3' to 5' direction, while the other strand runs in the 5' to 3' direction. This begets the antiparallel structure of the DNA. We refer to the strand that runs in the 3' to 5' direction as the template strand (the template strand is used to transcribe mRNA by matching complementary RNA nucleotides with the nucleotides of the template strand). The strand that runs in the 5' to 3' direction is referred to as the coding strand. Because the 5' to 3' strand is referred to as the coding strand, the template strand (the 3' to 5' strand) can also be referred to as the non-coding strand. The nomenclature is a bit confusing, but hopefully this adds some clarity to the naming. (5 votes)Want to join the conversation?
https://www.khanacademy.org/science/biology/gene-expression-central-dogma/translation-polypeptides/a/trna-and-ribosomes
One codon is a "start" codon that indicates where to start translation. The start codon specifies the amino acid methionine, so most polypeptides begin with this amino acid.
Are there proteins which do not begin with methionine?
