- The RNA enigma
- The RNA engima quiz
- RNA: The basics
- Protein synthesis in the cellular factory
- Protein synthesis in the cellular factory quiz
- Protein synthesis
- The RNA origin of life
- The RNA origin of life quiz
- RNA world
- Virus wars
- Virus wars quiz
Transfer RNA (tRNA)
Transfer RNAs (tRNAS) have two jobs: 1. They carry a protein building block (an amino acid) to a cell's protein assembly machine, called a ribosome. 2. They translate the genetic code of messenger RNA (mRNA) into the amino acid sequence of proteins.
tRNAs fold up into an upside-down L shape. The top end of the L has an amino acid bound to it, and the bottom end has three bases (nucleotides) that bind to mRNA when a protein is made. mRNA carries the genetic code for a protein in a sequence of nucleotides. Every three nucleotides of mRNA are recognized by a particular tRNA that carries a particular amino acid.
When making a protein, the ribosome holds mRNA in place. When a tRNA enters the ribosome, it binds to a complementary section of mRNA. At this moment, the tRNA releases its amino acid to be incorporated into a growing chain of amino acids that will become a protein. The empty tRNA leaves the ribosome to make space for another amino acid-carrying tRNA.
RNA Cutter (RNase)
RNA cutters, or ribonucleases (RNases), are enzymes made of RNA that break down other RNA molecules by chopping them up into smaller pieces.
RNases perform many roles, including: getting rid of unwanted RNA, refining RNA molecules by chopping off unwanted sections of RNA, and serving as a first defense against infection from RNA viruses by breaking down viral RNA.
RNases work like recycling plants. They stop cells from accumulating unwanted RNAs by breaking them down into pieces that can be recycled into new RNA molecules.
There are two types of RNase: the first bites off one nucleotide at a time from the ends of an RNA molecule; the other works in the middle of an RNA molecule, splitting it apart or chopping out chunks of RNA.
RNases break down all the unprotected RNAs that they encounter in a cell. An RNA can protect itself from RNase attack by forming complexes with proteins or by adding particular chemical groups to either of its ends. And an RNase can be stopped in its tracks when an RNase inhibitor protein binds to it.
All living things that have been studied contain RNases. So, RNases must have evolved in early life-forms and been conserved through evolution. This tells us that breaking down RNA is a very important process.
Ribosomes and rRNA
Ribosomes are a cell’s protein-assembly machines. Their job is to link protein building blocks (amino acids) together to make proteins in an order spelled out in messenger RNA (mRNA).
Ribosomes are made of two parts: a small subunit and a large subunit. These subunits are made of ribosomal RNA (rRNA) and proteins.
When making a protein, the small ribosome subunit holds mRNA in place. Transfer RNAs (tRNA) enter the ribosome carrying individual amino acids. The large ribosome subunit bonds these amino acids together to make a protein. When a tRNA releases its amino acid, it exits the ribosome and another tRNA takes its place to add its amino acid to the growing protein. When a ribosome finishes translating an mRNA, the small and large ribosome subunits split apart.
It’s the rRNA in the ribosome that links amino acids together when making a protein, which means that rRNA is an RNA enzyme. The role of the ribosome proteins seems to be to stabilize the ribosome structure.
All living things that have been studied contain rRNA. So rRNA must have evolved in early life-forms and been conserved through evolution. Evolutionarily speaking, rRNAs are far older than the proteins in a ribosome. This suggests that in very early life-forms, ribosomes operated without proteins to stabilize them.
This is good evidence for the RNA World hypothesis, which suggests that RNA allowed life to form on Earth, and that it came before DNA and proteins. Evolution of rRNA as a cell’s protein-assembly machine would have made the existence of proteins possible.
mRNA-splicing machines chop out unwanted sections of newly made messenger RNA (mRNA) to create mature mRNA that can be translated to make a protein.
When a strand of mRNA is first copied from DNA, the genetic code it carries isn’t ready to be translated to make a protein. First, it needs to be edited by a machine made of RNAs and proteins, called a spliceosome. It’s like an editor that proofreads the first draft of an mRNA. Like scissors and glue, it chops out unwanted sections of mRNA, called introns, and sticks the remaining pieces back together again. This is called splicing.
A single mRNA copied from one gene can code for lots of different proteins if it’s spliced in different ways. This explains how humans are able to produce about 100,000 proteins from only about 20,000 genes.
Want to join the conversation?
- I don't quite understand the whole process of Protein Synthesis.
:/ help?(9 votes)
- 2 subuntis of ribosomes hold a mRNA (messenger) so the tRNA (transport) can bring amino acids to the large ribosome subunit so he can make the protein (using his rRNA) . When the protein is made they fall apart and go their seperate ways.
The small ribosome is there just to help hold the mRNA while the bigger one is there to hold and create the protein using the amino acids (the building blocks of the protein) and his ribosomal RNA along with the help of the tRNAs which bring and help build the protein.
Still confused? Ask about the part you're confused and I'll try and help you :)(30 votes)
- The article states that in protein synthesis, every three nucleotides of the mRNA is recognized by a specific tRNA. Does the cell have an efficient way of speeding up the process of finding the right tRNA for the sequence of mRNA? Or does it just randomly go through each tRNA until it finds the right one?
For example, let's say I had a standard 52 card playing deck, and gave one card each to 52 people. I then want to look for the person with the queen of hearts. I could randomly ask each of the 52 possible people what card they have until I find the right person. Or I could first group people based on suit and then only talk to a maximum of 13 people with a card of a heart suit.(8 votes)
- How does it finish off making the Protein?(3 votes)
- In the process of translation, mRNA is between two subunits- large and small. There are two attachment sites, and tRNA moves along those, and eventually starts coding messages the mRNA has, so amino acids are provided to the ribosomes. Since mRNA is continuously being feed through a small and large subunit, and there is a peptide bond being formed, protein is being made. Then, when a stop codon is reached, protein is finished off and ready. A stop codon is what stops the process, essentially.(3 votes)
- What's the difference between mRNA-splicing and RNA cutters, or ribonucleases (RNases)? It seems like they are similar in that they both "refin(e) RNA molecules by chopping off unwanted sections of RNA"(2 votes)
- RNases are recycling tools, they destroy RNA strands and are as a general rule not very specific. They see (unprotected) RNA, they chomp down on it.
mRNA - splicing RNA-enzymes are part of a specific machinery, that carefully and specifically for certain signals removes parts of a mRNA-strand without destroying the strand. Without the action of this machinery, the Spliceosome, the Ribosome could not make the correct protein from the mRNA, since there would be additional code in the strand messing with the translation into protein.(2 votes)
- How can an RNA defeat cancer?(1 vote)
- I read somewhere that the subunits of ribosomes are named (for e.g 40s,30s) So what do they signify?(0 votes)
- The 40s or 30s signify a designation known as a Svedberg Unit. These particles are very small and putting a ruler next to them isn't practical. A Svedberg Unit is a measuring system for small particles. When fluid is spun in a centrifuge, particles in that fluid will seperate and settle. The speed at which different particles settle to the bottom is a function of size. The time can be measured and from that a measurement assigned that relates to size. This is what the 's' designations signify.(3 votes)
- i 've watch lots of video in khan academy, but i am still confused
does one mRNA account for one gene ?
does one mRNA account for one protein ?
does one gene account for one protein ?(1 vote)
- I'm not sure about the first two but I think one gene doesn't account for just one protein because the gene can code for different proteins if it's spliced in a different way.(0 votes)
- If asked to explain the role of the different RNA (mRNA, tRNA, rRNA) how would you do that?(0 votes)
- Messenger-RNA is the messenger obviously, between the nuclear and a ribosome. It gets the message from a DNA and goes outside the nuclear. Then a ribosome can read it.
Transfer-RNA transfers one of the 20 amino acids to the ribosome so the ribosome can create an amino-acid strand.
Ribosome-RNA is the part of the ribosome. Another ribosome-RNA is the other part of the ribosome. The ribosome makes the peptide bond/amide bond of the amino acids.
Someone can correct me if I'm wrong.(2 votes)