Protein synthesis and Mutations Flashcards
How does RNA Polymerase read the DNA strand
- Enzyme
- Only reads DNA strand in a particular direction
What is translation
- The actual construction of the protein
- Requires mRNA; tRNA and ribosomes
- Takes place in cytoplasm in 3 stages
Poly A tail impact
Impacts how long the mRNA strand lasts
Give a brief overview of mRNA; tRNA and ribosomes
- mRNA = carries info in codons for the protein to be formed
- tRNA = transports the amino acids from the pool of amino acids to the site of protein synthesis
- has 3 nucleotides on tRNA ( anticodon ) match the codon on the mRNA ( only the mRNA can determine which amino acid is required )
- Ribosomes = sites of protein synthesis and are composed of 2 subunits
Explain the ribosome fully
- Small unit of the ribosome is present. They are attached to the mRNA near or at the start codon. This assembly is accomplished with the aid of a number of initiation factors.
- The larger ribosomal unit is then added
- In eukaryotes the first amino acid is methionine (AUG), and the initiation factors (proteins) are more complex.
What are the start and stop codons
- Start = Methionine
- Stop = UAA; UGA; UAG
What are the 3 sites present in ribosomes
- A ( amino acide site )
- P ( polypeptide site )
- E ( exit site )
Explain each site fully
- A = position where the new tRNA amino acid complex attaches
- P = position where the growing polypeptide chain is found
- E = position where tRNA is released after releasing its amino acid
Explain initiation in translation
- Occurs in cytoplasm
- tRNA; mRNA; small and large ribosomal units are required
- mRNA = start of polypeptide
- small ribosomal unit = amino acid methionine
( Small ribosomal subunit binds to mRNA; an indicator tRNA with the anticodon UAC pairs with the mRNA start codon AUG. The large ribosomal subunit completes the ribosome. Initiator tRNA occupies the P site. The A site is ready for the next tRNA )
What is the difference between elongation in translation and transcription
- Translation = how amino acids are added in
What do the start and stop codons do
- Start = tells us where translation will start on mRNA strand
- Stop = tells us where to stop ( ensures amino acid chain is the correct length and sequence )
Why is the mRNA; tRNA; rRNA needed
- mRNA = info needed
- tRNA = brings in amino acids into ribosomal unit
-rRNA = physical location
Ho does tRNA link up to mRNA
- On mRNA is a codon which links up to correct anticodon
What tells us which amino acids comes next
Codon
Explain elongation in translation fully
- A tRNA amino acid approaches the ribosome and binds at A-site
- 2 tRNAs can be at a ribosome at one time; the anticodons are paired to the codons
- Peptide bond formation attaches the peptide chain to the newly arrived amino acid
- The ribosome moves forward; the “ empty “ tRNA exits from the E site; the next amino acid - tRNA complex is approaching the ribosome
Explain elongation in translation fully in much more detail
- Peptide bond is formed between the carboxyl end on the last amino acid and the amino-group of the incoming amino acid.
- tRNA on the P-site then releases its amino acid and the ribosome moves along the mRNA to expose the next codon
- First tRNA will now be at the E-site and will be released to get more amino acids, and the growing peptide chain will be at the P-site
- Next codon will code for its amino acid and a new tRNA-amino acid complex will attach to the A-site,
- A peptide bond will form between the last amino acid of the polypeptide chain and the new amino acid
- This process continues until a stop codon is reached
Explain the end of elongation in translation fully
- A stop codon (UAA, UAG or UGA) does not code for any amino acid and this will stop the process of elongation
- A specific protein, called a release factor, will be responsible for breaking the bond between the last amino acid of the polypeptide and its tRNA
- All components will be released and the polypeptide will be modified for its specific function
Explain termination in translation
- The ribosome comes to a stop codon on the mRNA. A release factor binds to the site
- The release factor hydrolyses the bond between the last tRNA at the P site and the polypeptide, releasing them. The ribosomal subunits dissociate
Explain proteins folding correctly after translation
- Newly synthesized proteins cannot perform their function until they fold into their final shapes
- Some regions of the amino acid chain attract or repel other parts, contorting the polypeptide’s overall shape
- Enzymes catalyze the formation of chemical bonds and ‘chaperone’ proteins stabilize partially folded regions
What can illnesses result in
Illness can result from incorrect protein folding, E.G. Alzeimer disease
Explain mutations briefly
- If we change a codon by even 1 nucleotide we might have a issue
- Due to duplications in GC there may be no changes in amino acids
- But if a different amino acid is now coded for, we have a change in the protein
- Can be a + or -
What are the types of mutations
- Substitution
- 3 nucleotide insertions
- 3 nucleotide deletion
- Expanded repeats
- Wild type
- Frameshift
Explain expanded repeat mutations fully
- In an expanded repeat mutation, the number of copies of a three or four nucleotide sequence increases over several generations.
- With each generation the symptoms begin earlier or become more severe, e.g. Huntington disease
Explain base insertion and deletion mutations fully
- One or more nucleotides can be added to or deleted from a gene.
- A frameshift mutation adds or deleted nucleotides in any number other than a multiple of three. This alters the sequence of amino acids and devastates the protein’s function,
Explain nonsense mutations fully
- A base triplet specifying an amino acid changes into one that encodes a stop codon shortening the protein product which influences the organism e.g. cystic fibrosis
Explain missense mutations fully
- Sometimes substitution mutation changes a base triplet so that it specifies a different amino acid, called a missense mutation.
- This may drastically alter protein’s shape and change its function, e.g. sickle cell disease.
Explain silent mutations fully
- Can occur because more than one codon encodes for most amino acids. Such a mutation is silent if the mutated gene encodes the same protein as the original gene version.
Explain substitution mutations fully
- Is replacement of one DNA base with another.
What causes mutations
- Some mutations occur spontaneously, possibly through a DNA replication error,
- Others occur through the exposure to harmful chemicals or radiation that damage the DNA.
- Replication errors occurs when the DNA is replicated during the Cell cycle, cells that divide frequently like those of bacteria may mutate faster, in humans the skin cells replicate often then to have more mutations than cells that do not.
What are mutagens
- Is any external agent that induces mutations
Ultraviolet radiation in sunlight
X-rays
Radioactive fallout from atomic bombs
Nuclear accidents
Chemicals (tobacco or pollutants)
When do mutations occur
- During meiosis. Also, some parts of a chromosome can become inverted or fused with a different chromosome.
