DNA, genes and protein synthesis - Chapter 8 Flashcards
What is a gene ?
A section of DNA that codes for a specific sequence of amino acids which make up the primary structure of a protein
Allele ?
Alternative form of a gene
Name the 4 features of a genetic code?
- It is a triplet code
- It is a degenerate code
- It is a non-overlapping code
- It is a universal code
What does triplet code mean?
3 bases that codes for one amino acid
What is a codon?
3 bases ( a triplet)
What is a degenerate code?
When more than one triplet codes for an amino acid
What is a non-overlapping code?
Look at notes for example
Each base appears in one triplet , only read each base one
What is a universal code ?
The same codon always codes for the same amino acid
What is transcription (definition)?
The process of producing pre-mRNA using a sequence of DNA as a template
Where does transcription take place?
In the nucleus
What is splicing (definition) ?
The process of removing introns from pre-mRNA because they don’t code for an amino acid
Where does splicing take place ?
In the nucleus
What is translation ?
The production of a polypeptide chain
Where does translation take place?
In the ribosomes
What is mRNA (messenger RNA) ?
Copy of a gene used to code for a polypeptide
What is tRNA (transfer RNA) ?
A clover- leaf shaped sequence of bases. It carries amino acids during translation.
What is rRNA (ribosomal RNA) ?
A primary component of ribosomes
Transcription steps?
- DNA in the nucleus
- DNA helicase breaks the hydrogen bonds
- RNA polymerase binds to the start of a gene (section of DNA) and unwinds the double helix, exposing one of the template strands.
4.Free RNA nucleotides bind to free DNA nucleotides on template strand via complementary base pairing. Adenine to uracil, and cytosine to guanine.
This is formed via phosphodiester bonds in a condensation reaction (due to RNA polymerase) - Behind the RNA polymerase, the DNA rejoins into a double helix
- RNA polymerase reaches a terminator ( a stop codon ), the chain is terminated, the pre- mRNA detaches and double helix reforms
- Introns are removed due to splicing, so mRNA is formed.
What are exons?
Coding regions
What are introns?
Non -coding regions
Splicing steps?
Spliceosome forms and causes the introns to form loops which allows exons to be joined under the loop, and allows the introns to be removed.
Splicing occurs in _______ cells, but not ________ cells. Why?
Splicing occurs in eukaryotic cells, but not in prokaryotic cells. This is because the RNA produced in eukaryotes has introns. But prokaryotic cells do not have introns when RNA is produced
What is a histone ?
Proteins that the DNA coils around forming supercoils, which makes DNA more compact
Prokaryotic vs Eukaryotic DNA
Prokaryotic : short, circular DNA molecules, not associated with proteins (no histones)
Eukaryotic: long, linear DNA molecules, associated with proteins (has histones)
Translation steps?
After splicing, mRNA attaches to the ribsome ( no longer pre-mRNA)
- tRNA carries amino acids to the ribosome
Each tRNA has an anticodon (a triplet of RNA bases) that is complementary to a codon on the mRNA strand - The mRNA attaches to the ribosome. Specific tRNA molecule for specific amino acid
- The mRNA will be fed through the ribosome and the RNA bases are read in sequence
- The amino acids are carried to the ribsome by tRNA, and the anticodon on the tRNA attach to complementary bases on the mRNA. The amino acids become connected by peptide bonds and are released as a chain.
ATP is required to make these peptide bonds. - tRNA is released after amino acid joined to polypeptide
- Ribosome moves along the mRNA to form the polypeptide.
When the end of the sequence is reached, the newly formed polypeptide chain is released from the ribosome and folded and a protein forms
What is required to make these peptide bonds ?
ATP
What is the proteome of a cell ?
The proteome is the number of different proteins that a cell is able to produce / DNA is able to code for
