From Gene to Protein Flashcards
DNA Sequence
Transcription
DNA sequence of a gene is copied to make an RNA molecule
One of the two DNA strands, the template strand, provides a template for ordering the sequence of complementary nucleotides in an RNA transcript
DNA Sequence
Translation
sequence of the mRNA is decoded to specify the amino acid sequence of a polypeptide
Codons
The nucleotides of the mRNA are read in triplets (groups of three) called codons
Codon Count:
There are 61 codons that specify/encode amino acids and only 20 different amino acids, so the genetic code is redundant
Reading Frame
way of dividing the sequence of nucleotides in a nucleic acid (DNA or RNA) molecule into a set of consecutive, non-overlapping triplets
it’s a codon chart.
RNA Synthesis catalyzed by:
RNA polymerase
The DNA sequence where RNA polymerase attaches is called the promoter
Transcription
What is the RNA strand complementary to?
The RNA is complementary to the DNA template strand
Transcription Unit
The stretch of DNA that is transcribed
RNA Processing
Enzymes in the eukaryotic nucleus modify pre-mRNA (RNA processing) before the genetic messages are dispatched to the cytoplasm
Introns
Most eukaryotic genes and their RNA transcripts have long noncoding stretches of nucleotides that lie between coding regions = introns
These are removed through RNA splicing
Exons
a segment of a DNA or RNA molecule containing information coding for a protein or peptide sequence.
The other regions are called exons because they are eventually expressed, usually translated into amino acid sequences
Messenger RNA (mRNA)
Genetic information flows from mRNA to protein through the process of translation
Genetic information flows from mRNA to protein through the process of translation
Transfer RNA (tRNA)
tRNAs transfer amino acids to the growing polypeptide in a ribosome
- Genetic information flows from mRNA to protein through the process of translation
- Each tRNA molecule enables translation of a given mRNA codon into a certain amino acid
- Each carries a specific amino acid on one end
- Each has an anticodon on the other end; the anticodon base-pairs with a complementary codon on mRNA
Ribosome
- perform biological protein synthesis
- link amino acids together in the order specified by the codons of mRNA molecules to form polypeptide chains
A ribosome has 3 binding sites for
tRNA:
* P site holds the tRNA that carries the growing polypeptide chain
* A site holds the tRNA that carries the next amino acid to be added to the chain
* E site is the exit site, where discharged tRNAs leave the ribosome
When are polypeptide chains modified?
Polypeptide chains are modified after translation or targeted to specific sites in the cell
Protein Folding
During synthesis, a polypeptide chain begins to coil and fold spontaneously into a specific shape: a three-dimensional molecule with secondary and tertiary structure
A gene determines the primary structure, and the
primary structure in turn determines shape
Where does polypeptide synthesis begin?
Polypeptide synthesis always begins in
cytosol
Cytosol
Cytosol
the aqueous component of the cytoplasm of a cell, within which various organelles and particles are suspended
Signal Peptide
Polypeptides destined for the ER or for secretion are marked by a signal peptide
Signal-Recognition Particle (SRP)
A signal-recognition particle (SRP) binds to the signal peptide
SRP escorts the ribosome to a receptor protein built into the ER membrane
Silent Mutations
Have no effect on amino acid produced by a codon because of redundancy in the genetic code
Missense Mutations
Still code for an amino acid, but not the correct amino acid
Nonsense Mutations
Change an amino acid codon into a stop codon
