Biol 1057 - From DNA to protein Flashcards
Briefly define DNA and chromosomes
DNA =
- Polynucleotide double helix structure of a sequence of base pairs
- Means by which genetic information passes from generation to generation
Chromosomes =
- DNA molecules associated with proteins called histones
Briefly define genes
- Sections of DNA that contain coded information for making functional RNA and
polypeptides - One DNA molecule carries many genes
- Located in a particular position (locus) on the DNA
Outline the strucuture of DNA
- Double helix structure with 2 polynucleotide chains held together by hydrogen bonds through condensation eactions
(Between complementary bases)
ADENINE & THYMINE - 2 hydrogen bonds
CYTOSINE & GUANINE - 3 hydrogen bonds
Outline a triplet
- The code has 3 bases for each amino acid and each one is called a triplet (64 possible triplets)
- Some amino acids are coded for by more than one triplet
Outline RNA
- Single polynucleotide chain which is relatively short
- Nucleotides are the monomores
Outline what a promoter region is
- DNA sequence that signals the start of
the gene. - The promoter is recognized by
enzymes involved in transcription
Outline the process of transcription
DNA - MRNA
INITIATION
- Unzipping of DNA double helix, RNA polymerase binds to DNA promoter ;
- Hydrogen bonds between DNA bases break and one DNA strand acts as a template
ELONGATION - RNA polymerase moves along the
DNA template strand in a 3’-to-5’ direction. It adds free RNA nucleotides only to the 3’ end. The RNA chain grows - Complementary base pairs formed A-T C-G G-C
Uracil replaced with Thymine in RNA A-U
TERMINATION - DNA contains a terminator
sequence. When RNA polymerase reaches the terminator sequence, detaches from the
template strand and releases the pre-mRNA. - forms Pre-mRNA which is spliced to form mRNA to remove introns
Outline the reasons for splicing
- Protects from
degradation - Regulates nuclear
export - Promotes ribosome
binding
Describe where translation takes place in eukaryotes and prokaryotes.
Cytoplasm of ribosomes
Outline what tRNA is
- Small, clover-shape molecule with up
to 80 nucleotides - Each tRNA has an anticodon that is
specific to that one amino acid
Outline what a codon is
Codon = sequence of three bases on
mRNA
* A Codon codes for a single amino
acid
Outline a ribosome
- Consists of a small (~30S) & a large
(~50S) subunit - Has an mRNA binding site
- Has 3 tRNA binding sites
A: aminoacyl
P: peptidyl
E: exit - Made of proteins & ribosomal RNA
(rRNA)
Outline the process of translation1
Translation Initation
1. mRNA attaches to the ribosome in the cytoplasm and ribosome moves to find the start AUG codon on small ribosomal subunit
2.
- The anticodon of an incoming aminoacyl tRNA base-pairs with the complementary mRNA codon in the A site. Hydrolysis of GTP increases the accuracy and efficiency of this step
- Peptide bond formation. An rRNA molecule of the large Subunit catalyzes the formation of a peptide bond between the new amino acid in the A site and the carboxyl end of the growing polypeptide in the P site. This step attaches the polypeptide to the tRNA in the A site
- Translocation. The ribosome translocates the tRNA in the A site to the P site. The empty tRNA in the P site is moved to the E site, where it is released. The mRNA moves along with its bound tRNAs, bringing the next codon to be translated into the A site
Outline the process of translation 2(Termination)
- When a ribosome reaches a stop codon on mRNA, the A site of the ribosome accepts a protein called a release factor instead of tRNA.
0 - The release factor hydrolyzes the bond between the tRNA in the P site and the last amino acid of the polypeptide chain.
The polypeptide is thus freed from the ribosome. - The two ribosomal subunits and the other components of the assembly dissociate
