Module 1.4 RNA and Gene Expression Flashcards
Central Dogma
DNA transcribed into RNA
RNA translated in amino acid chain
Amino acid chain folded in protein
Chemical Nature of RNA
Structural components
- RNA contains the sugar ribose with an –OH group at 3’ AND 2’ carbons (ribose vs deoxyribose)
- RNA contains the base uracil instead of thymine. Uracil as -H instead of -CH3 (methyl group)
- Uracil base-pairs with adenine (2 hydrogen bonds)
Mostly single-stranded
Types of RNA
Messenger RNA (mRNA)
function
RNA that encodes proteins
transcribed from protein-coding genes
all other RNA types are transcribed from non-protein coding genes
Types of RNA
Transfer RNA (tRNA)
RNA that acts as an adapter between mRNA and amino acids
selects amino acids and hold them in place on a ribosome
Types of RNA
Ribosomal RNA (rRNA)
function
RNA that forms the ribosome, the main machinery for protein synthesis
Types of RNA
Small nucleolar RNA (snoRNA)
function
RNA that facilitates chemical modification of RNAs
Types of RNA
MicroRNA (miRNA)
function
RNA (smaller transcript) that regulates gene expression
Types of RNA
Small interfering RNA (siRNA)
function
RNA that silences gene expression
Types of RNA
Long non-coding RNAs (lncRNA)
function
RNA (longer transcript) that regulates gene expression
Genetic Codon
Stop Codons
3
UAA
UAG
UGA
transcription
copy portion of DNA to RNA
gene
sequence of DNA nucleotides transcribed to produce a functional RNA
protein functions
cellular structure
enzymatic activities
hormonal regulation
signaling molecules
transportation
etc…
protein-coding genes
Genes that encode information used to specify the linear order of amino acids for every protein the organism makes
non protein-coding genes
Genes that encode RNAs that have structural and catalytical roles in the cell
can fold into 3D structures like proteins
RNA polymerase
enzyme that mediates transcription
catalyzes formation of phosphodiester bonds of RNA chain stepwise along one of strand of DNA
RNA polymerase
active site
Location in RNA Polymerase that unwinds DNA helix
Transcription
ribonuclesoide triphosphates
Added to RNA strand by RNA polymerase as nucleoside monophosphates (eg. AMP) through high-energy hydrolysis. Ribose instead of deoxyribose (dAMP)
ATP
GTP
CTP
UTP
DNA replication vs Transcription
3 differences
- RNA doesn’t stay hydrogen-bound to DNA (RNA exit channel)
- RNA molecules shorter (< few thousand) than DNA (250 million)
- RNA polymerase can start chain without a primer
small nuclear RNA (snRNA)
Functions in various nuclear processes (eg. splicing)
directs splicing of pre-mRNA as part of maturation process
Genetic Codon
Rules for translating mRNA to amino acids based on 3-nucleotide sequences
start codon
code and amino acid
AUG
Methionine
M
tRNA structure
size, components
~80 nucleotides in clover leaf secondary structure
Loops: T, D, Anticodon with 3 base pairs
Amino acid matching anticodon bp attached at 3’ end of tRNA
tRNA + amino acid = charged tRNA
amino acid tRNA synthetase
enzyme that couples an amino acid to a tRNA molecule with its corresponding anticodon
Ribosome structure
large and small subunit each composed of one or more rRNA + ribosomal proteins
N-terminal
protein structure
end of a protein synthesized first
initiator tRNA
tRNA that codes for methioninie (AUG) but has a different sequence than a regular methionine tRNA
this methionine usually removed later by a specific protease
Translation
process
- Initiator tRNA binds to mRNA
- Small ribosomal unit binds at start codon site
- Large ribosomal subunit binds and begins elongation
- Charged tRNA sequentially binds to A, P, and E ribosomal sites
Ribosomal binding sites
- A (aminoacyl): tRNA binding
- P (peptidyl): peptide bond formation (connect amino acids)
- E (exit) tRNA ejection when ribosome moves along mRNA
Codon
3 mRNA nucleotide code that translates to specific amino acid
Amino acids tend to have the same 1st and 2nd nucleotide for their codons
C-terminal
end of a protein synthesized last
