Lecture 3: Transcription and Translation Flashcards
Gene expression
The process by which DNA directs protein synthesis
Roles of Proteins
Structural: membranes and organelles
Enzymes: carry out essential reactions
Receptors: proteins that bind to other molecules such as hormones to relay signals inside the cell
Hormones: proteins that are used for the cell to cell communication
Antibodies: destroy foreign materials
Central Dogma of Molecular Biology
Concept that cells are governed by a cellular chain of command
DNA -> RNA -> Protein
Proteins
Links between genotype and phenotype
Transcription
DNA strand serves as a template for the synthesis of a complementary RNA strand
Translation
Polypeptide is synthesized using mRNA as a template
mRNA (messenger RNA)
Encodes amino acid sequence of a polypeptide
tRNA (transfer RNA)
Brings amino acids to ribosomes during translation
rRNA (ribosomal RNA)
With ribosomal proteins, makes up the ribosomes, the organelles that translate the mRNA
snRNA (small nuclear RNA)
With proteins forms complexes that are used in RNA processing in eukaryotes
RNA Polymerase
Separates the DNA strands and joins the RNA nucleotides together as they base-pair with the DNA template
Promoters
Are the specific sequence of DNA in a gene where transcription is initiated
Poly (A) Tail
Consists of multiple adenosine monophosphates; in other words, it is a stretch of RNA that has only adenine bases
Polyadenylation
In eukaryotes part of the process that produces mature messenger RNA (mRNA) for translation
Splicosome
Complex of small RNAs
Alternative RNA Splicing
- Genes that can encode more than one kind of polypeptide depending on which segments are treated as exons during pre-mRNA splicing
- Alternative splicing increases the number of different proteins an organism can produce is greater than genes
Non-Coding RNA
Are a variety of small RNAs that perform diverse regulatory roles such as ribozymes, microRNAs, etc. Before it was assumed that most DNA that doesn’t code for proteins, rRNA, or tRNA was transcribed.
Codons
- Triplets of nucleotide bases that code for an amino acid. Codons are read in the correct reading frame (starting with AUG) in order for the specified polypeptide to be produced.
- 64 codons 4^3: 61 code for amino acids and 3 are stop codons
- AUG (Met) is the start codon
Transfer RNA (tRNA)
- each transfer RNA is specific for one amino acid and for a particular codon in mRNA
- anticodon in the tRNA is complementary to the mRNA codon
- anticodon determines which amino acid is attached to the tRNA
- family of tRNA molecules enables the codons in a mRNA molecule to be translated into the sequence of amino acids in the protein
Anticodon
Complementary to the mRNA codon
Wobble
Flexible pairing at the third based of a codon that allows some tRNAs to bind to more than one codon
Shine-Dalgarno Sequence
Ribosomal binding site in bacterial and archaeal messenger RNA, generally located around 8 bases upstream of the start codon AUG
Ribosomes
- This is where translation occurs, it consists of two subunits- a large and a small that are both made of proteins and ribosomal RNA (rRNA)
- They facilitate specific coupling of tRNA anticodons with mRNA codons during protein synthesis
- Ribosomes have a binding site for mRNA and three binding sites for tRNA
P Site (peptidyl-tRNA site)
Is the binding site of initiator tRNA-Met and holds the tRNA carrying the growing polypeptide chain
A Site (aminoacyl-tRNA site)
Holds the tRNA with the next amino acid to be added to the chain
E Site (exit)
Is where empty (uncharged) tRNAs leave the ribosome
Non-Coding RNA
Are a variety of small RNAs that perform diverse regulatory roles such as ribozymes, microRNAs, etc. Before it was assumed that most DNA that does n;t code for proteins, rRNA, or tRNA were transcribed.
