Transcription and Translation

What is the difference between RNA and DNA

RNA has Uracil, is single stranded, and a ribose sugar while DNA has Thymine, is double stranded, and a deoxyribose sugar

Where does transcription take place?

Nucleus

Where does translation take place?

In the cytoplasm, specifically ribosomes

What is the first step of transcription?

Initiation: RNA polymerase attaches to the promotor and RNA polymerase starts synthesizing. RNA polymerase unwinds the DNA and adds complementary RNA nucleotides to build an mRNA molecule.

What is the second step of transcription?

Growth: the newly formed RNA strand grows. As synthesis continues, the growing RNA molecule peels away from its DNA template, allowing the two separated DNA strands to come back together in the already transcribed region

What is the third step of transcription?

Termination: RNA polymerase reaches the terminator DNA (signaling the end of a gene). The polymerase molecule detaches from the newly made RNA strand and gene. The mRNA in eukaryotes are then capped before leaving the nucleus through the pores of the cytoplasm (so they don’t fall apart)

What is the first step of translation?

Initiation: ribosomes bind to mRNA and then tRNA (carrying Met) binds to the start codon at the ribosome’s P-site. The large ribosomal subunit binds with the small ribosomal subunit to form the initiation complex

What is the second step of translation?

Elongation: tRNA brings corresponding amino acids to the A site (to bind with mRNA codons). The ribosome acts as an enzyme to form a peptide bond between the amino acid in the A site and the growing polypeptide chain at the P site. Ribosomes move one codon forward on the mRNA

What is the third step of translation?

Termination: the ribosome reaches a stop codon and the newly formed polypeptide chain is released from the tRNA

Codon

A sequence of three consecutive nucleotides (a triplet) in DNA or mRNA that specifies a particular amino acid or signals the start/stop of protein synthesis

Anticodon

A three-nucleotide sequence located on a transfer RNA (tRNA) molecule that is complementary to a specific codon on messenger RNA (mRNA)

mRNA

Messenger RNA that conveys genetic messages from DNA to the translation machinery of the cell

tRNA

Transfer RNA, a molecular interpreter for the codons

rRNA

Ribosomal RNA, makes up the subunits of ribosome

RNA splicing

The cutting-and-pasting process. Introns are the internal noncoding regions and the coding regions (parts of a gene that are expressed) are called exons. Allows one gene to produce multiple protein variants

P site

Holds the growing polypeptide

A site

tRNA binding site, ready for the next amino acid

Silent mutation

A type of genetic point mutation that changes a nucleotide in a DNA codon but does not alter the resulting amino acid sequence in a protein

Missense mutation

A point mutation where a single DNA nucleotide change results in a different amino acid being incorporated into a protein

Nonsense mutation

A nonsense mutation is a point mutation in DNA that changes an amino acid codon into a premature stop codon

Frame shift mutation

A genetic mutation caused by the insertion or deletion of a number of nucleotides not divisible by three in a DNA sequence

Promotor vs. terminator

Promoter is the binding site for RNA polymerase. The terminator is a sequence of bases that marks the end of a gene.

The 5’ Guanine cap

A modified guanosine nucleotide added to the 5' end of eukaryotic pre-mRNA immediately after transcription initiation. Linked via a unique 5′-5′ triphosphate bridge, this cap protects mRNA from degradation by exonucleases

The poly(A) tail

A long chain of adenine nucleotides added to the 3' end of eukaryotic mRNA. It enhances stability, protects mRNA from premature degradation, and aids in nuclear export and translation efficiency.