transcription & translation quiz

what does the central dogma do?

• The central dogma explains the flow of genetic information in a cell: DNA → RNA → Protein.

• It describes how DNA is transcribed into RNA, and RNA is translated into proteins, which carry out the cell’s functions.

Amino acid chains are built in the

cytoplasm

DNA instructions are in the

nucleus

Why would the cell NOT want to send the DNA instructions for building proteins out into the cytoplasm?

DNA is too valuable and vulnerable

Protection of genetic information: DNA contains all the instructions for the cell. If it left the nucleus, it could be damaged by enzymes, chemicals, or radiation.

Maintaining control: The nucleus acts as a secure space, allowing the cell to regulate which genes are copied into RNA and when.

Efficiency: Instead of moving the large DNA molecules, the cell makes RNA copies (mRNA) of the needed instructions. mRNA is smaller, temporary, and can travel to ribosomes in the cytoplasm to make proteins.

What are the 3 most important types of RNA involved in transcription and translation?

mRNA, tRNA, and rRNA

what is messenger RNA (mRNA)?

• It carries the genetic instructions for making a specific protein from the DNA (in the nucleus) to the ribosome (in the cytoplasm).

• The ribosome then "eads the mRNA sequence in three-base sections (codons) to correctly assemble amino acids into a protein chain (a process called translation)

what is tRNA?

tRNA (transfer RNA) is a small RNA molecule responsible for carrying specific amino acids to the ribosome

• It has an anticodon sequence that is complementary to a codon on the mRNA.

• It ensures the correct amino acid is added to the growing protein chain during translation.

what is rRNA?

Makes up the ribosomes

What is transcription?

the process of making RNA from a DNA template

How does transcription work?

• Initiation: RNA polymerase opens double helix and binds to the promoter site (start codon which is a 3 nucleotide sequence at the beginning of gene). 

• Elongation: RNA polymerase reads the DNA template (3’ to 5’) and forms the new mRNA (5’ to 3’) using the nucleotide bases (Adenine, Uracil, Guanine, and Cytosine). Only one DNA strand is used as a template.

• Termination: RNA polymerase recognizes the stop codon (end of gene)

the mRNA transcript releases from the DNA and enters the cytoplasm

What is the promoter site?

a specific DNA sequence located upstream of a gene that acts as a binding site for the RNA polymerase

It signals the beginning of a gene and initiates the process of transcription (copying DNA into RNA).

What is the TATA box?

indicator of where translation starts (starts after the TATA box)

Parts of a gene: exons and introns

exons: code for amino acids

introns: portions that do NOT code for amino acids and are removed from the mRNA before translation

Post-transcription

• 5’ cap (7-methyl guanosine) is added after transcription

• poly (A tail) (200 adenine) is added to the 3’ end

• this protects mRNA from degradation when exiting the nucleus

sense vs antisense strand

antisense: DNA strand that’s used to make the mRNA

sense: other DNA strand

codons & their function

• 3 nucleotides that code for an amino acid

• only 61/64 codons are used to specify which of the 20 amino acids are added

• multiple codes for one amino acid

• There are 3 codons that don’t code for an amino acid, these mark the end of the protein and stop the addition of amino acids to the end of the protein chain

characteristics of the code

• genetic code is the same for all living things

• the same RNA corresponds to the same amino acids in all living organism

• evidence that all organisms on Earth shared a common ancestor

what does the anticodon do in translation?

The anticodon is a sequence of three nucleotides on tRNA that pairs with the complementary codon on mRNA, ensuring the correct amino acid is added to the growing protein.

what are E, P, and A sites?

• A site (Aminoacyl site): Where a new tRNA carrying an amino acid enters.

• P site (Peptidyl site): Where the tRNA holds the growing polypeptide chain.

• E site (Exit site): Where the tRNA, now without an amino acid, exits the ribosome.

translation steps

initiation: The small ribosome subunit binds to the 5’ end of mRNA, moves to the start codon (AUG), and joins with the large subunit and the first tRNA.

elongation: tRNAs bring amino acids to the ribosome, and peptidyl transferase links them into a chain as the ribosome moves along the mRNA

termination: The ribosome stops at a stop codon, and the completed protein is released.

how is translation different in eukaryotes

Eukaryotic ribosomes are bigger and more complex, and transcription happens in the nucleus while translation happens in the cytoplasm.