Gene Expression and Regulation 1-2

Class 18

Where is genetic information stored?

In blocks of DNA called genes.

What do genes code for?

They code for mRNA which then codes for proteins.

What determines how a cell will function?

The proteins encoded by genes.

Example: How long is the human insulin gene?

4044 nucleotides on chromosome 1.

What does insulin do?

Signals cells to take up blood sugar.

What is the central dogma?

DNA → RNA → protein.

What is gene expression?

Using gene sequences to make proteins.

What is transcription?

The process of making mRNA from a DNA gene.

What is translation?

Using mRNA to produce a protein.

Which DNA strand is used to make mRNA?

The antisense (template) strand.

Which DNA strand matches the mRNA sequence (except T/U)?

The sense (coding) strand.

Where does transcription occur?

In the nucleus.

Where does translation occur?

At ribosomes in the cytoplasm.

What happens during transcription overall?

DNA is used to make mRNA which exits the nucleus.

What happens during translation overall?

The ribosome reads mRNA and builds a polypeptide which folds into a functional protein.

What are the three differences between DNA and RNA?

RNA has uracil ribose sugar and is single-stranded.

What are the three types of RNA?

mRNA.. rRNA… tRNA.

Function of mRNA?

Carries the genetic "message" copied from DNA.

Function of rRNA?

Forms part of the ribosome structure.

Function of tRNA?

Transfers amino acids to the ribosome during translation.

What structure does tRNA have?

A cloverleaf 2D shape; a folded 3D L-shape.

What is the anticodon?

A three-base region on tRNA that binds complementary mRNA codons.

Where is the amino acid attachment site on tRNA?

At the 3' end.

What do prokaryotes lack that eukaryotes have?

A nucleus.

Why can prokaryotes perform transcription and translation simultaneously?

Because they have no nucleus separating DNA and ribosomes.

Do prokaryotes have introns?

No—they lack introns.

What are the three stages of transcription?

Initiation.. elongation.. termination.

What does RNA polymerase do?

Produces the mRNA copy of DNA during transcription.

Where does RNA polymerase first bind on the DNA?

The promoter region.

What does RNA polymerase build as it moves along DNA?

A complementary RNA strand (mRNA).

When does transcription end?

When RNA polymerase reaches a nucleotide sequence called the transcription terminator.

What is the promoter?

A DNA sequence where RNA polymerase binds to start transcription.

What is the transcription terminator?

A DNA sequence that signals RNA polymerase to stop transcription.

What happens when RNA polymerase reaches the termination sequence?

A hairpin loop forms in the mRNA, causing polymerase and mRNA to detach.

What is the first step of transcription?

RNA polymerase locating the promoter region of a gene.

What is a sigma factor?

A protein that helps RNA polymerase initiate transcription in prokaryotes.

What are transcription factors?

Proteins in eukaryotes that determine which genes are transcribed.

Example of transcription factors in action?

Growth factors trigger transcription of testosterone genes during male puberty.

In which direction does RNA polymerase synthesize RNA?

5' to 3', same direction as DNA polymerase.

What is the template strand?

The DNA strand containing the gene sequence; used as a template to build mRNA.

What is the coding strand?

The DNA strand that has the same sequence as the mRNA (except T instead of U).

Why is the coding strand called the coding strand?

Because its sequence matches the mRNA sequence that encodes the protein.

What happens during termination in transcription?

A hairpin loop forms in the mRNA- releasing polymerase and mRNA from DNA.