AP Bio Unit 6 - Gene Expression and Regulation

What does semiconservative mean?

Each new strand of DNA has one old strand and one new strand

What is the phosphate terminus of a DNA strand called?

5-prime end

What is the hydroxl terminus of a DNA strand called?

3-prime end

What is the only direction that nucleotides can be added on to a growing DNA strand?

5’ → 3’

In DNA replication, what is the name of the strand that will be synthesized continuously? What about the one synthesized discontinuously (in fragments)?

leading and lagging

What is the role of the enzyme helicase in DNA?

unwinding the DNA

What is the role of the enzyme topoisomerase in DNA?

• it relaxes the super coil at the replication fork

What is the replication fork?

the “V” shaped area where the two strands are separated

What is the role of the enzyme DNA polymerase in DNA?

it synthesizes the new strands

What does DNA polymerase require to initiate synthesis?

RNA primers

What end does DNA polymerase attach to on the template DNA strand? What direction does it build new strands in?

• 3’ end

• 5’ → 3’

What is the role of the enzyme ligase in DNA?

joins the DNA fragments on the lagging strand

What is the order genetic information flows from?

DNA → Pre-mRNA → mRNA → ribosome → Protein

What is transcription?

an enzyme directing the formation of an mRNA molecule

When mRNA is synthesized, how many strands in the double-helix does it use? One or both?

just one, this is known as the template strand

What enzyme synthesizes mRNA?

RNA polymerase

Why is the strand NOT used as the template for mRNA known as the coding strand?

It is in the 5’ → 3’ direction and has the actual genetic code. Since the mRNA wants to have the actual genetic code, it needs to use the mirroring strand as a template.

What are the three types of RNA molecules?

• mRNA (messenger RNA) - carries genetic information

• tRNA (transfer RNA) - brings amino acids to the ribosome during protein creation

• rRNA (ribosomal RNA) - provides structure to ribosomes, allowing them to create amino acids

What does the 5’ cap at the beginning of an mRNA strand help do (3 things)?

• exports mRNA from nucleus to cytoplasm

• protect mRNA from degradation

• help it bind to ribosomes

What is the poly-A tail?

a bunch of adenine added to protect from degradations?

What happens to introns? What happens to exons?

• introns are cutout and removed

• EXons are spliced (stitched) together and EXpressed

What is translation?

the RNA is translated into actual proteins

What are the 3 types of point mutations? (substitutions of one base letter)

Silent mutation - one single letter is replaced, but it doesn’t change the amino acid, usually because its at the third spot and many amino acids work with several combinations (eg. UAA, UAC, UAG)

Missense mutation - one amino acid is different, but it may not affect the entire protein enough to make it non-functional

Nonsense mutation - when one nucleotide letter is changed, accidentally coding for a stop mutation. again, this may not be catastrophic if it is near enough to the end of the code

What is a frameshift mutation?

when a nucleotide is either inserted or deleted, changing every single base letter following it. very catastrophic

What is the lac operon? (in terms of gene regulation by prokaryotes)

• regulates the expression of the lactase gene (ability to digest lactose)

  • is only turned on when lactose is actually in the cell

(important to note that at “status quo” the gene for lactase is blocked and actively repressed by something)

What happens when there is lactose in a cell with lac operon?

• lactose binds to the lactASE repressor

• then, the gene for lactase can now be coded for

What is the trp operon?

when too much trp is produced in the cell, it binds to the inhibitor to prevent further overproduction

What is a histone?

it is the protein that DNA wraps around to form chromosomes

How can histones control gene expression?

• if the histone tightly packs the DNA (unacetylated), the genes will not be coded for

• when the DNA is loosely packed (highly acetylated), the genes are more likely to be coded for