(WIP) AP Biology - Unit 6

Nucleic Acid

Polymer. [This] stores genetic information in biological systems & creates DNA and RNA.

Nucleotide

Monomer, Phosphate + sugar + nitrogenous base. Building block of DNA and RNA.

Nitrogenous bases

The “code” of DNA.

(A, C, T, U & G)

Purines

Organic compound (nitrogenous base), Double ring structure.

6+5 membered ring. Has a pyrimidine ring fused with an imidazole ring.

Pyrimidines

Organic compound (nitrogenous base), 6 membered ring

Nitrogen atoms at 1 and 3 positions.

Hydrogen Bonds

A weak bond between two molecules.

From an electrostatic attraction between a proton in one molecule and an (electro)negative atom in the other.

Complementary Base Pairs

A+ T/U form 2 hydrogen bonds.

G + C form 3 hydrogen bonds.

These are examples of [this.]

(Helpful remembering technique: Apples to trees, cars to garages)

Anti-parallel

DNA strands can only bond if ordered in [this] way.

Direction of a strand is based on the 5’ end and the 3’ end. (3’ = free to bond)

Plasmids

Small circular (double-stranded) pieces of DNA, different from chromosomal DNA.

Mainly found in bacteria.

DNA is synthesized in the [] direction?

This is synthesized in the 5’ to 3’ direction.

Why is replication a “semiconservative” process?

In [this] process, one strand of DNA serves as a template for a new strand of complementary DNA.

It conserves “half" of the DNA.

Helicase’s job

[This enzyme] unwinds the DNA strand into two strands. (the 3’ and 5’ strands)

“Unzips” the DNA.

Topoisomerase’s job

This enzyme changes the (physical) state of DNA (between relaxed & supercoiled, linked and unlinked, etc) in front of the replication fork to repair DNA problems.

This enzyme fixes topological issues.

Supercoiling

When DNA coils more tightly than usual.

Replication fork

A Y-shaped structure made in DNA replication where two strands of DNA are separated & replicated.

Polymerase

[This enzyme] synthesizes polymers and makes new copies of DNA.

“Lagging strand”

[This strand] is the one that is synthesized in the opposite direction of the Replication Fork.

This one is replicated discontinuously.

Okazaki fragments

Short DNA sequences synthesized discontinuously during DNA replication.

Forms the “lagging strand.”

Leading Strand

[This strand] is replicated continuously.

How does topoisomerase “fix” DNA?

This enzyme fixes DNA by binding to it and cutting the sugar-phosphate backbone of either one or both of the DNA strands. This break allows the DNA to be untangled or unwound (releases the tension). At the end of these processes, the DNA backbone is resealed.

This fixes topological problems!

Difference between type 1 and type 2 topoisomerases?

type I topoisomerases: cuts one backbone of DNA

Type 2: cuts both of the DNA strands.

Steps of Transcription (3)

Initiation (start), Elongation (build), Termination (stop)

Basically: starts, does its thing, then stops.

In DNA, each strand (5’ 3’ and 3’ 5’ individually) can be referred to as…

5’ 3’ is the: Non-template/ Sense/ Coding strand

3’ 5’ is the: Template/ Antisense/ Non-coding strand (transcribed strand)

When 5’ 3’ undergoes transcription, it becomes…

[this strand] becomes mRNA, which is the same as [this strand], except the T’s have become U’s!

New nucleotides are built in [this] direction.

These are built in the 5’ 3’ direction!

What direction does the RNA polymerase read the template (5’ 3’) strand?

[This enzyme] builds in the 3’ to 5’ direction!

Introns

Not expressed parts (sequences) of the RNA

Exons

Expressed parts (sequences) of the RNA

In RNA, the 5’ end is called the…

the “5-prime cap” (of RNA)

In RNA, the 3’ is called the…

The “poly-A tail” (of RNA)

Alternative splicing makes…

[this] makes RNA Isoforms. Only splices the exons & ignores introns. Makes forms of mRNA

Codon

Codons are sequences (three nucleotides) on mRNA that specify particular amino acids during protein synthesis.

Each codon relates to one specific amino acid or serves as a start/stop signal.

AUG is this codon

The Start Codon

What are the three sites in the ribosomal subunit?

The E site, P site, and A site.

Transcription initiation complex

Activator proteins

Enhancer regions

Promoter regions

Transcription factors

Binds to promoter region (before the gene)

Retrovirus’ unique trait (differentiates from viruses)

Reverse transcribes DNA from RNA

The 3 categories of mutations

Harmful, Beneficial, and Neutral