AP Bio Unit 5: Cell Communication & Cell Cycle

DNA Function

Stores genetic info & is the blueprint for building proteins

DNA Structure

• Double-stranded helix (2 sugar phosphate backbones)

• Nucleic acids (polymer) are made up of nucleotide monomers

• Nucleotides have three parts:

  • Phosphate Groups (- charged)

  • Deoxyribose (5-carbon sugars)

  • Nitrogen Bases

    • Adenine

    • Thymine

    • Guanine

    • Cytosine

RNA Structure

• Single-stranded (1 sugar phosphate backbone)

• Ribose Sugar

• Nitrogen Bases:

  • Adenine

  • Uracil

  • Cytosine

  • Guanine

Nucleotides are connected by a ______ bond between the sugar of one and the phosphate group of the other

Phosphodiester

In DNA, the complementary nitrogen bases are connected via ______ bonds.

Hydrogen

Nucleotides are attached together through ______ ______.

Dehydration Synthesis

Pyrimidines

Nitrogen bases that are single ringed - C, T, U

Purines

Nitrogen bases that are double ringed - A, G

Pairing of Nucleotides

• Pyrimidines always bond with purines

• A & T = 2 Hydrogen Bonds

• G & C = 3 Hydrogen Bonds

Deoxyribose has __ Carbon atoms, which are numbered clockwise.

5

DNA Directionality

DNA is antiparallel because complementary strands run in opposite directions (5’ → 3’ & 3’ → 5’)

DNA Synthesis

Occurs in the S phase of the cell cycle, when the DNA is in chromatin form

1. Cell reproduction (mitosis)

2. Gamete production (meiosis)

Semiconservative Process (in DNA synthesis)

The two DNA strands are complementary, which means base pairing allows each strand to serve as a template for a new strand

Helicase in DNA Replication

Unwinds part of the DNA double helix

Topoisomerase in DNA Replication

Helps relieve the strain of unwinding by breaking, swiveling, and rejoining DNA strands

DNA Polymerases in DNA Replication

Connects nucleotides together to make a strand

RNA Polymerase (a.k.a Primase, DNA Primase, etc) in DNA Replication

Adds a few nucleotides of RNA (RNA primer) to get the process started

Ligase in DNA Replication

Connects DNA fragments together

DNA Synthesis: Step 1

DNA Helicase unwinds the DNA strands. Topoisomerase relaxes supercoiling in front of the replication fork.

DNA Synthesis: Step 2

Complementary nucleotides are matched with the ones of the original DNA parent strand to create a new strand:

1. RNA polymerase (primase) adds a few nucleotides so DNA polymerase can get started; the RNA nucleotides are later replaced

2. DNA polymerase connects the nucleotides but can only add nucleotides to the 3’ end of a nucleotide

Leading Strand

Once an RNA primer is added, DNA polymerase can continuously add nucleotides in the 5’ to 3’ direction - the DNA strand is copied in a continuous way

Lagging Strand

Made in Okazaki fragments that are later joined together by ligase - the DNA strand is copied discontinuously

→ RNA primers are later removed and replaced by DNA nucleotides

Telomeres

The ends of chromosomes in eukaryotes have repeating, non-coding sequences called telomeres that serve as protective caps

→ Loss of bases at 5′ ends in every replication: Chromosomes get shorter with each replication (limits # of cell divisions to about 50) → aging process

Telomerase

Can add DNA bases at 5’ end; high activity in stem cells and cancers but not in most somatic cells