Bio: 8.1-8.2 - DNA & Replication

How are DNA, genes, and chromosomes related?

How are DNA, genes, and chromosomes related?

DNA makes up our genes, which are found on chromosomes

DNA Function

stores the genetic info of an organism as a “code” of bases

Gene

A segment of DNA that contains the info to make a specific protein

How are proteins and phenotypes related?

proteins = phenotypes, so different genes → different order of bases → different proteins → different phenotypes

DNA Structure

made of repeating nucleotides which are made of

• 5 carbon sugar (deoxyribose)

• phosphate group

• nitrogenous bases (a small organic molecule w/ a core ring made of carbon and nitrogen)

Deoxyribose

5 carbon sugar:

• 1’ carbon = nitrogenous base attaches

• 3’ carbon = -OH group

• 5’ carbon = phosphate attaches

Nitrogenous Bases

Each nucleotide has a different one:

• Adenine

• Guanine

• Cytosine

• Thymine

Purines

2 rings of C & N, larger → A & G

Pyrimidines

1 ring of C & N → C & T

Complementary Base Pairing

chemical structures “complement” each other

• A w/ T → 2 Hydrogen bonds

• g w/ C → 3 Hydrogen bonds

a purine must pair w/ a pyrimidine - consistent width

Chargaff’s Rule

# of A = # of T (and same w/ G & C) - small difference result from mutations

Sides of DNA

2 strands of alternating sugar & phosphates connected via covalent bonds (strong)

Anti-Parellel

side-by-side, but running in opposite directions

Ends of DNA

5’ ends = a phosphate

3’ ends = sugar w/ a “free” -OH groups at the 3’ C atom

When does DNA Replication occur?

during interphase of the cell cycle - before mitosis

Semi-conservative

each replicated DNA is made of one “old” and one “new” strand, but identical in the genetic info they hold

DNA Replication Location

begins at specific origins of replication along the DNA

Helicase

• binds to an origin of replication - breaks H bonds between base pairs

• separates the 2 strands of DNA (like unzipping a zipper)

  → creates replication fork

Primase

• builds RNA Primers - small pieces of RNA (a molecule similar to DNA

• provides a starting point for DNA to be built - has a 3’ end, so more nucleotides can attach

DNA Polymerase Short Definition

adds nucleotides to build new strands of DNA

DNA Polymerase Process

• builds new DNA off the 3’ ends of the primers - “reads” the old template DNA

• adds complementary bases in the 5’ → 3’ direction to build new DNA

• new nucleotides add to the 3’ ends via dehydration synthesis (H + OH → H2O)

• eventually removed and replaced w/ DNA

Leading Strand

replicated continuously toward the fork

Lagging Strand

replicated in Okazaki fragments away from the fork - b/c original DNA molecules is antiparallel

Ligase

connects the gaps in the sugar-phosphate backbone by creating covalent bonds between sugars & phosphates