BIO 181 Module 3 Exam Review

Central Dogma

tells the organization of genetic and protein structures

DNA → transcription → mRNA → translation → working proteins in ribosomes

Pyrimidine bases

smaller molecules, single-ring

• Cytosine (C)

• Thymine (T)

• Uracil (U) found in RNA

Purine Bases

larger molecules, double-rings (pure as gold)

• Guanine (G)

• Adenine (A)

Hydrogen Bonds

connect bases; rungs of the ladder

Phosphodiester bonds

collect nucleotides; side rails of the ladder

Chargaff’s Rules

Adenine (A) = Thymine (T)

Guanine (G) = Cytosine (C)

5’

Phosphate end

3’

Sugar end

Antiparallel Strands

DNA strands run in opposite directions

One strand 5’ → 3’

Other strand 3’ → 5’

How many chromosomes do humans have?

46

Histone

folds and wraps around DNA to keep it organized

Chromatin

extra condensed of double-helices; wraps around histones; condenses into chromosomes

Which stage in the cell cycle is when DNA replication occurs?

Interphase

Semi-Conservative DNA Replication

After replication

• One old original strand is kept

• One new synthesized strand is built

DNA Replication Steps

1. DNA is unzipped & the replication fork is formed

2. RNA primer is formed

3. DNA Polymerase III builds new complementary strands

4. DNA Polymerase I replaces RNA primers

5. Ligase combines Okazaki fragments

Helicase

unwinds DNA by breaking hydrogen bonds

Replication Fork

when DNA opens up and a Y-shaped structure forms

Single-Strand Binding Proteins

bind to single strands and keep them apart (prevents re-zipping)

Origin of Replication

sequence of bases that initiate unwinding

• unzipping results in two template strands that will be “read” to form their complementary strands

RNA Primer

short sequence of RNA that eventually allows DNA Polymerase to bind; starting point for DNA synthesis

Primase

protein that lays the RNA primer down

Leading strand

first base unzipped is on 3’

Lagging strand

first base unzipped is on 5’

DNA Polymerase III

builds new DNA/complementary strands on leading and lagging strands

• reads 3’ to 5’

• builds (synthesizes) 5’ to 3’

On the leading strand

DNA polymerase binds the primers and adds complementary bases continuously

• continuous, smooth, easy

On the lagging strand

DNA polymerase binds the primers and adds complementary bases discontinuously

• discontinuous, built in pieces (many Okazaki fragments)

DNA Polymerase I

removes RNA primers and replaces them with deoxyribonucleotides (DNA)

Ligase

(“glue”) joins Okazaki fragments; combines the sugar-phosphate backbone of the Okazaki fragments; seals sugar-phosphate backbone

Exonuclease Activity

helps correct mistakes by extracting incorrect bases, however, some mistakes may still occur

• proofreading ability of DNA polymerases that removes incorrectly paired nucleotides from a newly synthesized DNA strand