interactive notes pgs. 295-299 12-2 chromosomes & dna replication
DESCRIPTION
CHROMOSOME STRUCTURE The nucleus of a human cell must fit more than 1 meter of DNA! Chromatin = DNA + Protein packed together Chromatin is coiled around proteins, called histonesTRANSCRIPT
I N T E RAC T I V E N O T E S P G S . 2 9 5 - 2 9 9
12-2 CHROMOSOMES & DNA REPLICATION
LOOKING BACK…• Prokaryotes• DNA in the
cytoplasm• Single large DNA
molecule, called a chromosome
• Eukaryotes• 1000x amount of
DNA as prokaryotes• Many
chromosomes in the nucleus
CHROMOSOME STRUCTURE
• The nucleus of a human cell must fit more than 1 meter of DNA!• Chromatin = DNA
+ Protein packed together• Chromatin is coiled
around proteins, called histones
EUKARYOTIC CHROMOSOME STRUCTURE
DNA REPLICATION
• Replication is the copying process to duplicate DNA (before cell division)• DNA strands are complementary to each
other• Replication fork = where separation and
replication occur• The DNA molecule separates and the
original strand serves as a template or parent strand• Two new complementary (daughter) strands are
formed
Example: If the template strand has the sequence
TACGTTWhat would be the sequence of the complementary DNA strand that forms during replication?
Remember: Adenine (A) pairs with thymine (T)Guanine (G) pairs with cytosine (C)
Answer: ATGCAA
MECHANISM OF DNA REPLICATION
• Many enzymes are involved in DNA replication• DNA Helicase: Unzips the DNA strands • Key Enzyme: DNA POLYMERASE• Adds new nucleotides • Proofreads each new
DNA strand
OTHER IMPORTANT PROTEINS
• SSB or Single-Stranded binding protein• Binds to single strand DNA and prevents it from
reforming a double helix• DNA Primase• Synthesizes short RNA primers• Becomes a target for new DNA synthesis
• DNA ligase• Binds all of the new strand pieces together
THREE STEPS IN DNA REPLICATION
• Unwinding• DNA Helicase unwinds and separates the parent strands
• Complimentary Base Pairing• DNA is synthesized in the 5’ to 3’ direction• Leading strand: synthesis is easier (it is in 5’ to 3’ direction for
new strand)• Lagging strand: not oriented in 5’ to 3’ direction
• Creates Okazaki fragments joined by DNA ligase• Joining• DNA polymerase binds short RNA sequences together• Results in two identical Semi-conservative double helix
molecules• One old strand and one new strand
REPLICATION IN ACTION…
• https://www.youtube.com/watch?v=zdDkiRw1PdU
Copyright Pearson Prentice Hall
Nitrogen Bases
Replication Fork
DNA Polymerase
Replication Fork
Original strandNew Strand
GrowthGrowth