ap biology week 4 - dna and cell division
DESCRIPTION
Weeks 4/5 of our AP cram course, on the topics of DNA, chromosomes, and mitosis.TRANSCRIPT
Cell Division and Genetics
7/9/2013AP Biology Week 5
Warm Up: Organelle Function
Name an organelle (or cell part): That is found only in plants That contains DNA That secretes proteins That modifies proteins That has a double membrane That helps the cell move That is found in prokaryotic cells That contains acids and enzymes
DNA Structure
Recall that DNA is a polymer consisting of many repeating monomers. Each monomer in DNA is a nucleotide.
The nucleotide has threeparts: Sugar (deoxyribose) Phosphate group Nucleotide base (adenine,
thymine, guanine, or cytosine)
DNA Base Pairs
Every nucleotide base “pairs” with a different specific base: adenine pairs with thymine, guanine with cytosine They attach with hydrogen
bonds like a zipper. The sugar-phosphate
background causes the zipper to curl or spiral into a double helix shape.
The “Code” of DNA
DNA’s double helix keeps a double copy of its information, one copy on each side of helix, coded in opposite base pairs. This comes in handy for replication.
Note that you only need one strand of DNA to recreate the other half. Try here:
DNA Replication
When DNA copies itself, it pulls apart its two template strands to form complementary strands.
First, DNA unzips the helix with the enzyme helicase
Next, the enzyme DNA polymerase does the base-pair matching
And finally, the enzyme DNA ligase binds the strands back together.
DNA Replication
Because deoxyribose sugars are pentagons, they are asymmetrical, with a 5’ and 3’ end.
Enzymes (polymerase, ligase) move smoothly in the 5’3’ direction, called the leading strand
The lagging strand in the 3’5’ direction must be synthesized in pieces, called “Okazaki fragments” and then tied together later with ligase.
AP Questions on DNA
1. What would be the sequence of bases of the complementary DNA strand to the template below? (1990:40)
GTAGTAGGTa) GTAGTAGGTb) CAUCAUCCAc) AUGAUGAAUd) UCGUCGUUCe) CATCATCCA
AP Questions on DNA
2. DNA replication can be best be described as semiconservative because:
a) The nucleotide bases are conserved to use over and over again in different molecules.
b) DNA is the common genetic code that is conserved between all living organisms
c) DNA replicates by unzipping, replicating complementary strands, and rezipping the templates to conserve for later.
d) Each new DNA strand conserves one template strand and one new complementary strand.
AP Questions on DNA
3. Describe in 2-3 sentences what is meant by the “five prime” and “three prime” end of a DNA strand, explaining how this affects the DNA replication process.
Chromosomes and Nuclear Stuff DNA in the nucleus is
tightly coiled around histone proteins, forming a stringy substance called chromatin.
During reproduction, the strings coil up even more to form chromosomes. Chromosomes are made up of
two chromatids which are precise copies of each other
The chromatids are connected at the centromere
The Life of a Cell
During interphase, the cell grows, develops, copies its DNA, and does normal cell stuff.
During mitosis, the cell divides into two “daughter” cells. The daughter cells are
clones of the mother cell because they haveidentical DNA
The lengths of these two stages depends onthe type of cell involved
Interphase: G1, S, G2
G1 – “first gap” phase Cell grows and makes proteins DNA is uncoiled in loose chromatin Restriction point: checkpoint before
continuing G0 phase – dormant cells get the signal to
pause S – “synthesis” phase
Cell copies (synthesizes) its DNA, doubling it G2 – “second gap” phase
Cell continues growth, doubling its organelles to prepare for division
Mitosis – Asexual Cell Division
Prophase – “P” for “prepare” Chromosomes condense in the
nucleus Nuclear membrane dissolves Spindle apparatus forms
Metaphase – “M” for “middle” Chromosomes align at
metaphase plate (the middle of the cell)
Spindle fibers attach to centromeres.
Mitosis – Asexual Cell Division
Anaphase – “A” for “apart” Chromosomes pull apart,
breaking centromeres Sister chromatids pull to
opposite poles of the cell Spindle fibers contract
Telophase – “T” for “twin” Nuclear membranes re-form Chromosomes disentangle
into chromatin Cytokinesis, division of the
cytoplasm
The Cell Cycle and Cancer
The cell cycle (interphase and division) is highly regulated, occurring at different paces. Fast cell division: stomach
cells, hair, skin, blood Slow cell division: liver, brain
(no division) Restriction points, especially
at the end of G1, let your body signal to a cell whether to halt Disorders of the cell cycle can
cause cancer—uncontrolled cellular reproduction
Meiosis
Skip to “ploidies” presentation for details.