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.