human biology introduction to the cell cycle & dna maui papaya truck
TRANSCRIPT
Cells reproduce by dividing in two. This is why we alternatively use the term “cell division.”
Cell reproduction is a defining feature of life.
Mechanisms of cell reproduction are the same for all eukaryotes although some variations occur due to specialization of the 200 types of specialized cells in humans.
Many familiar cell structures and regulation necessary
2.4 million new erythrocytes are produced per second!
Energy! Materials!
Cell Reproduction
Figure 17.1
Mitosis Nucleus divides
CytokinesisCell divides
Cell prepares for division.Growth continuesslowly.
Primary period of cell growth.
G2G1
S
DNA is duplicated.Growth continuesslowly.
M
G0
The Cell Cycle Creates New Cells Step by Step
• InterphaseLong growth period between cell divisions
• G1 (gap 1)– primary growth phase, very active growth
• S (synthesis)– synthesis of DNA for next cell division
• G2 (gap 2) final growth phase before cell division
• Mitotic phase (cell division phase)Mitosis
• Nuclear division– duplicated DNA is distributed between two daughter nuclei, nucleus
dividesCytokinesis– Cytoplasm divides, two new daughter cells are formed
DNA, Genes & Chromosomes
DNA replication • Process of copying DNA prior to cell division
Gene • Short segment of DNA that contains the code, or recipe, for a protein
or for enzymatic RNA• Smallest functional unit of DNA
Chromatin• Threadlike combination of DNA and histone proteins present in
interphase cells (preparing for division) or in resting cells (taking a break from division)
Chromosome• Rod-like structure of highly coiled chromatin in cells in the mitotic
phase of cell division
Double-stranded DNA
Histones
Chromatinmaterial:not visibleduringInterphase
One chromatid
Its sisterchromatidCentromere
Chromosome: visible during mitosis
DNA to Chromosome
Replication, Transcription & Translation: Overview
Transcription• Process of copying DNA information of a gene into mRNA
(messenger ribonucleic acid)• Occurs within the cell nucleus
Translation• Process of converting the mRNA code into one or more
proteins• Occurs in the cytoplasm at ribosomes
Figure 17.3
Replication
•Produces an exactcopy of DNA
•Occurs prior toevery cell division
Transcription
•Converts a portion ofdouble-stranded DNA to asingle-stranded mRNA
•Occurs within the nucleus
Translation
•Converts an mRNAcode into one ormore proteins
•Takes place in the cytoplasm
DNA
mRNA
Protein
Replication: Copying DNA Before Cell Division
1. DNA strands uncoil and “unzip”
2. Each single strand serves as a template for the creation of a new complementary strand
3. DNA nucleotides are positioned and linked by DNA polymerase
4. Precise base-pairing (A with T & C with G) assures that an exact copy is made (mistakes corrected?)
Keys:
= Cytosine
= Adenine
= Guanine
= Thymine
Parent strand New(daughter)strandsforming
Parent strand
The double-stranded DNA unwinds, and each single strand serves as a template for a new complementary strand.
Replicationbubble
Parent DNAmolecule
2 completedaughter DNAmolecules
Parent strands
Newcomplementarystrands
The unwinding and the formation of new strands occur simultaneously at many sites on the DNA molecule. The sites of replication expand outward until they join. For simplicity the two strands are shown as parallel in (b), but in actuality they form a helical shape.
Replication: Mutations
• Alterations or “mistakes” in the DNA code
• Occur most frequently during DNA replication
• Causes: Chemical and physical forces
• Mutations can be:• Silent—have no effect• Deleterious—harmful, may result in cell death or cancer• Beneficial—basis for evolution
• Some mutations are repaired by repair enzymes
• The higher the rate of replication, the higher the mutation rate.