Transcript cell cycle notes 1

Cell Growth Review
• Size limitations—most cells are small, but
size varies
– Red Blood Cells less than 1mm diameter
– Nerve cells up to a meter or more in length
• Need to be small enough for diffusion to
occur efficiently
– Wastes out
– Nutrients in
THE CELL CYCLE
AND DNA STRUCTURE
KEY CONCEPT:
CELLS HAVE DISTINCT PHASES
OF GROWTH, REPRODUCTION,
AND NORMAL FUNCTIONS
Cell Cycle
• Cell grows, prepares for division, and
divides to form two new genetically
identical daughter cells.
• Form of asexual reproduction
• Needed for growth and development,
wound healing
• Cells have different life spans
– Hours to NEVER (for humans)
– Minutes (bacteria)
Stages of Cell Cycle
• Interphase
– Longest
• G1 phase
• S phase
• G2 phase
• Cell Division
– Shortest
• M phase
CELL CYCLE STAGES
• GAP 1 ( G1 )
–CELLS GROW
–CARRY OUT NORMAL FUNCTIONS
–REPLICATE THEIR ORGANELLES
–LONGEST PART OF CELL CYCLE
CELL CYCLE STAGES
• SYNTHESIS ( S )
–DNA IN NUCLEUS COPIED
• DNA REPLICATION/DUPLICATION
–TWO COMPLETE SETS OF DNA
–Each chromosome consists of two
identical “sister” chromatids
attached at a centromere
CELL CYCLE STAGES
• GAP 2 ( G2 )
–CONTINUE NORMAL FUNCTIONS
–ADDITIONAL GROWTH
–CHECK POINT
• CELL SIZE
• UNDAMAGED DNA
• READY FOR MITOSIS & DIVISION
CELL CYCLE STAGES
• MITOSIS ( M )
– TWO PROCESSES:
• MITOSIS – DIVISION OF CELL
NUCLEUS AND ITS CONTENTS
–NUCLEAR MEMBRANE DISSOLVES
–DUPLICATED DNA CONDENSES
–THEN SEPARATES INTO 2 NUCLEI
• CYTOKINESIS – DIVISION OF THE
CELL CYTOPLASM RESULTING IN
2 DAUGHTER CELLS
What would happen if…
• The cell divided without replicating its DNA
first?
• The cell continued through the cell cycle
without growing?
• The cell kept growing without dividing?
• Kept replicating its DNA without dividing?
CELL CYCLE STAGES
• MITOSIS
• CYTOKINESIS
INTERPHASE
• NUCLEUS
• NUCLEOLUS
• GRAINY
MITOSIS
CHROMOSOMES
CELLS DIVIDE AT
DIFFERENT RATES
•
•
•
•
PROKARYOTES FASTER THAN EUKARYOTES
IN HUMANS – S, G2, M : ABOUT 12 HOURS
G1 DIFFERS MOST AMONG CELL TYPES
RATE VARIES WITH : AGE, TYPE OF TISSUE ,
WEAR AND TEAR
• LIFE SPAN : FEW DAYS TO MANY YEARS
• G0 – CELLS UNLIKEY TO DIVIDE - NEURONS
Infer Do you think a skin cell would have a long
or short G1 stage? Explain why.
CHROMOSOME STRUCTURE
• CHROMOSOME: A LONG CONTINUOUS
THREAD OF DNA WITH MANY GENES
• HUMAN BODY CELLS CONTAIN 46 EACH
• DNA IN ONE CELL ABOUT 3 METERS (10’)
• WRAPS AROUND HISTONE PROTEINS
– LIKE THREAD ON SPOOLS, AT REGULAR
INTERVALS; SIMILAR TO BEADS ON A STRING
CHROMATIN: LOOSE COMBINATION OF
DNA AND PROTEINS
FIGURE 5.5
• CHROMOSOME STRUCTURE
DNA double
helix
DNA and
histones
Chromatin
Supercoiled
DNA
CHROMOSOME STRUCTURE
• DURING MITOSIS OF CELL DIVISION,
CHROMATIN CONDENSES AROUND
ORGANIZING PROTEINS
• FORMS SMALL
THICK RODS
• LOOK LIKE “X”
• DNA COPIED
IN S STAGE
• DNA loose and
hard to see in
interphase
CHROMOSOME STRUCTURE
• CHROMATID: ONE HALF
OF A DUPLICATED
CHROMOSOME;
SISTER CHROMATIDS
HELD TOGETHER AT:
CENTROMERE
ENDS OF DNA
MADE OF REPEATING
UNITS CALLED:
TELOMERES