cell growth review size limitations—most cells are small, but size varies –red blood cells less...
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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
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THE CELL CYCLEAND DNA STRUCTURE
KEY CONCEPT:CELLS HAVE DISTINCT PHASES OF GROWTH, REPRODUCTION, AND NORMAL FUNCTIONS
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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)
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Stages of Cell Cycle
• Interphase– Longest
• G1 phase• S phase• G2 phase
• Cell Division– Shortest
• M phase
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CELL CYCLE STAGES• GAP 1 ( G1 )
–CELLS GROW–CARRY OUT NORMAL FUNCTIONS–REPLICATE THEIR ORGANELLES–LONGEST PART OF CELL CYCLE
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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
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CELL CYCLE STAGES
• GAP 2 ( G2 )–CONTINUE NORMAL FUNCTIONS
–ADDITIONAL GROWTH
–CHECK POINT• CELL SIZE
• UNDAMAGED DNA
• READY FOR MITOSIS & DIVISION
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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
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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?
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CELL CYCLE STAGES
• MITOSIS
• CYTOKINESIS
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INTERPHASE MITOSIS
• NUCLEUS CHROMOSOMES
• NUCLEOLUS• GRAINY
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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.
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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
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FIGURE 5.5• CHROMOSOME STRUCTURE
DNA doublehelix
DNA andhistones
Chromatin SupercoiledDNA
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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
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CHROMOSOME STRUCTURE• CHROMATID: ONE HALF OF A DUPLICATEDCHROMOSOME; SISTER CHROMATIDSHELD TOGETHER AT:CENTROMERE ENDS OF DNAMADE OF REPEATINGUNITS CALLED:TELOMERES