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 CYCLEAND 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 MITOSIS

• NUCLEUS CHROMOSOMES

• NUCLEOLUS• GRAINY

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 doublehelix

DNA andhistones

Chromatin SupercoiledDNA

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 DUPLICATEDCHROMOSOME; SISTER CHROMATIDSHELD TOGETHER AT:CENTROMERE ENDS OF DNAMADE OF REPEATINGUNITS CALLED:TELOMERES