2006-2007 Regents Biology

Biology is the only subject in which multiplication is the same thing as division…

2006-2007 Regents Biology

Making New CellsMaking New DNA

Regents Biology

Where it all began…

You started as a cell smaller than a period at the end of a sentence…

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Going from egg to baby…. the original fertilized egg has to divide…

and divide…and divide…

and divide…

Getting from there to here…

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Why do cells divide… for reproduction

one celled organisms (clones)

for growth & development from fertilized egg to multi-celled organism

for repair replace cells that die from

normal wear & tear or from injury

amoeba

starfish

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Dividing cells… What has to be copied

DNA organelles cell membrane lots of other

molecules enzymes

animal cellplant cell

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Copying DNA A dividing cell duplicates its DNA

creates 2 copies of all DNA separates the 2 copies to opposite ends

of the cell splits into 2 daughter cells

But the DNA starts loosely wound in the nucleus

If you tried to divide it like that, it could tangle & breaknucleus

cell

DNA

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Organizing & packaging DNA

nucleus

cell

DNA

nucleus

cell

4 chromosomesin this organism

DNA in chromosomes ineveryday “working” cell

DNA in chromosomes in cell getting ready to divide

DNA has been “wound up”

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Chromosomes of Human Female

46 chromosomes23 pairs

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Chromosomes of Human Male

46 chromosomes23 pairs

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Paired bases DNA structure

double helix 2 sides like a ladder

Bases match together A pairs with T

A : T C pairs with G

C : G

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Watson and Crick

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Copying DNA Matching bases allows

DNA to be easily copied

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Making new DNA Copying DNA

replicationDNA starts as a double-stranded

molecule matching bases (A:T, C:G)

then it unzips…

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DNA replication Strands “unzip” at the weak bonds

between bases

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DNA replication

DNA polymerase

Enzyme DNA polymerase adds new bases

DNA basesin nucleus

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DNAPolymerase

Copying DNA Build daughter DNA strand

use original parent strand as “template”

add new matching bases synthesis enzyme =

DNA polymerase

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New copies of DNA Get 2 exact copies of DNA to split

between new cells

DNA polymerase

DNA polymerase

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Copied & Paired Up Chromosomes

centromere

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Copying & packaging DNA

Copying DNA

Coil DNA into compact chromosomes

When cell is ready to divide… copy DNA first, then… coil up doubled chromosomes

like thread on a spool… now can move DNA around cell without having

it tangle & break

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double-strandedhuman chromosomesready for mitosis

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DNA must be duplicated…

nucleus

cell

DNA in chromosomes

nucleus

cell

duplicated chromosomes

chromosomes in cell

4 single-stranded chromosomes

duplicatedchromosomes

4 double-stranded chromosomes

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Mitosis: Dividing DNA & cells Stage 1: cell copies DNA

nucleus

cell

DNA Copy DNA!

(interphase)

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Mitosis: Dividing DNA & cells Stage 2: DNA winds into chromosomes

DNA is wound up into chromosomes to keep it organized

nucleus

cell

duplicated chromosomes Wind up!

(prophase)

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Mitosis: Dividing DNA & cells Stage 3: Chromosomes line up

chromosomes line up in middle attached to protein “cables” that will

help them move

duplicated chromosomeslined up in middle of cell

Line up!

(metaphase)

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Mitosis: Dividing DNA & cells Stage 4: Chromosomes separate

chromosomes split, separating pairs start moving to opposite ends

chromosomes split & move to opposite ends

Separate!

(anaphase)

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Mitosis: Dividing DNA & cells Stage 5: Cell starts to divide

cells start to divide nucleus forms again

Divide!

(telophase)

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Mitosis: Dividing DNA & cells Stage 6: DNA unwinds again

cells separate now they can do their every day jobs

Bye Bye!

(cytokinesis)

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New “daughter” cells Get 2 exact copies of original cells

same DNA “clones”

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Cell division in Animals

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Mitosis in whitefish embryo

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Mitosis in plant cell

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onion root tip

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Overview of mitosis

Copy DNA Wind Up

Line Up Separate Divide

Bye-Bye!

2006-2007 Regents Biology

Any Questions??

Any Questions??