Lesson 14a: DNA Structure and Replication Trans – carrysoma - body Scrib – writegen - origin Co – togetherre - again

A single DNA molecule can be more than a meter long! So, how do you pack it into the nucleus of one tiny cell? A single DNA molecule can be more than a meter long! So, how do you pack it into the nucleus of one tiny cell? DNA folding structure-of-chromosome DNA folding p?viewkey=f0af142b6d3bead98a92 DNA Folding (Best) 2:14 v/Zellstruktur/Zellkern/DNA_condensation/ Flash__C13105.htm

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 & break nucleus cell DNA

Organizing & packaging DNA nucleus cell DNA nucleus cell DNA in chromosomes in everyday “working” cell DNA in chromosomes in cell getting ready to divide DNA has been “wound up”

How many chromosomes do you see? KARYOTYPE = display of chromosomes laid out in pairs from largest to smallest. Sex cells are always placed at the end. N o w, h o w m a n y c h r o m o s o m e s d o y o u s e e ? I s t h i s a m a l e o r f e m a l e ? I T ’ S A G I R L !

How many chromosomes? Which gender (sex)? It’s a BOY!

Paired bases DNA structure – double helix 2 sides with rungs in the middle - like a twisted ladder Bases match together – A pairs with T A : T – C pairs with G C : G

DNA Replication Matching bases allows DNA to be easily copied

Copying DNA – making exact copies – Replicate = to copy – DNA starts as a double-stranded molecule matching bases (A:T, C:G) – Bonds between A:T and C:G are weak DNA Replication

Strands “unzip” at the weak bonds between bases DNA Replication

DNA polymerase Enzyme – DNA polymerase – adds new bases Free floating DNA bases in nucleus

DNA Replication Get 2 exact copies of DNA to split between the two new cells. DNA polymerase DNA polymerase Coach L14

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

double-stranded human chromosomes ready for mitosis

TESTTIPS Make sure you do everything in your power to plan your schedule wisely the day before the test. Plan to get to bed early so you will be well rested for the day of the test.