Download How many chromosomes?

Lesson 14a:
DNA Structure and Replication
Trans – carry
Scrib – write
Co – together
soma - body
gen - origin
re - 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?
DNA Folding (Best) 2:14
http://www.cells.de/cellseng/1medienarchi
v/Zellstruktur/Zellkern/DNA_condensation/
Flash__C13105.htm
DNA folding
http://www.dnatube.com/video/47/3Dstructure-of-chromosome
DNA folding
http://www.labaction.com/view_video.ph
p?viewkey=f0af142b6d3bead98a92
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
DNA
cell
nucleus
 But the DNA starts
loosely wound in the
nucleus
 If you tried to divide it
like that, it could tangle
& break
Organizing & packaging DNA
DNA
cell
nucleus
DNA has been
“wound up”
DNA in chromosomes in
everyday “working” cell
cell
nucleus
DNA in chromosomes in cell
getting ready to divide
Now, how many chromosomes do you see?
Is this a male or female?
KARYOTYPE = display of chromosomes laid out in pairs from largest
How many
chromosomes
do you
see?
to smallest.
Sex cells
are always placed
at the
end.
How many chromosomes?
Which gender (sex)?
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
DNA Replication
• 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
• Enzyme
– DNA polymerase
– adds new bases
DNA
polymerase
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
• 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
Copying DNA
Coil DNA into
compact chromosomes
double-stranded
human chromosomes
ready for mitosis
Make sure you do everything in
your power to plan your
schedule wisely
the day before
the test.
TEST
TIPS
Plan to
get to bed
early so you will
be well rested for the
day of the test.