Cell Division 2: DNA Replication

1. CELL DIVISION 2:
DNA Replication
ppt. by Robin D. Seamon

2. N U C L E I C A C I D S
• Made of nucleotides
• Make up macromolecules of DNA
1. DNA Replication (makes copies of itself)
2. Encodes information (for proteins to be made)
3. Controls & instructs cells
4. Mutations (molecule of heredity)
2

3. D N A
Deoxyribonucleic Acid
double helix
structure containing
genetic information
SIZE: (in each cell)
3 billion base pairs
6 feet long
10 trillion cells in
body!!

4. Prokaryotes- DNA is in the cytoplasm; during
binary fission, DNA forms round structure called
plasmids
Eukaryotes- DNA is inside the nucleus; double-
helix structure

5. VOCABULARY
• chromosomes- threadlike structure of nucleic
acids containing genetic information in the
form of genes
• genes- unit of heredity transferred from
parent to offspring; a distinct sequence of
nucleotides
• nucleotides- A, T, C, G

6. DNA Strands per human cell:
• 23 base pairs of chromosomes
A – T C – G
• each chromosome has 2 strands of DNA
(double helix)
• 42 X 6 = 92 strands of DNA in each body cell

7. • DNA is in all living things
• fundamental language of all of life (all life
forms can read it)
• Plants, animals, bacteria, protists, fungi, some
viruses
• these coded instructions are read (translated)
by ribosomes and then used to build proteins
(transcripted) for the body

8. COMMON LANGUAGE OF LIFE

9. genome: complete set and pattern of genes
present in a cell; each species has its own
pattern/genome
example:
HUMANS
• 99.9 % genes identical to every one else
• 0.1% makes us unique

10. • Every cell in a living organism’s body (except red
blood cells) have a copy of their species genome
written in the code.
• Different genes (pieces of DNA) are turned on or
off where they are needed
10

12. **DNA (chemical basis of heredity) is in genes
**Genes are ON chromosomes
Chromosomes (made of two sister chromatids)
• A “packaged structure” made of DNA &
proteins
• single strand of tightly coiled DNA
• too thin to see without a microscope
• become short and fat & pairs up with a sister
chromatid to
make an
X shape during
mitosis

13. Chromatin: long, thin nuclear strands
Chromatid: after chromatin are copied, they are
called sister chromatids
Chromosome: the sister chromosomes combine
to make an x-shaped chromosome package
Chromosomes (made of two sister chromatids)
• single strand of tightly coiled DNA
• too thin to see without a microscope
• become short and fat & pairs up with a sister
chromatid to make an X shape during mitosis

14. C
CC
C C
P Nitrogen base
DNA Structure
nucleic acid- monomer
• sugar + phosphate + Nitrogenous base
• Groups of nucleic acids make strands of the
polymer DNA

15. C
CC
C C
P Nitrogen base

16. Nitrogen Bases:
PURINES
• Adenine (A) BIG
• Guanine (G) BIG
PYRIMIDINES
• Cytosine (C) (small)
• Thymine (T) (small)
C
CC
C C
P Nitrogen base
BASE

17. Nitrogen
base

18. Backbone:
sugar

19. Backbone:
phosphate

20. Base-pairing rule:
purines pair with pyrimidines and are held
together with hydrogen bonds
• sequence: order of bases
A pairs with T
C pairs with G
codon: 3 base pairs
A T T G C T C A T
T A A C G A G T A

21. Double helix - Twisted ladderDNA
Structure
PAIRS:
Number of A will
= number of T
Number of G will
= number of C

22. genes
• one gene makes one protein
• the gene is the instruction sequence for the
production of that protein
protein
• carries out a function
example:
hemoglobin carries
oxygen
GENE EXPRESSION:

24. Mutations: a change in the coding of a gene
-can occur through:
1. Deletion: cell accidentally omits a piece of the
DNA
2. Duplication: cell accidentally makes an extra
copy of the DNA piece
3. Insertion: cell accidentally adds a piece of
DNA
4. Translocation: cell accidentally puts a piece of
genetic sequence in the wrong place.
24

25. ACTIVITY
• THE OLD RED DOG WAS TOO BIG FOR HIS BED
• Deletion that would delete the D in OLD…
• THE OLR EDD OGW AST OOB IGF ORH ISB ED
• Inversion of the word DOG...
• THE OLD RED GOD WAS TOO BIG FOR HIS BED
25

26. mutation example:
• one mutation in the gene for hemoglobin
(change T to A) causes sickle cell anemia

27. DNA REPLICATION:
Detail

28. DNA REPLICATION
1. Helicase- enzyme unzips the double helix
2. Hydrogen bonds break
3. DNA polymerase- enzyme builds the new
DNA
• Selects the new nucleotide (matches it)
• Makes sure it is correct
• Forms a new bond

29. Enzyme
Substrate

30. Semi-conservative:
DNA replication makes 2 new DNA strands
with ½ the old strand and ½ the new strand

31. Two new
strands

32. The specific pairing of bases allows for an
EXACT copy of the DNA to be made.

33. Double helix = Twisted ladder