DNA: THE MOLECULE OF LIFE

DNA REPLICATION (SEMI-CONSERVATIVE REPLICATION)1. DNA uncoils

2. Helicase enzyme unzips DNA - weak hydrogen bonds that hold complementary nitrogen bases together break.

3. The two strands move apart and each acts as a template or pattern.

4. Replication occurs in both directions.

5. DNA-polymerase brings in complementary nucleotides and joins them to their complementary bases

◦ A T◦ G C

DNA polymerase reads the base pairing in the 3’ to 5’ direction.

Short nitrogen base sequences called OKazaki fragments follow behind the polymerase and add nucleotides in the 5’ to 3’ direction.

When the Okazaki fragments meet the already made new strand, a DNA ligase enzyme seals the pieces together

Many DNA polymerase are working at the same time at different points along the DNA molecule

DNA polymerase also proof reads the mistakes and repairs

DNA REPLICATION

• Each resulting DNA molecule has one old and one new strand.

◦ This is semi - conservative replication because only the parent strands are conserved.

◦ The original, integrated molecule is not conserved.

Source: Access Excellence @ the National Health Museumhttp://www.accessexcellence.org/RC/VL/GG/possible.php

DNA REPLICATION

parent strand

daughter strand

Source: Mariana Ruiz

DNA REPLICATION

Source: ©1999 William Reusch, All rights reserved (most recent revision 7/16/2007) – Permission granted

Let’s watch this in action!http://www.dnalc.org/resources/

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TRANSCRIPTION Purpose of replication:

◦ to make a single strand complementary template

Source: ©1999 William Reusch, All rights reserved (most recent revision 7/16/2007) – Permission granted

TRANSCRIPTION

1. As in replication, the chromosome (DNA)

uncoils, splits down the centre and the two

halves move apart.

2. Using RNA nucleotides, a strand of mRNA is

constructed using the DNA as a pattern

(mRNA is single stranded and thymine is

replaced by uracil).

TRANSCRIPTION

3. The strand of mRNA breaks away from the

DNA and travels out of the nucleus into the

cytoplasm to be used for protein synthesis.

4. The DNA strands come back together and coil

up again.

Source: ©1999 William Reusch, All rights reserved (most recent revision 7/16/2007) – Permission granted

TRANSCRIPTIONRNA polymerase joins RNA nucleotides together making mRNA

mRNA molecules carries a series of codons (sequence of 3 nitrogen bases) that will be used to order the sequence of amino acids in a protein

Once the single strand of mRNA has DNA’s complementary bases (in sets of codons or 3 base pairs) it leaves the nucleus and travels to ribosomes in the cytoplasm where translation or protein synthesis can occur.

Source: Access Excellence @ the National Health Museumhttp://www.accessexcellence.org/RC/VL/GG/mRNA.php

Let’s watch this in real time…http://www.dnalc.org/resources/

3d/index.html