DNA Replication: Copying the Code - Biology Notes, Schemes and Mind Maps of Biology

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DNA

REPLICATION

BIOLOGY

LEMON BAY HIGH SCHOOL

COPYING THE CODE

• Each STRAND of the double helix has all the INFORMATION needed to reconstruct the other HALF by the mechanism of BASE pairing.
• Because each STRAND can be used to make the other STRAND, the strands are said to be COMPLEMENTARY.

THE REPLICATION PROCESS

• The two strands of the double helix have SEPARATED, or “UNZIPPED,” allowing two replication FORKS to form.
• As each new STRAND forms, new BASES are added following the rules of base PAIRING.
• A strand that has the sequence TACGTT produces a strand with the COMPLEMENTARY base sequence of ATGCAA.
• The result is TWO DNA molecules IDENTICAL to each other and to the ORIGINAL molecule.

THE ROLE OF ENZYMES

• DNA replication is carried out by a series of ENZYMES.
• These ENZYMES first UNZIP a molecule of DNA by breaking the HYDROGEN bonds between the BASE pairs and UNWINDING the two strands of the molecule.
• Each strand then serves as a TEMPLATE for the attachment of COMPLEMENTARY bases.
• Enzymes are PROTEINS with highly specific FUNCTIONS.

TELOMERES

• DNA at the TIPS of CHROMOSOMES are known as TELOMERES
• The DNA is particularly DIFFICULT to REPLICATE

PROKARYOTIC DNA REPLICATION

• In most PROKARYOTES, DNA replication does not start until regulatory PROTEINS bind to a single starting point on the CHROMOSOME. These proteins then trigger the beginning of the S phase, and DNA REPLICATION begins.
• Replication in most PROKARYOTIC cells starts from the SINGLE point and proceeds in TWO directions until the entire CHROMOSOME is COPIED.

EUKARYOTIC DNA REPLICATION

• Eukaryotic CHROMOSOMES are generally much BIGGER than those of prokaryotes.
• In eukaryotic cells, REPLICATION may begin at dozens or evens HUNDREDS of places on the DNA MOLECULE, proceeding in BOTH directions until each CHROMOSOMES is copied completely.

EUKARYOTIC DNA REPLICATION

• The two copies of DNA produced by REPLICATION in each chromosome remain closely associated until the cell enters PROPHASE of MITOSIS.
• At that point, the chromosomes CONDENSE and the two chromatids in each chromosome become clearly VISIBLE.
• They SEPARATE from each other in ANAPHASE of mitosis.