CHROMOSOMES & DNA REPLICATION

2014

DNA

WHERE IS DNA FOUND IN THE CELL?

IN PROKARYOTIC CELLS, DNA IS LOCATED IN THE CYTOPLASM.

MOST PROKARYOTES HAVE A SINGLE, CIRCULAR DNA MOLECULE THAT CONTAINS THE CELL’S GENETIC INFORMATION.

THIS SINGLE DNA MOLECULE IS THE CELL’S CHROMOSOME

Bacterial Chromosome

WHERE IS DNA FOUND IN THE CELL?

IN EURKARYOTIC CELLS, DNA IS FOUND IN THE NUCLEUS IN THE FORM OF CHROMOSOMES.

EUKARYOTIC CHROMOSOMES CONTAIN BOTH DNA AND PROTEIN TIGHTLY PACKED TOGETHER TO FORM CHROMATIN.

CHROMATIN

CONSISTS OF HISTONES WHICH IS DNA TIGHTLY COILED AROUND PROTEINS.

TOGETHER, THE DNA AND HISTONE MOLECULES FORM A BEADLIKE STRUCTURE CALLED A NUCLEOSOME.

FUNCTIONS OF NUCLEOSOMES

1. HELP SEPARATE CHROMOSOMES DURING MITOSIS.

2. HELP FOLD ENORMOUS LENGTHS OF DNA INTO THE CELL NUCLEUS

3. HELP REGULATE HOW GENES ARE “READ” TO MAKE PROTEINS

DNA – THE HEREDITARY MATERIAL

DNA IS A DOUBLE HELIX – TWO STRANDS WOUND AROUND EACH OTHER.

THE TWO STRANDS (BACKBONE) ARE MADE OF PHOSPHATE AND DEOXYRIBOSE SUGAR.

THE TWO STRANDS ARE CONNECTED BY THE NITROGEN BASES.

THE BASES ARE CONNECTED BY HYDROGEN BONDS.

HYDROGEN BONDS

ARE THE CHEMICAL BONDS THAT HOLD THE NITROGEN BASES TOGETHER;

ARE NOT AS STRONG AS COVALENT OR IONIC BONDS;

ARE EASILY BROKEN AND REFORMED BETWEEN THE NITROGEN BASES

DNA STRUCTURE

REPEATING UNITS CALLED NUCLEOTIDES

DNA NUCLEOTIDE COMPONENTS: 5-CARBON SUGAR – DEOXYRIBOSE PHOSPHATE GROUP NITROGENOUS BASE (BASE THAT

CONTAINS NITROGEN)

DNA NUCLEOTIDE

DNA’S NITROGEN BASES

THERE ARE 4 NITROGEN BASES IN DNA:1. ADENINE2. THYMINE3. CYTOSINE4. GUANINE

Nitrogen Bases

ADENINE & GUANINE ARE CLASSIFIED AS PURINES – 2 RINGS IN THEIR STRUCTURE

CYTOSINE AND THYMINE ARE CLASSIFIED AS PYRIMIDINES- WHICH HAVE ONE RING IN THEIR STRUCTURE

CHARGAFF’S RULES

THE PERCENTAGE OF ADENINE AND THYMINE ARE ALMOST EQUAL IN ANY DNA SAMPLE

THE PERCENTAGE OF CYTOSINE AND GUANINE ARE ALMOST EQUAL IN ANY DNA SAMPLE

NITROGEN BASES

BASE PAIRING RULE: THESE 4 BASES ALWAYS PAIR THE

SAME WAY IN DNA. ADENINE PAIRS WITH THYMINE GUANINE PAIRS WITH CYTOSINE

WHAT IS THE NUCLEOTIDE SEQUENCE?

A - _____ T - _____ C - _____ T - _____ A - _____ G - _____

WHAT IS THE NUCLEOTIDE SEQUENCE?

C ______ G ______ A ______ T ______ C ______ C ______

DNA

THE NUCLEOTIDES CAN BE JOINED TOGETHER IN ANY ORDER MEANING THAT ANY BASE SEQUENCE IS POSSIBLE

HOW DNA REPLICATION OCCURS

CARRIED OUT BY A GROUP OF ENZYMES ENZYME – A PROTEIN THAT ACTS AS A

BIOLOGICAL CATALYST; CATALYST – SUBSTANCE THAT SPEEDS UP THE

RATE OF A CHEMICAL REACTION CATALYSTS WORK BY LOWERING A

REACTION’S ACTIVATION ENERGY

DNA REPLICATION

HELICASE UNWINDS THE DNA STRAND EACH STRAND OF DNA SERVES AS A

TEMPLATE FOR THE NEW STRAND THAT IS BEING MADE

DNA POLYMERASE I READS EACH DNA BASE, ADDING COMPLEMENTARY BASES TO THE NEW STRAND

DNA REPLICATION

DNA POLYMERASE III MAKES THE NEW STRANDS LONGER AS DNA POLYMERASE I ADDS NEW BASES

REPLICATION CONTINUES UNTIL A STOP CODE IS REACHED

LIGASE THEN JOINS THE DNA STRANDS BACK TOGETHER AND INTO A DOUBLE HELIX

DNA REPLICATION

WHEN REPLICATION IS COMPLETE, THE NEW DNA MOLECULE IS MADE OF ONE ORIGINAL DNA STRAND AND ONE NEW DNA STRAND.