DNA Molecular basis of herdity

How much DNA is in my body?  DNA is found in every cell (except red blood cells)  Each cell contains roughly 2 meters of DNA containing ~3 BILLION base pairs  The human body has ~ 10,000,000,000,0000 cells  If you unraveled all the DNA from all of your cells and stretched it out end to end, it would stretch to the sun and back several times!  You could fit 25,000 strands of DNA side by side in the width of a human hair!

What is DNA? Importance of DNA DNA stands for deoxyribonucleic acid. It is one of two nucleic acids found in the cell.

What is DNA? Importance of DNA DNA is the blueprint for life. Every living thing uses DNA as a code for making proteins, which determines traits.

What is DNA? Importance of DNA For example, DNA contains the instructions for making the proteins (called pigments) which give your eyes color.

What is DNA? DNA is packaged into chromosomes. Each chromosome is composed of one continuous DNA molecule. The DNA molecule is wrapped around proteins and coiled tightly for protection

What is DNA? Remember, chromosomes are found in the nucleus of eukaryotic cells. Prokaryotic cells have a single chromosome free-floating in the cytoplasm.

Fill It In … DNA What? Where? Used for?

Discovery of DNA structure Many scientists worked to determine the source of heredity. Heredity is the passing of traits from parent to offspring. But how are those traits passed? Video

Discovery of DNA structure First, scientists determined that chromosomes controlled heredity and are made of DNA and proteins.

Discovery of DNA structure Then, scientists determined DNA was the chemical that controlled characteristics (traits of the organism) DNA Clearly Stated

Discovery of DNA structure Then, the race was on to reveal the structure of the DNA molecule

Discovery of DNA structure Rosalind Franklin was the first to take a clear “picture” of DNA using a technique called X-ray crystallography The “picture” offered a clue of the shape of DNA

Discovery of DNA structure Watson and Crick received credit for finalizing the model of DNA by using the picture taken by Franklin (given to them by Franklin’s research assistant - Maurice Wilkins), and by syntehsizing work completed by other scientists.

Structure of the DNA molecule DNA is a double helix. The double helix looks like a twisted ladder.

Structure of the DNA molecule The building blocks of DNA are called nucleotides. A nucleotide consists of three parts: A sugar (named deoxyribose) A phosphate group One of four nitrogen bases

Structure of the DNA molecule The four possible nitrogen bases in a DNA molecule are named: Adenine (A) Thymine (T) Guanine (G) Cytosine (C)

Fill It In … (From small to large) N _____ base + sugar + phosphate Two strands held together by _______ ______ D_______ H_________

Structure of the DNA molecule There are two strands of nucleotides in every DNA molecule held together by weak hydrogen bonds between the nitrogen bases.

Structure of the DNA molecule The nitrogen bases bond in a specific way. Adenine bonds with thymine (A-T). Guanine bonds with cytosine (G-C). This pattern is called complementary base pairing. DNA Structure and Function

Anti-parallel strands Nucleotides in DNA backbone are bonded from phosphate to sugar between 3 & 5 carbons DNA molecule has “direction” complementary strand runs in opposite direction 5 3 3 5

Copying DNA Replication of DNA base pairing allows each strand to serve as a template for a new strand new strand is 1/2 parent template & 1/2 new DNA

Fill It In … On this diagram: Highlight a nucleotide Then write out the NAME of the sugar beside one of the sugar molecules Finally, draw a box around the “backbone” and label.

Check Yourself! How is DNA connected to your traits? What larger structure is composed of DNA? What two parts of the nucleotide make up the sides (backbone) of a DNA molecule? What makes up one rung/”step” of the DNA “ladder”? What type of bond holds the rungs together?

Check Yourself! How is DNA connected to your traits? DNA CONTAINS THE INSTRUCTIONS FOR MAKING PROTEINS What larger structure is composed of DNA? What two parts of the nucleotide make up the sides (backbone) of a DNA molecule? What makes up one rung/”step” of the DNA “ladder”? What type of bond holds the rungs together?

Check Yourself! How is DNA connected to your traits? DNA CONTAINS THE INSTRUCTIONS FOR MAKING PROTEINS What larger structure is composed of DNA? CHROMOSOMES What two parts of the nucleotide make up the sides (backbone) of a DNA molecule? What makes up one rung/”step” of the DNA “ladder”? What type of bond holds the rungs together?

Check Yourself! How is DNA connected to your traits? DNA CONTAINS THE INSTRUCTIONS FOR MAKING PROTEINS What larger structure is composed of DNA? CHROMOSOMES What two parts of the nucleotide make up the sides (backbone) of a DNA molecule? SUGAR (DEOXYRIBOSE) AND PHOSPHATE GROUP What makes up one rung/”step” of the DNA “ladder”? What type of bond holds the rungs together?

Check Yourself! How is DNA connected to your traits? DNA CONTAINS THE INSTRUCTIONS FOR MAKING PROTEINS What larger structure is composed of DNA? CHROMOSOMES What two parts of the nucleotide make up the sides (backbone) of a DNA molecule? SUGAR (DEOXYRIBOSE) AND PHOSPHATE GROUP What makes up one rung/”step” of the DNA “ladder”? (COMPLEMENTARY) NITROGEN BASE PAIRS What type of bond holds the rungs together?

Check Yourself! How is DNA connected to your traits? DNA CONTAINS THE INSTRUCTIONS FOR MAKING PROTEINS What larger structure is composed of DNA? CHROMOSOMES What two parts of the nucleotide make up the sides (backbone) of a DNA molecule? SUGAR (DEOXYRIBOSE) AND PHOSPHATE GROUP What makes up one rung/”step” of the DNA “ladder”? (COMPLEMENTARY) NITROGEN BASE PAIRS What type of bond holds the rungs together? HYDROGEN BOND

Structure of the DNA molecule

Do all my cells have the same DNA? DNA replication copies DNA for new cells What is DNA?

DNA replication DNA is needed in each cell to make necessary proteins. Because DNA is so important, when a cell divides, it must pass on an exact copy of the DNA to function correctly.

DNA replication Therefore, DNA is copied (replicated) during the S phase of the cell cycle (part of interphase, before mitosis/meiosis)

Fill It In … Enzyme Review! What are enzymes? How do enzymes work?

DNA Replication Large team of enzymes coordinates replication Let’s meet the team… DNA Replication Large team of enzymes coordinates replication Enzymes more than a dozen enzymes & other proteins participate in DNA replication

Process of DNA replication An enzyme breaks the weak hydrogen bonds between the paired nitrogen bases. This allows DNA to “unzip” as the two strands move apart.

Replication: 1st step Unwind DNA helicase enzyme unwinds part of DNA helix stabilized by single-stranded binding proteins helicase single-stranded binding proteins replication fork

Process of DNA replication The newly unpaired nucleotides are paired (A-T and G-C) with extra nucleotides present in the nucleus. This process is catalyzed by another enzyme.

Process of DNA replication Enzymes then link the nucleotides along the newly constructed side of the DNA ladder by bonding sugar to phosphate.

Replication: 2nd step Build daughter DNA strand add new complementary bases DNA polymerase III Where’s the ENERGY for the bonding! But… We’re missing something! What? DNA Polymerase III

Replication Adding bases 5 3 energy DNA Polymerase III Adding bases can only add nucleotides to 3 end of a growing DNA strand need a “starter” nucleotide to bond to strand only grows 53 energy DNA Polymerase III DNA Polymerase III energy DNA Polymerase III The energy rules the process. energy B.Y.O. ENERGY! The energy rules the process 3 5

Replication fork / Replication bubble 5 3 3 5 DNA polymerase III leading strand 5 3 5 3 5 5 3 lagging strand 5 3 5 3 5 3 5 lagging strand leading strand growing replication fork growing replication fork 5 leading strand lagging strand 3 5 5 5

Starting DNA synthesis: RNA primers Limits of DNA polymerase III can only build onto 3 end of an existing DNA strand 5 5 3 5 3 5 3 3 growing replication fork 5 3 primase 5 DNA polymerase III RNA RNA primer built by primase serves as starter sequence for DNA polymerase III 3

Replacing RNA primers with DNA DNA polymerase I removes sections of RNA primer and replaces with DNA nucleotides DNA polymerase I 5 3 ligase 3 5 growing replication fork 3 5 RNA 5 3 But DNA polymerase I still can only build onto 3 end of an existing DNA strand

Process of DNA replication The DNA is proofread by enzymes for any errors.

Editing & proofreading DNA 1000 bases/second = lots of typos! DNA polymerase I proofreads & corrects typos repairs mismatched bases removes abnormal bases repairs damage throughout life reduces error rate from 1 in 10,000 to 1 in 100 million bases

Result of DNA replication Two identical DNA molecules have been produced. Each “daughter” DNA molecule is composed of one “old” strand and one “new” strand (Here a “strand” refers to one chain of nucleotides)

Result of DNA replication Each copy of DNA is packaged as a chromatid on a doubled chromosome.

Result of DNA replication After mitosis, each daughter cell will receive one of the two identical copies of DNA. This happens when the doubled chromosome is split, each new chromosome going to a new daughter cell. DNA Replication Amoeba Sisters

Fill It In … Replication What? Where? Used for? When?

Check Yourself! Why does each cell need DNA? What is the name of the process which makes a copy of DNA? When does DNA replication occur? What catalyzes each step of DNA replication? At the end of DNA replication, each molecule is composed of one _____ strand and one _____ strand.

Check Yourself! Why does each cell need DNA? TO MAKE NECESSARY PROTEINS What is the name of the process which makes a copy of DNA? When does DNA replication occur? What catalyzes each step of DNA replication? At the end of DNA replication, each molecule is composed of one _____ strand and one _____ strand.

Check Yourself! Why does each cell need DNA? TO MAKE NECESSARY PROTEINS What is the name of the process which makes a copy of DNA? REPLICATION When does DNA replication occur? What catalyzes each step of DNA replication? At the end of DNA replication, each molecule is composed of one _____ strand and one _____ strand.

Check Yourself! Why does each cell need DNA? TO MAKE NECESSARY PROTEINS What is the name of the process which makes a copy of DNA? REPLICATION When does DNA replication occur? INTERPHASE/S-PHASE OF INTERPHASE What catalyzes each step of DNA replication? At the end of DNA replication, each molecule is composed of one _____ strand and one _____ strand.

Check Yourself! Why does each cell need DNA? TO MAKE NECESSARY PROTEINS What is the name of the process which makes a copy of DNA? REPLICATION When does DNA replication occur? INTERPHASE/S-PHASE OF INTERPHASE What catalyzes each step of DNA replication? ENZYMES At the end of DNA replication, each molecule is composed of one _____ strand and one _____ strand.

Check Yourself! Why does each cell need DNA? TO MAKE NECESSARY PROTEINS What is the name of the process which makes a copy of DNA? REPLICATION When does DNA replication occur? INTERPHASE/S-PHASE OF INTERPHASE What catalyzes each step of DNA replication? ENZYMES At the end of DNA replication, each molecule is composed of one OLD strand and one NEW strand.