Structure and Replication

6.A: Students will identify components of DNA, and describe how information for specifying traits of an organism is carried in the DNA 6.B: Students will recognize that components of that make up the genetic code are common to all organisms

DNA RNA Protein DNA is the molecule of heredity that passes from parents to offspring DNA contains the instructions for building proteins (which make up the structure of the body and carry out most of its functions) What are the functions of proteins? What are their monomers? Their elements?

In 1952, Rosalind Franklin used X-rays to photograph DNA molecules, but she could not interpret the photograph. Franklin s photograph helped James Watson and Francis Crick figure out the structure of DNA in 1953. The structure is called a double helix, or twisted ladder.

All living organisms contain DNA The structure of DNA is the same in ALL organisms only the order of nucleotides is different Which biomolecule is DNA? What is the monomer? The elements?

DNA is made of nucleic acids, which are made up of the subunit nucleotides (CHONP) Consists of (1) a phosphate group, (2) a 5 carbon sugar (deoxyribose), and (3) one of four nitrogenous bases

The two sides of the DNA molecule are called the backbone, are made from deoxyribose sugar and phosphate, joined by phosphate bonds The backbone is what gives DNA its double helix shape and structure (called the sugar-phosphate backbone) The two sides of the ladder run in opposite directions (antiparallel) One side runs 5 3 The other side runs 3 5

The center of the DNA molecule contains pairs of nitrogenous bases connected by hydrogen bonds DNA has 4 kinds of nitrogenous bases: Adenine, Guanine, Cytosine and Thymine The bases on one side of the ladder pair up with the bases on the other side Chargraff s Base Pairing Rules Adenine only pairs with Thymine (2 H-bonds) Guanine only pairs with Cytosine (3 H-bonds) A/T + G/C = 100%

The nitrogenous bases can be put into two categories Purines 2-carbon nitrogen ring Pyrimidines 1-carbon nitrogen ring

*The sequence of these bases determines your traits!!!

GATTACA

GATTACA CTAATGT

DNA: the molecule that carries the genetic instructions for the characteristics and traits of an organism Gene: a section of DNA that codes for a specific RNA or protein; a specific sequence of bases Chromosome: a single molecule of coiled (organized) DNA Genome: an organism s complete set of DNA, including all genes

ALL your cells contain a complete copy of your ENTIRE genome (except sex cells) Humans have 23 pairs of chromosomes (or 46 total) in each cell One set of 23 chromosomes from your mom (egg), and another set from your dad (sperm) There are approximately 20,000-30,000 genes on a human chromosome, and each gene has about 6 billion base pairs (seemingly infinite combinations)

ALL organisms (animals, plants, fungi, protists, and bacteria) have DNA made out of the same components Sugar-phosphate backbone The 4 nitrogenous bases (A, C, G, and T) There are only two differences in the DNA of different organisms Different organisms have different number of chromosomes Bacteria have one chromosome Eukaryotes have 10-50 chromosomes The order (sequence) of bases is different for each organism

1. In DNA replication, the enzyme helicase splits the double helix down the middle by cutting the hydrogen bonds 2. Once separated, each side is used as a template strand and the enzyme RNA primase adds an RNA primer to each strand of DNA 3. The enzyme DNA polymerase adds the matching bases to the RNA primer on each template strand The leading strand is made as nucleotide bases are added smoothly to the 3 end The lagging strand is made as nucleotide bases are added in the 3 5 direction with small pieces called Okazaki fragments

A 1. A 2. E 3. e 4. DNA polymerase then removes the RNA primers and replaces them with DNA nucleotides 5. The enzyme ligase seals the bonds between the bases 6. The end result is two IDENTICAL molecules of DNA identical to each other and identical to the original

Once replication is finished, there are two complete double helix molecules of DNA Each new double-helix molecule has one old strand and one new strand The old strand is said to have been conserved Semi = half Therefore, this type of replication is known as semi-conservative

1. The double helix unzips This unzipping is caused by the enzyme helicase

2. The two strands are separated

3. Each side is now a template The addition of new DNA bases onto the two original strands of DNA is performed by the enzyme DNA polymerase The bonds between the old and new bases is sealed by the enzyme ligase

3. Each side is now a template Because the two strands are antiparallel, one goes in the direction of replication (leading strand), and the other does not (lagging strand)

3. Each side is now a template Replication occurs continuously for the LEADING strand Bases are added to the 3 end

3. Each side is now a template Replication occurs discontinuously, in short sections, in the LAGGING strand (3 5 ) These sections are known as Okazaki fragments

3. Each side is now a template

4. The result is two IDENTICAL strands of DNA

One strand is the original strand (PARENT) One strand is the new strand (DAUGHTER)

All cells contain ALL your DNA However, different genes are turned on in different cells This means different proteins are made in each cell whatever the cell needs to make in order to do its job This is a regulated process (what biomolecule?)

Cell Differentiation All cells start as stem cells - undifferentiated Different cells have different jobs, so stem cells have certain genes that get turned on the ones that help the cell do its job

Cell Differentiation Examples animal cells Blood: carries oxygen to cells (RBC) and fights infection (WBC) Muscle: allows movement (skeletal, smooth, cardiac) Epithelium: skin, secreting mucus, & absorbing nutrients

Cell Differentiation Examples plant cells Root: absorb water and minerals from the soil Stem: carry substances between roots and leaves Leaves: capture sunlight and perform photosynthesis