CHAPTER 11: DNA AND GENES

11-1 – DNA: The Molecule of Heredity

WHAT IS DNA? DNA ultimately determines an organism’s

trait. Achieves control by producing proteins

Example: Skin, muscle, bone, hair, enzymes, etc. Enzymes (protein) control the chemical

reactions needed for life. DNA contains the information – the

instructions for manufacturing all proteins.

THE STRUCTURE OF DNA DNA = Deoxyribonucleic Acid VERY long molecule Polymer made of repeating

subunits/nucleotides. Nucleotides have 3 parts:

Sugar – Deoxyribose Phosphate Group Nitrogen Base

4 Types of Nitrogen Bases: Adenine (A) Cytosine (C ) Guanine (G) Thymine (T)

DNA Backbone – Phosphate and Sugar Nitrogen bases stick out of the backbone like

teeth on a zipper.

DNA STRUCTURE CONTINUED Chargoff’s Rule:

The amount of Adenine (A) is always found in equal amounts to Thymine (T).

The amount of Cytosine (C ) is always found in equal amounts to Guanine (G).

Forming Complementary Base Pairs. 1953 – Watson and Crick proposed that DNA

is made of 2 chains of nucleotides joined together by Nitrogen bases that are held together by a hydrogen bond (weak bond).

DNA’s shape is a double helix

WHAT ABOUT ROSLIND FRANKLIN?

THE IMPORTANCE OF NUCLEOTIDE SEQUENCES All organisms have DNA made of the same 4

Nitrogen bases. How can organisms be so different from each other

if their genetic material is made of the same 4 nucleotides? Different sequences of nucleotides ATTGAC carries different information from a sequence

that reads TCCAAA. The closer the relationship between 2 organisms

the greater the similarity in their order of DNA nucleotides.

Used to determine whether 2 people are related or if a blood sample matches the DNA of a suspected criminal.

DNA REPLICATION Each cell has a copy of DNA. DNA is in the chromosomes and is copied during DNA

Replication. Each strand of DNA serves as a pattern to make a new

DNA molecule. Step by Step:

An enzyme breaks the H bonds between N bases that are holding them together. (Unzipping the DNA)

As the DNA unzips nucleotides that are floating free in the surrounding medium (cytoplasm) bond to the open single strand of DNA by base pairing.

Another enzyme bonds to the newly made strand and “proof-reads” the nucleotides to make sure no mistakes were made.

The process continues until the entire molecule has been unzipped and replicated.

The new strand is formed and is the complement of the original “parent” DNA strand.

LET’S PRACTICE DNA REPLICATION

ATT GAC CAT TAC AAC CGT GTA GGG AGC TAA CTG GTA ATG TTG GCA CAT CCC TCG

TTA CGG ACC TCG ACG TAA CTC GTT AAA AAT GCC TGG AGC TGC ATT GAG CAA TTT