c hapter 11: dna and g enes 11-1 – dna: the molecule of heredity
TRANSCRIPT
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
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.