Understanding DNA: Structure, Function, and Replication

Genetics

the study of genes and heredity

Trait

inherited characteristic determined by the presence and expression of dominant and/or recessive alleles

Gene

a segment of DNA that codes for protein, which in turn codes for a trait (skin tone, eye color, etc.)

Chromosomes

structures made of DNA

Deoxyribonucleic acid (DNA)

molecule that stores genetic information in cells

DNA replication

the process by which DNA copies itself exactly for new cells

Blueprint of life

a term often used to describe DNA

Cell types controlled by DNA

muscle cell, blood cell, nerve cell

Proteins

responsible for all cell structures and functions

Amino acids

the building blocks of proteins, of which there are 20 in the body

Importance of DNA study

essential to all life on earth with medical benefits including disease detection, treatment, and prevention

Forensics

the application of DNA study for identifying crime

DNA Structure

a very large molecule made up of a long chain of sub-units (nucleotides)

Nucleotides

the building blocks of DNA

Nitrogenous Bases

the four bases in DNA: Adenine (A), Thymine (T), Cytosine (C), Guanine (G)

Adenine and Guanine

nitrogenous bases that each have two rings of carbon and nitrogen atoms

Thymine and Cytosine

nitrogenous bases that each have one ring of carbon and nitrogen atoms

Base Pair Rule

Adenine can bond only with Thymine and Cytosine can bond only with Guanine

Complimentary strands

the concept that two DNA strands can pair up based on base pairing rules

Double Helix

the structure formed by double-stranded DNA

DNA Strand

formed by nucleotides bonding to each other

Replication

The process by which DNA makes a copy of itself.

RNA

Ribonucleic Acid.

Why does DNA Replicate?

Cells copy genetic information before cell division (in s phase of interphase) so that each new cell has a complete set of DNA.

How does DNA Replicate?

1. Unwind - Topoisomerase unwinds the coiled strands of DNA. 2. Unzip - DNA Helicase 'unzips' the strands of DNA, breaking the hydrogen bonds, and creating two template (parent) strands for replication. 3. Hold Open - Single-Strand Binding Proteins (SSBs) keep the strands separated. 4. Base Pairing - DNA Polymerase III bonds free nucleotides with nucleotides on each template (parent) strand using base pairing rules. 5. Proofread - DNA Polymerase I proofreads new strands and backtracks to correct errors. 6. Joining Nucleotides - DNA Ligase bonds the backbone together (glues the Okazaki Fragments from the lagging strand together).

Replication Results

2 identical DNA molecules, each with an old strand and a new strand.

Semi-conservative replication

Having old strand and new strand.

Anti-Parallel Strands

Both DNA strands run anti-parallel to each other (oriented in opposite directions). One strand is 5 prime to 3 prime (5' - 3'), the other is 3' - 5'.

Replication Fork

Directional movement of replication.

Polymerase III

Only works in 5' to 3' direction on BOTH parent strands.

DNA Replication location

Takes place in the nucleus of eukaryotic cells and in the cytoplasm of prokaryotic cells during interphase (before the cell divides).

Why did Hershey and Chase use radioactive markers?

The isotopes acted as labels to trace which molecules entered bacteria.

Who determined that DNA holds genetic information?

Oswald Avery.

Primary purpose of Frederick Griffith's experiment

To identify the molecule responsible for heredity in bacteria.

Structure of RNA

Consists only of one strand of nucleotides.

Sugar in RNA

Has ribose (a 5C sugar) NOT deoxyribose.

Nitrogenous base in RNA

Has uracil (U) as a nitrogenous base NOT thymine.

DNA structure

Sides of the ladder alternate phosphate and sugar (deoxyribose).