Chapter 12: DNA The Molecule of Heredity

Rosalind Franklin, Maurice Wilkins

______ _______ and _______ _____ (director) studied the structure of DNA crystals using X ray diffraction

Watson & Krik

had access to Franklin data; credited with 1951 DNA structure discovery

nucleotides

DNA consists of ________

1. a phosphate group

2. a deoxyribose sugar

3. one of 4 nitrogen bases

each nucleotide has three parts:
1. 
2.
3.

1. adenine

2. guanine

3. thymine

4. cytosine

4 nitrogen bases:
1. (A)
2. (G)
3. (T)
4. (C)

purines

Adenine (A) and Guanine (G) both consist of two fused five and six member rings of carbon and nitrogen atoms

pyrimidines

Thymine and Cytosine consist of a single six member ring with different functional groups attached

James Watson, Francis Crick

wilkins shared the x-ray data with _____ ______ and ______ ________

sugar phosphate backbone
sugars, phosphates

the phosphate group of one nucleotide bonds to the sugar of the next nucleotide in the same strand producing a ______ ______ ________ of covalently bonded ______ and _________; two strands are oriented antiparallel

ladder

two strands of DNA are assembled like a _______

sugar phosphate backbones

the outside of the ladder

complementary base pairs

A-T, G-C pairs

double

A to T are _____ bonded

triple

G to C are ______ bonded

1953

Watson and Erik announced they determined the structure of DNA in

genome

the complete sequence of DNA in an organism

mitosis

each daughter gets a copy of DNA in cells reproduced by

first step of replication

enzymes pull apart the parental DNA double helix, so that the two strands are no longer bonded together

second step of replication

enzymes, called DNA polymerases, move along each separated parental DNA strand, pairing up bases on the parental strands with complementary free nucleotides, forming new phosphodiester bonds between the phosphate of new nucleotide to sugar of previous

repair enzymes

proofread each daughter strand during and after replication

mutagens

________ may also cause mutations

point mutations

happen when just ONE base pair is changed

substitution mutation

changes a single base pair (of nitrogenous bases) to a different base pair

insertion mutation

occurs when one or more nucleotide pairs are inserted into the DNA double helix

deletion mutation

occurs when one or more nucleotide pairs are removed from the double helix

codon

three nucleotides of RNA read by ribosome as one unit (3 bases correspond to ONE amino acid)

inversion

occurs when a piece of DNA is cut out of a chromosome, turned around, and reinserted into the gap

translocation

occurs when a chunk of DNA is removed from one chromosome and attached to another

reproductive cells

in multicellular organisms mutations affect evolution only if they occur in ________ _____