C 4.1/4.2 What IS DNA & How DNA Works
- Chromosomes contain genetic info that determines inherited
characteristics
 Made of protein & DNA
 Can divided into sections, or
genes, based on instructions
for inherited traits
- DNA
 Lg. molecule that contains genetic info of organism
 Fd. in cells of ALL organisms
 Each organism has own unique DNA
 Has information that determines inherited traits for each
living organism
- Structure
 Made of nucleotides = base + sugar + phosphate
 4 bases: adenine, thymine, guanine, cytosine
 DNA base-pair rule: adenine always pairs w/ thymine;
guanine always pairs w/ cytosine
 Strand of DNA looks like a twisted ladder: double helix
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 DNA strands are bundled into structures called chromosomes
 DNA coiled tightly around proteins
 # of chromosomes differs w/ each type of organism
 Each human cell has 46 chromosomes (23 pairs)
 DNA is copied every time a cell divides
 Each DNA is divided into multiple genes
 Gene - a set of instructions for assembling a protein
 Each gene is a string of nucleotides
 Grouped by 3 base-pairs for each a.a. code
 Give cells info about how to make a specific protein
for specific traits (ex: curly hair; dimples)
 Each DNA can contain lg variety of genes: several hundred
to over 1 million
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- Genes and protein synthesis
 Each gene is a set of instructions for making one protein
 4 DNA bases (A, T, C, G) form “code” for making amino acids
 Each group of 3 bases is code for one specific a.a.
 Long sequence string of a.a. code linked together create
the code for making a protein
 20 different a.a.’s to that can be used to make proteins
 1000’s of genes code for 1000’s of different kinds of proteins
 Proteins are fundamental to cell function and processes:
 Act as chem. triggers
 Messengers for many processes w/in cell
 RNA molecules, messenger RNA, help convert DNA code into
protein in cell’s ribosomes – organelle in cytoplasm that makes
proteins from amino acids
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- Genetic mutations
 Mutation –  in #, type, or order of nucleotide-base sequence
 Cause cells to produce an incorrect protein during protein
synthesis; altered protein may not work properly
 Possible consequence:
 Improved trait, OR
 No change, OR
 Harmful trait
 Mistake often are corrected by cell, otherwise becomes part of
genetic message
ex: mutation in skin cell
 Mutations in sex cells can be passed from one generation to
next
ex: double-jointed, color blindness, sickle cell anemia, antibioticresistant bacteria, tusk-less elephants, cancer
- Genetic advancements
 Genetic engineering - process of ∆’g genes of living org.’s
 Create new products: drugs, foods, fabrics
 Bacteria often used to produce new proteins ex: insulin
 Plants – make more resistant to weather, bugs, disease
 Gene therapy – altering of DNA to treat genetic disorders
 Concerns of long-term effects & further mutations
 Genetic identification
 DNA fingerprinting – unique pattern in individual’s DNA
 No 2 people have same DNA except…
 Only identical twins have identical DNA
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 Used to ID family relations & hereditary diseases
 Missing persons & CSI application – ID remains, crime
scene presence
 Organism classification – how to classify new organisms
ex: algae no longer in plant kingdom
 Cloning used to produce offspring w/ desired traits
 Clone – organism that has exactly same genes as
organism from which it is produced
 Controversial – fears of human cloning