What is DNA Deoxyribonucleic Acid The hereditary material This is what you get from your parents and what is passed to offspring during reproduction A type of nucleic acid recall 4 main biological molecules ID: 583468
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Slide1
DNA
LS 5.3Slide2
What is DNA?
Deoxyribonucleic Acid
The
hereditary
material
This is what you get from your parents, and what is passed to offspring during reproduction
A type of
nucleic acid
(recall 4 main biological molecules)
A characteristic of all living things
The smallest bacteria has DNA
DNA is very similar between organisms
Evidence for common ancestry
Contains the
instructions for the organism
Called
genesSlide3
DNA, Chromosomes and Genes
DNA
is the hereditary material
Usually long and stringy (chromatin)
Wraps around proteins during cell division (
chromosomes)A segment of DNA that contains instructions is called a gene Slide4
Discovery of DNA
People knew something existed that passed traits on, but didn’t know what it was.
Mendel called them factors
Darwin said something would be found that explains how traits are passed
In the early 1900’s, DNA was suspected to be the hereditary material
Rosalind Franklin and Maurice Wilkins
Took
X-ray
photographs of DNAJames Watson and Francis CrickTook Franklin and Wilkins’ work and discovered the structure of DNASlide5
Structure of DNA
DNA is a chain of
smaller units
Like links on a chain
Looks like a twisted ladder
Called a double helixThe smaller units are called nucleotides
A nucleotide is made up of 3 parts
The backbone is made of:
A sugar, called deoxyriboseA phosphate groupThe interior (rungs of the ladder) have:Nitrogen basesSlide6
Nitrogen Bases
4 of them
Adenine (
A
), Thymine (
T), Guanine (G), Cytosine (C)
Their
sequence
determines the geneBases come in pairsThey are held together by bondsThey give the DNA molecule its shapeA-T (apple tree)
C-G (car garage)Slide7
DNA Replication
Occurs whenever the
cell splits
(mitosis: recall S-phase)
DNA
unzips (just like a zipper) and splits apartEach ½ provides a template to form another identical molecule
Example: Find the complementary strand
A G T C G A
T C A G C TSlide8
RNA
Another nucleic acid
Ribonucleic Acid
Similar to DNA, but key differences
Where DNA has 2 sides, RNA is
single-sidedWhere DNA has deoxyribose as its sugar, RNA has riboseWhere DNA has Thymine (T), RNA replaces it with
Uracil (U)
T DOES NOT EXIST IN RNA!Slide9
Types of RNA
mRNA
(messenger RNA)-carries message from nucleus to ribosomes
rRNA
(ribosomal RNA)-RNA in a ribosome that reads the code
tRNA (transfer RNA)-carries amino acid to ribosomeSlide10
Making a protein
Proteins are chains made of units called
amino acids
The
sequence of amino acids
determines the protein’s shapeThe shape determines the jobThe sequence of amino acids is determined by the gene
Better definition for gene:
a segment of DNA that codes for a specific protein
mRNA is made from a strand of DNA (Called transcription)Practice: What RNA strand would form from this DNA strand?A T G C G T AU A C G C A U
Because it is small, mRNA can leave the nucleusIt travels to a
ribosome, where
rRNA bonds to ittRNA
carries amino acids to the ribosome, and place them in the correct spot (
translation
)
The amino acids bond together, forming the
protein Slide11
Central Dogma of Biology
Dogma-an idea known to be true that is central to the field
DNA
RNA Proteins Traits Slide12
Mutations
Change in nucleotide sequence
on DNA
Different types
Nucleotides can be
deletedA wrong nucleotide can be addedThe wrong nucleotide
can replace the correct one
Chromosome parts can be
brokenCan be natural, or can be the result of a mutagen (something in the environment that causes a mutation)Smoking, alcohol, disease, excess sunlight, asbestos, etc. Slide13
Results of Mutations
Most mutations are
neutral
You’d never even know it happened
The cell repairs it, or it occurs in noncoding (junk) DNA
Other mutations are badCan lead to disease, such as cancerOccasionally, mutations are
beneficial
Give something to the offspring that they did not previously have
Example: Making an animal’s coat look a little more similar to its surroundingsThis is what natural selection acts on (more to come next chapter)