DNA LS 5.3

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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)