DNA and GenesDNA and Genes

Chapter 11

11-1 DNA: The Molecule of 11-1 DNA: The Molecule of HeredityHeredityObjectivesAnalyze the structure of DNADetermine how the structure of

DNA enables it to reproduce copies of itself

SCS: B-4.1

What is DNA?What is DNA?What influences what an organism looks like?◦Environment◦GenesFound in DNA (deoxyribonucleic acid)Makes protein

Structure of DNAStructure of DNApolymer of nucleotides (nucleic acid)

composed of a phosphate group, sugar (deoxyribose) , and a nitrogenous base

nucleotides come together held together by the phosphate groups at one end and by the bases in the middle

the structure resembles a ladder◦the bases make up the rungs and the sugar/phosphate group make up the sides of the ladder

◦Each side is complimentary to each other

In 1953, Watson and Crick proposed the shape of DNA to be a double helix

Types of BasesTypes of Bases

Purines:Adenine (A)Guanine (G)

Pyrimidines:Cytosine (C)Thymine (T)

The bases bond to each other in the center of the ladder with hydrogen bonds

The bases bond together is a certain way – base pairing rule:

A - T C - GThe amount of A = TThe amount of C = G

almost all organisms have the same bases A, T, C, G

what makes organisms different is the sequence of these letters in your DNA

each species has a unique sequence of DNA

some sequences are very similar – share a common ancestor

DNA ReplicationDNA Replication

How do new organisms get the DNA of their particular species?

DNA is copied or replicated during Interphase

Steps in ReplicationSteps in Replication

1. Enzymes break down the hydrogen bonds holding the bases together – unzips molecule

2. Free floating complimentary nucleotides are added to the exposed strand with another enzyme. (base pairing rules apply)

3. Process continues until the entire molecule is unzipped and replicated

4. The end result are two copies of the DNA molecule. Each molecule has one strand from the original DNA and a complimentary copy.

11-2 DNA to Proteins11-2 DNA to ProteinsObjectives

DNA codes for proteins

Proteins help cells function

Proteins are made of amino acids

The nucleotide sequence in DNA specifies the order of amino acids which make proteins

DNA>>>>amino acids>>Protein

RNA – Ribonucleic AcidRNA – Ribonucleic AcidDNA can not leave the nucleus, so a copy has to be made - RNA

the process of making a copy of DNA into RNA is called transcription

Detail of RNA (differing from Detail of RNA (differing from DNA)DNA)Single strand of nucleotides

Contains the sugar ribose

Made of the 4 nucleotides A, C, G, and U (replaces T since thymine is not ever found in RNA)

Pairing Rules for RNAPairing Rules for RNA

DNA RNAA --------------------------UT---------------------------AC---------------------------GG---------------------------C

Types of RNATypes of RNA

1. mRNA or messenger RNA – copy of DNA that leaves the nucleus.

2. tRNA or transfer RNA – carries amino acids to the ribosome

3. rRNA or ribosomal RNA- part of the ribosome complex

Steps in TranscriptionSteps in Transcription

1. DNA is unzipped with enzymes exposing the specific region needed.

2. Free floating bases are added to growing strand of RNA along with ribose and phosphate groups

3. The RNA strand grows until it reaches a special stop signal

4. RNA drops off and leaves the nucleus to the site of protein synthesis – ribosomes

5. DNA zips back up.

Genetic CodeGenetic Code

mRNA carries the genetic message

Message is made up of a language of nucleotides

◦Uses bases for the alphabet of amino acidsOnly 20 different amino acids are found

◦A 3 letter (base) sequence codes for a particular amino acid ----called a codon

There are codons for stopping the reading of the sequence called stop codons (UGA, UAA, UAG)

The sequence always begin at a special start codon – AUG (aa – methonine)

◦Use a “key” to determine what each codon codes for

◦All organisms use this same “key” or chart to determine the amino acids

TranslationTranslationProcess of translating the mRNA sequence into amino acids to make proteins

Takes place in ribosomes

StepsSteps1. mRNA attaches to ribosome2. - tRNA molecule brings first

amino acid to mRNA and attaches

- tRNA contains the anticodon (compliment to codon on mRNA)- the ribosome slides to the

next codon in the sequence

3. The next tRNA attaches to the mRNA along with its amino acid

4. When two tRNAs are in place, enzymes attach the two amino acids with a peptide bond

5. This process continues until a stop codon is reached on the mRNA

- The chain of amino acids now becomes a protein with a specific shape and function and goes where it is needed within the cell/body

MutationsMutations

a change in the DNAa change in reproductive cells can only be passed on to the next generation

changes can be bad, good, or have no affect at all

a change in body cells can not be passed on to the next generation

can cause cancer or cell death

Types of MutationsTypes of Mutations1. Gene level

◦ point mutation - change in a single base pair

i.e. The dog bit the cat.

Mutation The dog bit the car.

changes the meaning of the “sentence” which can result in the wrong protein

◦ frameshift mutation-a single base pair is added.

i.e. The dog bit the cat.

Mutation The dob itt hec at.

2. Chromosome level change in actual

chromosome due to nondisjuntion common in plants

TypesTypes Deletion- when part

of the chromosome is left out

Example:ABCDEFGH>>>>>>

ABCEFGH

insertion- when part of a chromatid breaks off and attaches to its sister chromatid

ABCDEFGH>>ABCBCDEFGH

inversion – when part of the chromosome breaks off and reinserts itself backwards

ExampleABCDEFGH>>>ADCBEFGH

translocation- when part of one chromosome breaks off and is added to a different chromosome

Example:ABCDEFGH>>>WXABCDEFGHWXYZ>>>>>> YZ

Causes of MutationsCauses of Mutationsmistake during replication

Environmental, UV, chemicals, pollutants, radiation, high temperatures etc. are mutagens (agent which can cause change in DNA)

DNA does a remarkable job repairing itself