DNA Structure & Function

Chapter 12Random Chapter 13

dna– Has the capacity to store genetic information– Can be copied and passed from generation to

generation– Located in the nucleus of cells– “blueprint” of life

Nucleic acids• Information storage molecules• Directions for building proteins• Found in nuclei of eukaryotes• Two forms

– Deoxyribonucleic acid – Ribonucleic acid

• Polymers of nucleotides

DNA Nucleotide• 5 Carbon sugar

– Deoxyribose– ribose

• Phosphate group• Nitrogenous base

– Adenine– Guanine– Cytosine– Thymine (DNA only)– Uracil (RNA only)

RNA Nucleotide• Sugar-phosphate backbone • Ribose sugar• Complementary Nucleotides

– Uracil (u)– Cytosine (c)– Adenine (a)– Guanine (g)

• RNA has uracil in place of thymine• Single strand• Information transfer and translation

DNA structure• Sugar-phosphate backbone

– Deoxyribose sugar– Covalent bonds

• Complementary Nucleotides– Pyrimidine

• Thymine (T)• Cytosine (c)

– Purine• Adenine (a)• Guanine (g)

• Double helix– Hydrogen bonds

Complementary Base Pair Rule

G-C A-T A-U in RNA

DNA Replication • Template mechanism • DNA strand is unwound and double helix

is separated• Single strand replicated via base pair rule

DNA Function– Stores genetic information– Instructions for all life and life processes

• Contains protein building instructions– Uses specific code built into sequence of

nucleotides

Genetic Code• Genes have nucleotide code for building proteins

– Proteins are made of amino acids• The set of rules giving the correspondence between

nucleotides of nucleic acids and amino acids of proteins• Codon aka Triplet Code

– Sets of 3 nucleotides

Genetic Code

• Each codon represents an amino acid

• Code is redundant• Specific Start & stop

codons• Code is universal to life

Terminology• Gene

– Sequence of nucleotides that is the unit of hereditary information

– Ie. A recipe• Genome

– The sum of an individuals genes

Genes are made of Introns & exons

– Exons • Segments of DNA that

code for AA– Introns

• Sections of nucleotides that do not code for AA

• Regulatory function

Why are proteins so important?

remember…..

Protein Types• Structural• Storage• Contractile• Transport• Defense• Signal• Enzymes

• The one gene–one protein hypothesis states that the function of an individual gene is to dictate the production of a specific protein

Junk DNA

Gene Expression • How dna’s instructions are carried out• This is how genes control the structures and activities

of cells• Code in gene is copied and used to build proteins or run

other jobs

In Animal Cell… DNA is Isolated in the Nucleus

Protein Building Structures in cytoplasm

Transcription vs Translation

• Transcription• Transcription occurs in the nucleus

• Translation• Translation occurs in the cytoplasm

Uses DNA and RNA

Transcription• Converts DNA to RNA

– Results in strand of messenger RNA (template)

– Uses Complementary base pair rule

• Region of copying unwinds & then rewinds after mRNA is complete

Messenger RNA (mRNA)• RNA Template of DNA • Single strand of nucleotides• Uses Uracil instead of Thyamine• Moves from inside nucleus to

cytoplasm

mRNA Is Processed• MRNA is spliced (cut &

paste)– Introns removed

DNA

RNAtranscriptwith capand tail

mRNA

Introns removed Tail

Exons spliced together

Coding sequence

Nucleus

Cytoplasm

TranscriptionAddition of cap and tail

Translation– Converts from nucleic

acid (nucleotide) language to the protein language (amino acid)

– Converts mRNA to protein

Transfer RNA (tRNA)• Molecular translators• Carries specific amino

acid• Matches codon in

mRNA using anticodon• Recycled after each use

Ribosomal RNA

tRNAbinding sites

P site A siteLargesubunit

mRNAbindingsite

Smallsubunit

P site A site

P A

– Site of protein synthesis– Made up of ribosomal RNA (rRNA)– Holds mRNA & tRNA

Mutagen

• Physical or chemical agents that induce change in nucleotide sequence of DNA (aka Mutation)

• Physical– Radiation– X-ray, uv light

• Chemical– carcinogens

• Viral

Mutation• Mutation

– A change in the nucleotide sequence of a nucleic acid

• Point mutations– “switch” nucleotide

• Frame shift mutations– Insertion- add extra nucleotides– Deletions- delete nucleotide

Mutation• Good or bad• Beneficial/ adaptive• deleterious

Epigenetics

• Study of heritable changes in gene expression caused by mechanisms other than DNA sequence

• http://video.pbs.org/video/1525107473/

Lyonisation• Mary Lyon 1962• In Females each somatic cell has 2 X chromosomes

– One X chromosome is inactivated– Random inactivation

• Shortened and condensed• Females are genetic mosaics

Lyonisation

• Occurs only in females• X chromosome has fur color

control gene• 2 alleles

– Black & Orange• White results from genetic

condition of unpigmented hair