DNADNA

Deoxyribonucleic AcidDNA is found:In the nucleusIn mitochondria and chloroplasts

Functions of DNA: Control functions of cell by controlling protein production

Pass on hereditary information to the next generation

General Structure of DNAGeneral Structure of DNA Polymer, with many repeating units called Polymer, with many repeating units called

nucleotidesnucleotides Subunits:Subunits:

a five carbon sugara five carbon sugar DeoxyriboseDeoxyribose

a phosphate groupa phosphate group a nitrogenous base a nitrogenous base

AdenineAdenine ThymineThymine GuanineGuanine CytosineCytosine

(guanine, cytosine, adenine thymine)

(Deoxyribose)

General Structure of DNAGeneral Structure of DNANucleotides form

long chains between the phosphate

groups and the #3 carbon of the sugar molecule

This is called the backbone

Structure of DNAStructure of DNAThe bases pair up and are held together with The bases pair up and are held together with

hydrogen bonds:hydrogen bonds:

G (guanine) G (guanine) always pairs always pairs with with

C C (cytosine)(cytosine)

A (adenine) A (adenine) always pairs always pairs with with T (thymine)T (thymine)

G always binds to CA always binds to TP

DA

P

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A and T as well as C and G are called

complementary base pairs

Humans have about 3 billion (that is 3,000,000,000) base pairs

Structure of DNAStructure of DNA

Two polymer Two polymer chains are chains are

connected by connected by weak weak

hydrogen hydrogen bonds and are bonds and are twisted into a twisted into a double helixdouble helix

Why?

To repair damage and grow, new cells are made.

Each new cell needs to have a complete DNA record

DNA ReplicationDNA Replication

The Cell copies its own DNA

Basic Steps of Replication:

•Unwinding – DNA strands uncoil and separate

•Synthesis – complementary sequence of nucleotides are

made along each original strand

DNA ReplicationDNA Replication

P

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unwinding

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Complementary base pairing

A

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Complementary base pairing

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New strands

DNA ReplicationDNA Replication

Each new DNA contains one of the strands from the original DNA and a completely new strand

This is called semi-conservative

replication

DNA Replication: The DetailsDNA Replication: The Details

•occurs at more than one place along the molecule•forms replication bubbles and replication forks•speeds the process – replicates multiple areas at the

same time•Helicase – Enzyme that unwinds and separates DNA

Unwinding and separating

DNA Replication: The DetailsDNA Replication: The Details

RNA Primase adds a starter strip to the DNA

DNA polymerase adds a new nucleotide to the new strand at the #3 carbon

Synthesizing New Strands

DNA polymerase then replaces the RNA bases on the primer strips with DNA bases

The enzyme Ligase joins the ends of the sections

DNA Replication: The DNA Replication: The DetailsDetails

DNA is replicated continuously in one direction and discontinuously in the other

The short strips are called Okazaki fragments

DNA Replication: The DetailsDNA Replication: The Details

Two molecules of DNA are created through replication

http://www.fed.cuhk.edu.hk/~johnson/teaching/genetics/animations/dna_replication.htm

Protein synthesis:

•Occurs in the cytoplasm at the ribosomes

•Creates polymers from amino acids by dehydration synthesis

•Is directed by DNA in the nucleus

•Requires RNA – mRNA and tRNA

•Involves two main steps – Transcription and Translation

From DNA to ProteinFrom DNA to Protein

RNA StructureRNA Structure

NucleotideNucleotide Sugar – RiboseSugar – Ribose Phosphate groupPhosphate group Nitrogenous BasesNitrogenous Bases

Adenine, Guanine, Adenine, Guanine, Cytosine, Cytosine, UracilUracil

Single stranded - Single stranded - does not form a double helix

RNA StructureRNA Structure

DNADNA RNARNA

Double strandedDouble stranded

Sugar = deoxyriboseSugar = deoxyribose

Bases = A, T, C, GBases = A, T, C, G

Single strandedSingle stranded

Sugar = riboseSugar = ribose

Bases = A, Bases = A, UU, C, G, C, G(Uracil instead of (Uracil instead of

Thymine)Thymine)

Types of RNA:

1) messenger RNA (mRNA): formed during transcription transports code for protein to cytoplasm 

2) transfer RNA (tRNA): carries amino acids binds to mRNA during translation, forming protein

3) ribosomal RNA (rRNA): comprised of 2 subunits holds the tRNA and mRNA during translation

RNA StructureRNA Structure

Transcription:

•Cell makes RNA code for amino acid sequences

•Occurs in nucleus

Translation:

•Cell constructs protein molecule using RNA

•Occurs in the cytoplasm

Protein SynthesisProtein Synthesis

TranscriptionTranscriptionDNA mRNA

DNA Unwinds

RNA base pairs are added to one side of the DNA

Pairs: C-G T-A A-U

The new RNA strand is called messenger RNA

(mRNA)

TranscriptionTranscription

RNA Processing:RNA Processing:

DNA has spacers between its information areas

The spacers are called introns The information areas are called exons

exon exonexonintron intron

Transcription - Transcription - RNA RNA ProcessingProcessing

•RNA is capped on both ends –

(modified guanine on one end - a string of adenosines called

poly-A on the other)

•The introns are removed

•The exons are spliced together

Ready to move to the Ribosomes!

Translation Translation

mRNA has the mRNA has the coded information coded information

A sequence of A sequence of three bases three bases (codon) codes for a (codon) codes for a specific amino acidspecific amino acid

P

RA

P

RU

P

RG

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RC

Codon

mRNA

TranslationTranslationThe codons must be translated into the

proper amino acid. (Don’t worry – they made a

chart.)

TranslationTranslation

tRNA (transfer RNA):

•amino acid carriers – brings amino acids to ribosomes one by one

•anti-codon – complementary bases on tRNA that pair to mRNA codon

The anticodon fits the codon of the mRNA

TranslationTranslation

Ribosomes are made up of one large and one small subunit

The mRNA binds where the subunits meet

Sub Units

mRNA

TranslationTranslation

tRNA molecules bring amino acids to the ribosome following the order of the codons of the mRNA

Each amino acid is added to the growing polymer by dehydration synthesis

Next amino acid

Ribosomes can form an assembly line and follow each other down the mRNA strand, starting another protein before the first one is finished.

TranslationTranslation

Strings of polypeptides come streaming out of the ribosome units

When the protein is complete, the mRNA and ribosome separate

Protein Synthesis:

Errors in decoding cause mutations that can be passed along to the next generation

A difference of one amino acid changes the shape of normal hemoglobin and causes sickle cell anemia

Translation RecapTranslation Recap

What you need to know:• Characteristics of DNA • Characteristics of RNA • Know the complementary base pairs for DNA and RNA• What is replication, when does it occur (or why is it

important)? • Be able to describe the replication process• Be able to describe the protein synthesis process.

Know the two steps and where each step takes place.• Know the difference between mRNA, tRNA and rRNA

and how each one is used in protein synthesis.