DNADNA

How are cells structured to How are cells structured to do the “right” thing?do the “right” thing?

Structure of DNAStructure of DNA

DNA is composed of:DNA is composed of: 2 sugar-phosphate backbones2 sugar-phosphate backbones 4 types of nitrogenous bases4 types of nitrogenous bases

AdenineAdenine GuanineGuanine ThymineThymine CytosineCytosine

DNA base-pairing rulesDNA base-pairing rules

A always pairs with TA always pairs with T G always pairs with CG always pairs with C

Provides a way for exact copies of Provides a way for exact copies of DNA to made DNA to made → DNA replication→ DNA replication

Important to keep genetic code the same when Important to keep genetic code the same when new cells are made!new cells are made!

DNA ReplicationDNA Replication

DNA strand is untwisted DNA strand is untwisted Bonds between b.p. are Bonds between b.p. are

brokenbroken Two new strands are Two new strands are

made by filling in made by filling in matching bases one at a matching bases one at a timetime

Result= 2 new identical Result= 2 new identical DNA strands!DNA strands!

DNA and the living cellDNA and the living cell

DNA DNA divided into segments called genesdivided into segments called genes Humans have over 20,000 genesHumans have over 20,000 genes Genes provides information for making Genes provides information for making

proteinsproteins

Genes and ProteinsGenes and Proteins

Each gene codes for a unique Each gene codes for a unique protein with specialized function in protein with specialized function in cellcell

All cells have the same set of genesAll cells have the same set of genes Different kinds of cells use different Different kinds of cells use different

combinations of genescombinations of genes Cells only build the proteins they need Cells only build the proteins they need

to do their job!to do their job!

Functions of proteins in Functions of proteins in cellscells

General functions:General functions: Enzymes (DNA polymerase)Enzymes (DNA polymerase) Transport proteins (Hemoglobin)Transport proteins (Hemoglobin) Cell signaling proteins (Insulin)Cell signaling proteins (Insulin) Structural proteins (Keratin)Structural proteins (Keratin)

Protein synthesisProtein synthesis

Cell follows TWO step process to Cell follows TWO step process to build proteins from DNAbuild proteins from DNA TranscriptionTranscription

Making a copy of the DNA (called Making a copy of the DNA (called messenger RNA) and sending that copy to messenger RNA) and sending that copy to the ribosomethe ribosome

TranslationTranslation Ribosome use information in the mRNA to Ribosome use information in the mRNA to

assemble the proteinassemble the protein

mRNA vs. DNAmRNA vs. DNA

Differences between DNA and Differences between DNA and RNARNA

RNA is…RNA is… Single-strandedSingle-stranded Different sugar (ribose)Different sugar (ribose) Thymine (T) is replaced by Thymine (T) is replaced by

Uracil (U)Uracil (U)

TranscriptionTranscription

Starts in the nucleusStarts in the nucleus DNA is unzippedDNA is unzipped Copy is made: messenger Copy is made: messenger

RNA (mRNA) with RNA (mRNA) with complementary basescomplementary bases

End result is single-End result is single-stranded mRNA that stranded mRNA that travels through the travels through the cytoplasm to the cytoplasm to the RIBOSOMERIBOSOME

TranslationTranslation

Occurs in ribosome (protein building Occurs in ribosome (protein building machinery)machinery)

Ribosome reads mRNA sequence 3 letters at Ribosome reads mRNA sequence 3 letters at a time (codon)a time (codon)

Each codon codes for a particular amino acidEach codon codes for a particular amino acid 20 possible amino acids20 possible amino acids

Order amino acids are assembled is different Order amino acids are assembled is different for all proteinsfor all proteins Sequence of a.a. determines shape of protein Sequence of a.a. determines shape of protein

which determines functionwhich determines function End result is a specific protein based on the End result is a specific protein based on the

original code!original code!

Genetic CodeGenetic Code