Unit 1: Central Code and Genetic Material Paz Etcheverry NS 315

Unit 1: Central Code Unit 1: Central Code and Genetic Materialand Genetic Material

Paz EtcheverryPaz Etcheverry

NS 315NS 315

Topics to coverTopics to cover

Cell structureCell structure DNA structureDNA structure DNA replicationDNA replication RNA structureRNA structure The Central Dogma of BiochemistryThe Central Dogma of Biochemistry Transcription: DNA to mRNATranscription: DNA to mRNA Translation: mRNA to proteinTranslation: mRNA to protein Codons and anticodonsCodons and anticodons

Cell structureCell structure

The nucleus: contains23 pairs of chromosomes.DNA is arranged in thesechromosomes.Where replication and transcription occurs.

The ribosome: where protein is synthesized (i.e. translation occurs)

Cytosol or cytoplasm

DNA structureDNA structure

The nucleus: contains23 pairs of chromosomes.DNA is arranged in thesechromosomes

23 pairs of chromosomes:

http://ghr.nlm.nih.gov/handbook/basics/howmanychromosomes

How many chromosomes How many chromosomes does each human cell does each human cell have?have?Each human cell contains 46Each human cell contains 46

chromosomes:chromosomes:– 22 pairs of somatic (non sex) 22 pairs of somatic (non sex)

chromosomeschromosomes– 2 sex chromosomes:2 sex chromosomes:

Female sex chromosomes: 2 XFemale sex chromosomes: 2 X Male sex chromosomes: 1 X and 1 YMale sex chromosomes: 1 X and 1 Y

Inside each of the Inside each of the 23 pairs of 23 pairs of chromosome, there chromosome, there is DNA.is DNA.

DNA is tightly DNA is tightly packed inside each packed inside each of the of the chromosomes.chromosomes.

Each chromosome is Each chromosome is composed of two composed of two chromatids joined chromatids joined by a centromere.by a centromere.

Centromere

DNA

A chromosome pair

DNA DNA (deoxyribonucleic (deoxyribonucleic acid)acid)

Double helixDouble helix Double= 2 Double= 2

polynucleotide chainspolynucleotide chains Helix= helical Helix= helical

structure (like a structure (like a spring)spring)

Each chain contains Each chain contains nucleotides (joined to nucleotides (joined to each other) and a each other) and a sugar/phosphate sugar/phosphate backbonebackbone

http://instruct.westvalley.edu/svensson/CellsandGenes/dna-structure%5b1%5d.gif

Nucleotides in DNANucleotides in DNA

The nucleotides areThe nucleotides are– Adenine (A)Adenine (A)– Thymine (T)Thymine (T)– Cytosine (C)Cytosine (C)– Guanine (G)Guanine (G)

A binds to TA binds to T C binds to GC binds to G A and G= purine A and G= purine

basesbases T and C= pyrimidine T and C= pyrimidine

basesbases

http://instruct.westvalley.edu/svensson/CellsandGenes/dna-structure%5b1%5d.gif

Sugar backboneSugar backbone

Notice how the two sugar chains run opposite each other:

The 5’ end (which hasa phosphate group), faces the 3’ end (which has a hydroxyl (OH) group)and vice versa.

Who discovered the Who discovered the structure of DNA?structure of DNA? James Watson, a young American scientist and Francis James Watson, a young American scientist and Francis

Crick, a young English researcher. Crick, a young English researcher. In 1953, Watson and Crick published a paper in which In 1953, Watson and Crick published a paper in which

they proposed and described the structure of DNA.they proposed and described the structure of DNA. Rosalind Franklin (an English researcher) was within a Rosalind Franklin (an English researcher) was within a

couple days of coming to the same conclusion when couple days of coming to the same conclusion when their paper was published. their paper was published.

Watson and Crick received the Nobel prize in 1962. Watson and Crick received the Nobel prize in 1962. Rosalind Franklin died in 1958 of ovarian cancer, Rosalind Franklin died in 1958 of ovarian cancer,

probably due in large part to her work with x-rays. probably due in large part to her work with x-rays. Since the Nobel prize is not awarded posthumously, Since the Nobel prize is not awarded posthumously,

people have often wondered if the Nobel committee people have often wondered if the Nobel committee would have included Franklin if she had still been would have included Franklin if she had still been alive. alive.

http://biology.clc.uc.edu/courses/bio104/dna.htm

DNA replicationDNA replication

What is DNA What is DNA replication?replication?

DNA replication is a DNA replication is a fundamental fundamental process occurring in process occurring in all living organisms all living organisms to copy their DNA. to copy their DNA.

The point of DNA The point of DNA replication is to replication is to ensure that each of ensure that each of our cells contain the our cells contain the same copy of DNA same copy of DNA when the cells when the cells divide. divide.

http://www.le.ac.uk/ge/genie/vgec/images/mitosis_meiosis.png

Replication-StepsReplication-Steps

1)1) The DNA unzips (helix opens up)The DNA unzips (helix opens up)2)2) DNA polymerase (enzyme) DNA polymerase (enzyme)

starts bringing new nucleotides starts bringing new nucleotides and building two DNA moleculesand building two DNA molecules

3)3) At the end of the replication At the end of the replication procedure, there will be 2 DNA procedure, there will be 2 DNA molecules each with a parent molecules each with a parent chain and a daughter (new) chain and a daughter (new) chainchain

http://courses.cm.utexas.edu/jrobertus/ch339k/overheads-2/ch10_DNA-rep.jpg

DNA replication is DNA replication is very importantvery important

Replication Replication ensures that ensures that when our cells when our cells divide, so does divide, so does our genetic our genetic information information (DNA)(DNA)

RNA structureRNA structure

RNA RNA (ribonucleic acid)(ribonucleic acid)

The structure is like the DNA except The structure is like the DNA except that it is single stranded (1 strand as that it is single stranded (1 strand as opposed to 2 strands/chains)opposed to 2 strands/chains)

It contains 1 polynucleotide chain and It contains 1 polynucleotide chain and the nucleotides are:the nucleotides are:– Adenine (A)Adenine (A)– Uracil (U) –no Thymine in RNAUracil (U) –no Thymine in RNA– GuanineGuanine– CytosineCytosine

http://en.wikivisual.com/images/0/04/NA-comparedto-DNA_thymineAndUracilCorrected.png

Types of RNATypes of RNA

Messenger RNA (mRNA)Messenger RNA (mRNA) Transfer RNA (tRNA)Transfer RNA (tRNA) Ribosomal RNA (rRNA)Ribosomal RNA (rRNA)

The Central Dogma of The Central Dogma of BiochemistryBiochemistry

• Life depends upon the ability to Life depends upon the ability to change genetic information into change genetic information into functional proteins. functional proteins.

• This is referred to as the This is referred to as the central central dogma of biochemistrydogma of biochemistry and and consists of two processes: consists of two processes: • transcriptiontranscription• translationtranslation


DNA RNA Proteintranscription translation

in the nucleus in the cytosol





Transcription:Transcription:

The synthesis of mRNAThe synthesis of mRNA

TranscriptionTranscription

Occurs in the nucleus (in eukaryotes)Occurs in the nucleus (in eukaryotes) It is the process whereby a copy of DNA It is the process whereby a copy of DNA

(called mRNA) is made, via action of (called mRNA) is made, via action of RNA RNA polymerasepolymerase

RNA polymerase reads DNA from 5’ to 3’ endRNA polymerase reads DNA from 5’ to 3’ end The residues are pairedThe residues are paired

DNADNA RNARNAAA U U (remember no T in RNA)(remember no T in RNA)

TT AAGG CCCC GG

http://www.brooklyn.cuny.edu/bc/ahp/BioInfo/TT/TscriptD.html

5’ 3’

RNA polymerase

http://www.brooklyn.cuny.edu/bc/ahp/BioInfo/TT/TscriptD.html

5’ 3’

RNA polymerase

DNA

TranscriptionTranscription

Occurs in the nucleus (in eukaryotes)Occurs in the nucleus (in eukaryotes) It is the process whereby a copy of DNA It is the process whereby a copy of DNA

(called mRNA) is made, via action of (called mRNA) is made, via action of RNA RNA polymerasepolymerase

RNA polymerase reads DNA from 5’ to 3’ endRNA polymerase reads DNA from 5’ to 3’ end The residues are pairedThe residues are paired

DNADNA RNARNAAA U U (remember no T in RNA)(remember no T in RNA)

TT AAGG CCCC GG

Transcription (contd)Transcription (contd)

When RNA polymerase binds to When RNA polymerase binds to DNA to transcribe the DNA into DNA to transcribe the DNA into mRNA, it binds to a part of DNA mRNA, it binds to a part of DNA called the promoter region.called the promoter region.

Promoter region(where RNA polymerase binds)

Area that will be ‘read’ by RNApolymerase to create mRNA

Response element

DNA

5’ 3’

Promoter region

RNA polymerase

5’ 3’

DNA

5’ 3’

DNAmRNA

RNA polymerase

Notice how RNA polymerase reads DNA from the5’ end to the 3’ end strand.

5’ 3’

DNAmRNA

RNA polymerase

5’ 3’

mRNA

RNA polymerase

RNA polymerase dislodges from the DNA whenit reads an unusual sequence of DNA

Translation: Translation:

The synthesis of proteins from The synthesis of proteins from mRNAmRNA




TranslationTranslation

Once mRNA was synthesized (via Once mRNA was synthesized (via transcription), it leaves the nucleus of transcription), it leaves the nucleus of the cell and goes to the cytoplasm the cell and goes to the cytoplasm (aka cytosol)(aka cytosol)

In the cytoplasm, there is an In the cytoplasm, there is an organelle called the endoplasmic organelle called the endoplasmic reticulum (ER) which contains reticulum (ER) which contains ribosomesribosomes

Ribosomes facilitate protein synthesisRibosomes facilitate protein synthesis

rRNA

tRNA

amino acid

mRNA

protein

http://www.biologycorner.com/resources/translation_lettered.jpg

Translation (contd)Translation (contd)

During translation, mRNA binds to rRNA During translation, mRNA binds to rRNA (ribosomal RNA).(ribosomal RNA).

tRNA (transfer RNA) holds one amino tRNA (transfer RNA) holds one amino acid in the form of amino acyl-tRNA acid in the form of amino acyl-tRNA complexcomplex

The mRNA guides the order (sequence) The mRNA guides the order (sequence) of amino acids forming the protein of amino acids forming the protein

rRNA serves as an anvil, aligning both rRNA serves as an anvil, aligning both mRNA and tRNA so that a peptide or mRNA and tRNA so that a peptide or protein is formedprotein is formed

AUG

mRNA

CCA ACG AUA UCCAGGGAG UAG

Step 1 of TranslationStep 1 of Translation

mRNA, produced in the nucleus throughthe process of transcription, is now in thecytoplasm of the cell.

rRNA(ribosomal RNA)

AUG

mRNA



rRNA binds to the mRNA strand. It servesto hold the mRNA in place.

rRNA(ribosomal RNA)

AUG

mRNA


Step 3 of TranslationStep 3 of Translationmet

UAC

tRNA

A tRNA (transfer RNA) that matches the sequence in mRNA (AUG) arrives, carrying anamino acid. AUG codes (codon) for methionine (met)

rRNA(ribosomal RNA)

AUG

mRNA



met

The first tRNA leaves the scene.Another tRNA that matches the sequence CCA in mRNA arrives, carrying the amino acid proline (pro).

pro

GGU

rRNA(ribosomal RNA)

AUG

mRNA



met

The second tRNA leaves the scene.Met and pro form a bond (peptide bond)Another tRNA that matches the sequence ACG arrives, carrying the aminoacid threonine (thr).

pro

thr

UGC

rRNA(ribosomal RNA)

AUG

mRNA



met

The last tRNA leaves the scene.Pro and thr form a bond (peptide bond)Another tRNA that matches the sequence AUA arrives, carrying the aminoacid tyrosine (tyr).

pro thr

tyr

UAU

rRNA(ribosomal RNA)

AUG

mRNA


Final Step of Final Step of TranslationTranslation

met

UAG is a stop codon, which tells the tRNA thatno more amino acids should be incorporated.When a stop codon is reached, rRNA dissociates from mRNA and a protein is formed.

pro thr tyr ser arg glu

Stop codon

The protein that is The protein that is synthesized via synthesized via translationtranslation Can become enzymes (compounds Can become enzymes (compounds

that speed up a reaction):that speed up a reaction):– Enzymes involved in digestionEnzymes involved in digestion– Enzymes involved in metabolismEnzymes involved in metabolism

Can become muscle proteinsCan become muscle proteins Can become transport proteins that Can become transport proteins that

allow entry of certain molecules inside allow entry of certain molecules inside the cellthe cell

Can become hormones (insulin, Can become hormones (insulin, cortisol, adrenaline, etc)cortisol, adrenaline, etc)

Etc…Etc…

Amino acids and Amino acids and proteinprotein Amino acids (there are 20 of them Amino acids (there are 20 of them

in nature) are the building units of in nature) are the building units of protein.protein.

Amino acids include: Amino acids include: Alanine, Alanine, Arginine, Asparagine, Aspartic acid, Arginine, Asparagine, Aspartic acid, Cysteine, Glutamic acid, Glutamine, Cysteine, Glutamic acid, Glutamine, Glycine, Histidine, Isoleucine, Leucine, Glycine, Histidine, Isoleucine, Leucine, Lysine, Methionine, Phenylalanine, Lysine, Methionine, Phenylalanine, Proline, Serine, Threonine, Tryptophan, Proline, Serine, Threonine, Tryptophan, Tyrosine, ValineTyrosine, Valine

Codons and Codons and anticodonsanticodons

rRNA(ribosomal RNA)

AUG

mRNA



met pro thr

tyr

UAU

More about More about translation…translation… Three nucleotides (in a specific Three nucleotides (in a specific

order) code for a specific amino order) code for a specific amino acidacid

The nucleotide sequence in the The nucleotide sequence in the mRNA is called mRNA is called codoncodon

The corresponding nucleotide The corresponding nucleotide sequence in the tRNA is called the sequence in the tRNA is called the anticodonanticodon

rRNA(ribosomal RNA)

AUG

mRNA



met pro thr

tyr

UAU

codon

anticodon

rRNA

tRNA

amino acid

mRNA

protein

http://www.biologycorner.com/resources/translation_lettered.jpg

anticodon

codon

Amino Acid DNA Base Triplets mRNA Codons tRNA Anticodons

alanine CGA, CGG, CGT, CGC GCU, GCC, GCA, GCG CGA, CGG, CGU, CGC

arginine GCA, GCG, GCT, GCCTCT, TCC

CGU, CGC, CGA, CGGAGA, AGG

GCA, GCG, GCU, GCCUCU, UCC

asparagine TTA, TTG AAU, AAC UUA, UUG

aspartate CTA, CTG GAU, GAC CUA, CUG

cysteine ACA, ACG UGA, UGC ACA, ACG

glutamate CTT, CTC GAA, GAG CUU, CUC

glutamine GTT, GTC CAA, CAG GUU, GUC

isoleucine TAA, TAG, TAT AUU, AUC, AUA UAA, UAG, UAU

leucine AAT, AAC, GAA, GAGGAT, GAC

UUA, UUG, CUU, CUCCUA, CUG

AAU, AAC, GAA, GAGGAU, GAC

lysine TTT, TTC AAA, AAG UUU, UUC

methionine TAC AUG UAC

phenylalanine AAA, AAG UUU, UUC AAA, AAG

proline GGA, GGG, GGT, GGC CCU, CCC, CCA, CCG GGA, GGG, GGU, GGC

serine AGA, AGG, AGT, AGCTCA, TCG

UCU, UCC, UCA, UCGAGU, AGC

AGA, AGG, AGU, AGCUCA, UCG

stop ATG, ATT, ACT UAA, UAG, UGA AUG, AUU, ACU

http://waynesword.palomar.edu/codons.htm

The start and end The start and end codoncodon The start codon is the one that makes The start codon is the one that makes

the tRNA insert its first amino acidthe tRNA insert its first amino acid The start codon is usually AUG and The start codon is usually AUG and

codes for methioninecodes for methionine So almost all proteins begin with So almost all proteins begin with

methionine as its first amino acidmethionine as its first amino acid The stop codon is the one that makes The stop codon is the one that makes

the tRNA stop inserting amino acidsthe tRNA stop inserting amino acids UAA, UAG, UGA are all stop codonsUAA, UAG, UGA are all stop codons

Summary…Summary…

The nucleus: contains23 pairs of chromosomes.DNA is arranged in thesechromosomes.Where DNA replication and transcription occurs.

DNA replication: DNA copiesitself, every time the cell divides.Transcription: A copy ofDNA is made. This copy is called mRNA.

The ribosome: where protein is synthesized (ie translation occurs).In translation, mRNA isconverted into protein.

Cytosol or cytoplasm



replication

Replication of DNAReplication of DNA is important, since it ensures that every cell will have a is important, since it ensures that every cell will have a Copy of DNA each time the cell undergoes division.Copy of DNA each time the cell undergoes division.

Central Dogma of BiochemistryCentral Dogma of Biochemistry::Life depends upon the ability to change genetic information into functional Life depends upon the ability to change genetic information into functional proteins, via the processes known as transcription and translation.proteins, via the processes known as transcription and translation.

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Unit 1: Central Code and Genetic Material Paz Etcheverry NS 315