Protein SynthesisHow DNA Works

LT’s 1-5

Recall…• Chromosomes are inherited from both parents

in their gametes at the time of fertilization. • This give you your full set of chromosomes or

diploid number. • You now have two sets of chromosomes, on

which are all the genes for all your traits.

!! 46 chromosomes, 23 homologous pairs, 34,500 genes from 3 trillion

nitrogen bases!!

23 pairs!

34,500!

3 trillion base pairs

So what if something goes wrong?

• With the number of chromosomes?– Not 46 total?– Monosomy or Trisomy

• With the contents of the chromosomes? – All 46 chromosomes are present– Part of a chromosome is in error?– Gene(s) do not function properly?

Meiosis Issue

DNA Issue

What DNA IsRecall that DNA is…• A long stringy molecule located in the nucleus of

eukaryotic cells (or the cytoplasm of prokarytic cells)

• It is made up of two complimentary strands bonded together by hydrogen bonds

• The overall shape is a double helix (twisted ladder) discovered by Watson and Crick

• The base unit is a nucleotide. Each nucleotide is made up of a deoxyribose sugar, a phosphate and a nitrogen base.

• There are four nitrogen bases (A, T, C and G)

LT 1

How DNA is CopiedReplication is the process by which the DNA molecule is

copied• The molecule is unzipped and the parent strands act as

templates for creating new strands (recall…free nucleotides, helicase and DNA polymerase)

• At the end of replication, two new molecules are formed– They are ½ the parent strand and ½ new– They are identical to the original molecule.

• One copy of each molecule goes to each new daughter cell

• It is a double helix• It can be copied and passed on• But this does not tell us how it actually works!

Genes- segments of DNA/chromosomes that code for a particular set of instructions, specifically the production of PROTEINS!

Coding DNA = 1.5% of the total DNA molecule• Therefore only 1.5% of DNA actually makes proteins• This 1.5% accounts for 21,000 genes and make the +100,000

proteins we have

How DNA Works

How DNA Works• Proteins are chains called polypeptides that

do any number of jobs within the cell• Proteins made up of smaller molecules called

amino acids• Amino acids are units made according to the

instructions of DNA

How DNA Works• There are 20 amino acids found in nature

– 10 we can make in our bodies– 10 are taken in from our foods

• The 20 amino acids are made from the nitrogen bases of DNA (A, T, G, and C)

• The nitrogen bases are the “alphabet” of DNA– 4 letters only in the alphabet– Each “word” created by the alphabet is only 3 letters long– Each 3-letter word is called a CODON and – Each codon represents an AMINO ACID

How DNA WorksExample:

A T E = ate, eat, tea(the letters are the same but the words are different and have different meaning)

• Same goes with nitrogen bases A, T, C and G, the order will determine the meaning and the kind of amino acid.

• Some codons form amino acids and some act like punctuation. • Those that are punctuation cut the amino acid chain and form the protein• Changes in the order and number of the amino acids can give any number or proteins.

DNA Codon

Amino Acid

ATC Stop

ACT Stop

TAC Start

TCA Serine

CAT Valine

CTA aspartate

RNARNA- a kind of nucleic acid; made up of a ribose sugar, a phosphate group and a nitrogen base (AUGC)•used to make proteins by assembling amino acids outside of the nucleus

LT 2

DNA v. RNADescripti

onMaster

molecule that stays in the nucleus

Blueprint that can leave the

nucleus

Sugar Deoxyribose Ribose

# of strands

2 strands 1 strand

Nitrogen Bases

A, T, C and G A, U, C and G

Jobs Master molecule that gives

instructions for making proteins

Molecules that follow the

directions of DNA to make

proteins

RNA3 Types of RNA1. Messenger RNA (mRNA)-is a copy of the DNA

instructions to assemble amino acids2. Ribosomal RNA (rRNA)-part of the ribosome

where proteins will be made; most abundant kind of RNA

3. Transfer RNA (tRNA)-transfers/brings each amino acid to mRNA according to the mRNA codons

RNARibosome is the organelle where…• mRNA travels to from the nucleus to make proteins. • Also where the tRNA brings each amino acid

• Made of rRNA and proteins• Two parts; large and small subunits• Made by the nucleolus• Found on the rough ER and in the cytoplasm• Involved in protein production (protein factories)

Protein SynthesisProtein Synthesis – the process by which proteins

are made from DNA with the help of RNA. There are 2 processes called transcription and translation

Transcription

Translation

Protein Synthesis

Transcription

When DNA is copied into RNA this is called transcription

LT 3

TranscriptionTranscription is helped by an enzyme called RNA Polymerase

– binds to DNA at the promoter (a specific sequence of DNA where RNA polymerase knows to bind to start copying DNA-uses transcription factors and a sequence of bases called the “TATA” box to find this region)

– Separates DNA strands for transcribing– Needs to transcribe just one strand of DNA

as its template called the template strand– Can read 60 nucleotides at time– Multiple RNA Polymerases can work at one

time to make large amounts of protein– When transcription is done, a strand of

mRNA is made

Transcription• This process occurs in the nucleus• When DNA is copied by mRNA the base

pairing is as follows…DNA A T G C A C C

mRNA U A C G U G GLet’s Watch This

Transcription• Before the mRNA can leave the nucleus, the

ends are protected by adding – A 5’ cap to the 5’ end AND– A poly-A group to the 3’ end– These protect the mRNA so it doesn’t degrade.– Think aglets on shoelaces– The 5’ cap and Poly-A ends are not read and do not give amino acids

Human Genome Project

Coding DNA = 1.5% of the total DNA molecule

• DNA is discontinuous meaning the Coding DNA is mixed in with the Non-Coding DNA;

• Coding “chunks” are called EXONS

• Non-coding DNA “chunks are called INTRONS

• And the exons can be arranged in various configurations so we get the +100,000 proteins – ALTERNATIVE SPLICING

RECALL

Introns-spliced out!

This is called the PRIMARY

TRANSCRIPT and never leaves the

nucleus

This is called the FINAL TRANSCRIPT

and leaves the nucleus for translation

Discontinuous!

Continuous!

This is done by the snRNP’s (small

nuclear ribonuclear proteins) or the

SPLICOSOME

Watch this!

TranslationLT 4

Protein Synthesis Transcription Translation PROTEIN

TranslationTranslation – the 2nd step in protein synthesis; when the

mRNA is translated/read by tRNA to make the protein

• Takes place at the ribosome in the cytoplasm• tRNA brings the appropriate amino acids to mRNA

based on the mRNA codons• tRNA is amino acid specific; in other words there is

one tRNA for each codon and it brings only one kind of amino acid

Translation• tRNA translates mRNA by matching its own

bases to those on mRNAanti-codon- the 3 base pairs on

tRNA that pair with mRNA and tell tRNA which amino acid to bring

Translation• As the amino acids are brought together by the tRNA’s they are bonded together by peptide bonds

• At the stop codon of mRNA, no more amino acids are brought and the protein is complete.

LT 3 & 4

MutationsMost of the time, DNA replication and protein synthesis

take place without error, but mistakes do happen

Mutation – any change in the genetic material; mistakes made when copying DNA.

2 Kinds of Mutations:1. Gene mutation - change in the gene

2. Chromosomal mutation - change in the chromosome

LT 5

MutationsGene Mutations – a change in 1 or a few nucleotide

bases

1. Point Mutation-change in one nitrogen base– Usually only affects one amino acid, but can change the function of the

whole protein– Substitution-one base is switched with another

EX: THE DOG BIT THE CATTHE DOG BIT THE CAR

Ex: Sickle Cell Anemia

Mutations2. Frameshift Mutation- one base is missing or

added into the DNA sequence– Affects every amino acid after the mutation– Insertion – adding one base to the sequence– Deletion – loss of one base from the sequence – Ex: Tay Sachs and Crohn’s Disease

MutationsChromosomal Mutations-

changes in the chromosome 4 Kinds of Chromosomal

Mutations:1. Deletion –loss of all or part

of the DNA EX: Inflammatory Disease

2. Duplication – extra parts of the chromosome are present

EX: Bar duplication in Fruit Flies

Mutations3. Inversion – part of a

chromosome gets flipped in the reverse direction of its usual direction

EX: Kinds of cancers

4. Translocation – when part of one chromosome breaks off and attaches to another, different chromosome

Ex: Ewing’s Sarcoma

KaryotypesA karyotype is an organized arrangement of in

individual’s chromosomes. • Chromosomes are arranged by number and size• Geneticists also look for banding patterns (the genes) and where the centromere lies. • Differences from a normal karyotype let

geneticists know if a disorder exists.

KaryotypesNormal Male

Normal Female

Karyotypes and Genetic Disorders

Geneticists can use karyotypes to find genetic disorders.

Trisomy Monosomy Deletion

LOOK AT ME FOR YOUR PROJECT!!

MutationsCauses:– Random, spontaneous mutations (errors in cell

division or DNA replication)OR– Environmental Factors (radiation, chemicals, etc)

MutationsSignificance of Mutations:1. Harmless-the change in the gene creates variation within the species

but does not harm the individual having it. EX: different coat colors in mice

2. Harmful-the change in the gene or chromosome changes the way the organism should function

EX: Cystic Fibrosis (gene) or Down Syndrome (chromosome)

3. Beneficial-creates a variation that helps an organism survive better than other members of the species

EX: HIV-1 mutation (these people do not get HIV as easily b/c they can break down a protein in HIV)