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Human Genetics. Translation of RNA into Protein. Replication. DNA. Transcription. RNA. Nucleus. Translation. Protein. . Cytoplasm. Central Dogma. Human Genome. 3.2 million DNA base pairs 1.5\% encode proteins < = > 98.5\% not protein encoding

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human genetics

Human Genetics

Translation of RNA into Protein

central dogma
Replication

DNA

Transcription

RNA

Nucleus

Translation

Protein

.

Cytoplasm

Central Dogma
human genome
Human Genome

3.2 million DNA base pairs

1.5% encode proteins < = > 98.5% not protein encoding

~ 31,000 genes encoding 100,000 - 200,000 proteins

How are 100,000 to 200,000 proteins produced from 31,000 genes?

What is the 98.5% of the human genome that does not encode proteins?

two types of nucleic acids
RNA

Usually single-stranded

Has uracil as a base

Ribose as the sugar

Carries protein-encoding information

Can be catalytic

DNA

Usually double-stranded

Has thymine as a base

Deoxyribose as the sugar

Carries RNA-encoding information

Not catalytic

Two types of nucleic acids
slide6
# of strands

kind of sugar

bases used

rna structure depends on sequence
RNA Structure Depends on Sequence
  • A can pair with U and the C with G via hydrogen bonding just as with DNA.
  • Secondary RNA structure is critical in how it performs its function.
  • RNA Structure and RNA Sequence enable an RNA to interact specifically with proteins.
rna processing
RNA Processing

mRNA transcripts are modified before use as a template for translation:

  • - Addition of capping nucleotide at the 5’ end
  • - Addition of polyA tail to 3’ end
  • Important for moving transcript out of nucleus
  • And for regulating when translation occurs

Splicing - the removing internal sequences

- introns are sequences removed

- exons are sequences remaining

protein structure was solved before dna was known to be genetic material

Protein Structure was solved before DNA was known to be genetic material

Linus Pauling and Alpha Helix led to model building by Watson and Crick

proteins
Proteins
  • most abundant type of molecules in cells
  • responsible for most biological functions
  • muscle contraction - myosin and actin
  • oxygen transport - hemoglobin
  • immune system -antibodies
  • connective tissue - cartilage
  • hair/skin - keratin
  • metabolism - enzymes
protein basics
Protein Basics
  • Proteins are polymers assembled from amino acids
  • 20 different amino acids are used
  • Bond between amino acids is called the "Peptide Bond".
  • Peptide Bond is formed between the carboxyl group of one amino acid and the Alpha amino group of another amino acid.
  • mRNAs have a 5' end and a 3' end - they have Polarity.
  • Proteins also have polarity.
protein folding is critical
Protein Folding is Critical
  • How is protein folding directed within cells?
  • This is still an active area of research, but to a large degree, protein sequence determines protein folding.
protein polarity
Protein Polarity
  • The Amino acid at one end of a protein chain has a free Alpha amino group.
  • Called "Amino-Terminus" or "N-terminus" of the protein.
  • Amino acid at other end has a free Alpha carboxyl group.
  • Called "Carboxy-Terminus" or "C-terminus" of the protein.
  • Direction of Protein Synthesis is from N-terminus to C-terminus.
the genetic code
The Genetic Code
  • There is a 3 to 1 correspondence between RNA nucleotides and amino acids.
  • The three nucleotides used to encode one amino acid are called a codon.
  • The genetic code refers to whichcodons encode which amino acids.
  • How do we know it is a 3 letter code?
how do the mrna nucleotides direct formation of the amino acids in a protein
Codons of one nucleotide:

A

G

C

U

Codons of two nucleotides:

AA GA CA UA

AG GG CG UG

AC GC CC UC

AU GU CU UU

Can only encode

4 amino acids

Can only encode

16 amino acids

How Do the mRNA Nucleotides Direct Formation of the Amino Acids in a Protein?

Proteins are formed from 20 amino acids in humans.

slide22
Codons of three nucleotides:

AAA AGA ACA AUA AAG AGG ACG AUG

AAC AGC ACC AUC AAU AGU ACU AUU

GAA GGA GCA GUA GAG GGG GCG GUG

GAC GGC GCC GUC GAU GGU GCU GUU

CAA CGA CCA CUA CAG CGG CCG CUG

CAC CGC CCC CUC CAU CGU CCU CUU

UAA UGA UCA UUA UAG UGG UCG UUG

UAC UGC UCC UUC UAU UGU UCU UUU

Allows for 64 potential codons => sufficient!

slide25
DNA

template

strand

DNA

C

A

G

C

A

G

T

T

T

Transcription

A

A

G

U

C

A

G

U

C

Messenger

RNA

mRNA

Codon

Codon

Codon

Translation

Polypeptide

(amino acid

sequence)

Protein

Lysine

Serine

Valine

Translation

  • The process of reading the RNA sequence of an mRNA and creating the amino acid sequence of a protein is called translation.
universal code
Universal Code?
  • In some organisms, a few of the 64 possible "words" of the genetic code are different.
  • Do a few different words mean that the code is not universal?
  • Perhaps: if you're willing to say that the US and Britain don't share a common language because elevators in the UK are called "lifts" and they spell the word "color" with a "u.“
the genetic code is
The Genetic Code Is
  • Linear: uses mRNA which is complementary to DNA sequence.
  • Triplet: the unit of information is the codon, a series of three ribonucleotides.
  • Unambiguous: each codon specifies only one amino acid (AA).
  • Degenerate: more than one codon exists for most amino acids.
the genetic code is32
The Genetic Code Is:
  • Punctuated: there are codons that indicate “start” and “stop.”
  • Commaless: there is no punctuation within a mRNA sequence.
  • Nonoverlapping: any one ribonucleotide is part of only one codon (some exceptions exist).
  • Universal: the same code is used by viruses, bacteria, archaea, and eukaryotes.
point mutations
Point Mutations
  • Single Base Change can alter protein product.
  • Misssense: results in one amino acid change.
  • Nonsense: results in stop codon.
  • Frame-shift: change "reading-frame" of genetic message.
  • Silent mutations: point mutations that DON’T alter the protein product because of the degenerate nature of the genetic code.
frame shift
Frame Shift
  • Within a gene, small deletions or insertions of a number of bases not divisible by 3 will result in a frame shift. For example, given the coding sequence:

AGA UCG ACG UUA AGC

  • corresponding to the protein

arginine - serine - threonine - leucine - serine

frame shift35
Frame Shift
  • The insertion of a C-G base pair between bases 6 and 7 would result in the following new code, which would result in a non-functional protein. Every amino acid after the insertion will be wrong.

AGA UCG CAC GUU AAG C

Corresponding to the protein:

arginine - serine - histidine - valine – lysine

  • The frame shift could generate a stop codon which would prematurely end the protein.
how to recognize protein information in dna
How to Recognize Protein Information in DNA
  • Don't assume that a dsDNA molecule will be read from left to right on the top strand.
  • Every dsDNA sequence has six possible translations:
  • top / bottom strand each with a 1st / 2nd / 3rd reading frame
  • Not every AUG or "stop" sequence is a start or stop codon.
  • ORF is the Open Reading Frame- It has an ATG in frame with a Stop codon. It could encode a protein.
comma free and non overlapping are correct
Comma free and non-overlapping are correct.
  • The living cell does decodes the messenger RNAs by a kind of dead-reckoning.
  • Ribosomes march along the messenger RNA in strides of three bases, translating as they go.
  • Except for signals that mark where the ribosome is supposed to start, there is nothing in the code itself to enforce the correct reading frame.
  • Three codons serve as stop signs: UAA, UAG or UGA
what reading frame should be used
What reading frame should be used?
  • In any mRNA sequence, there are three ways triplet codons can be read.
  • Each way to read the codons is called a "Reading Frame".
  • It is very important for ribosome to find correct reading frame.
  • If the wrong reading frame is used, translation generates a protein with the wrong amino acid sequence which is not functional.
at what codon in the mrna does the ribosome begin translation
At what codon in the mRNA does the ribosome begin translation?
  • Recall there is a 5’ untranslated region of the messenger RNA.
  • The solution is that the ribosome begins translation at a specific AUG codon within the mRNA template termed the "Start Codon".
  • This is a methionine codon, so the first amino acid in proteins is almost always methionine.
translation has three steps
Translation has Three Steps

Initiation - translation begins at start codon (AUG=methionine)

Elongation - the ribosome uses the tRNA anticodon to match codons to amino acids and adds those amino acids to the growing peptide chain

Termination - translation ends at the stop codon

UAA, UAG or UGA

translation initiation42
Leader

sequence

Small ribosomal subunit

5’

3’

U

U

C

G

U

C

A

U

G

G

G

A

U

G

U

A

A

G

C

G

A

A

mRNA

mRNA

U

A

C

Met

Initiator tRNA

Translation Initiation

Assembling to

begin translation

translation initiation43
A

U

G

G

G

A

U

G

U

A

A

G

C

G

A

5’

3’

mRNA

U

A

C

C

C

U

tRNA

Aminoacid

Gly

Met

Largeribosomalsubunit

Translation Initiation

Ribosome

translation elongation
A

U

G

G

G

A

U

G

U

A

A

G

C

G

A

5’

3’

mRNA

U

A

C

C

C

U

Gly

Met

A

C

A

Cys

Translation Elongation
translation elongation45
A

U

G

G

G

A

U

G

U

A

A

G

C

G

A

A

C

A

5’

3’

mRNA

C

C

U

Gly

C

Met

A

U

Cys

Translation Elongation
translation elongation46
A

U

G

G

G

A

U

G

U

A

A

G

C

G

A

A

C

A

U

U

C

5’

3’

mRNA

C

C

U

Gly

Met

C

A

U

Cys

Lys

Translation Elongation
translation elongation47
A

U

G

G

G

A

U

G

U

A

A

G

C

G

A

A

C

A

5’

3’

mRNA

U

C

U

Cys

U

C

C

Lys

Gly

Lengthening

polypeptide

(amino acid chain)

Met

Translation Elongation
translation elongation48
A

U

G

G

G

A

U

G

U

A

A

G

C

G

A

A

C

A

5’

3’

mRNA

U

C

U

U

Cys

G

C

C

U

C

Lys

Gly

Arg

Met

Translation Elongation
translation elongation49
A

U

G

G

G

A

U

G

U

A

A

G

C

G

A

A

C

A

5’

3’

mRNA

U

C

U

U

Cys

G

C

C

U

C

Lys

Gly

Arg

Met

Translation Elongation
translation termination
A

U

G

G

G

A

U

G

U

A

A

G

C

G

A

Stop codon

5’

mRNA

U

A

A

G

C

U

Cys

A

C

A

Arg

U

C

U

Lys

Gly

Met

Translation Termination

Release

factor

translation termination51
A

U

G

G

G

A

U

G

U

A

A

G

C

G

A

Stop codon

5’

mRNA

U

A

A

G

C

U

U

C

U

Release

factor

Arg

Lys

Gly

Met

Cys

Translation Termination

Ribosome reaches stop codon

translation termination52
G

A

G

A

G

U

A

C

A

U

G

G

U

G

A

A

A

U

G

C

U

Arg

Lys

Cys

Gly

Met

Translation Termination

Once stop codon is reached,

elements disassemble.

Release

factor

slide55
5'- G T A A T C C T C -3'DNA sense (partner) strand

3’- C A T T A G G A G -5’DNA template (antisense) strand

5'- GUA AUC CUC -3'mRNA

N - val - ile - leu - Cprotein

By convention, amino acid sequences are written and numbered left-to-right from N-terminus to C-terminus.

slide62
5'-AUG-3'codon in mRNA|||3'-UAC-5'anticodon in tRNA

5'-CAU-3'if anticodon is written 5’->3'

rna splicing depends on sequence and structure
RNA Splicing Depends on Sequence and Structure

http://bcs.whfreeman.com/thelifewire/content/chp14/1402001.html

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