RNA and Protein Synthesis

Chapter 13 (M)

Information Flow Language of DNA is written as a

sequence of bases If the bases are the letters the

genes are the sentences Information in DNA is made into

Protein RNA carries & translates the

message in DNA to protein DNA RNA Protein

Flow of information:

The “Central Dogma”

proteinRNADNAtranscription translation

replication

How do we move information from DNA to proteins?

Types of Nucleic Acid DNA (Deoxyribonucleic

Acid) - transmits genetic information that is passed from one generation to the next-double helix

RNA (Ribonucleic Acid)

Nucleotide

Composed ofa nitrogen

base a pentose

sugara phosphate

group

Structure of DNA & RNA

DNA double strands

(a) 5 carbon sugar - deoxyribose

(b) phosphate group

(c) nitrogenous base – adenine (A), guanine (G), thymine (T), cytosine (C)

A=T, G=C

RNA single strand (a) 5 carbon sugar -

ribose (b) phosphate

group (c) nitrogenous

bases - adenine (A), guanine (G), uracil (U),cytosine (C)

A=U, G=C

RNA-Ribonucleic Acid Single stranded Ribose sugar Four bases

Adenine, Guanine, Cytosine & Uracil(U)

Uracil similar to Thymine and pairs with Adenine

Types of RNA

1. m RNA transfers the genetic code of DNA in the nucleus to the ribosome in the cytoplasm

2. t-RNA transfers amino acids to the ribosome to make proteins

3. r- RNA ribosomal RNA

Transcription: DNA RNA

Construction of RNA along portions of the DNA molecule

Stages InitiationElongationTermination

Initiation DNA is double stranded and has

regions on it “Promoters” (TATA box) where transcription starts.

1. DNA is unzipped, bases are exposed2. “RNA Polymerase” attaches to the

promoter region ready to start making RNA

Elongation1. RNA nucleotides pair with the

exposed DNA bases2. RNA Polymerase then links the RNA

nucleotides together to form a chain (mRNA)

3. As the RNA peels off the DNA chain, DNA strands rejoins.

Termination When the RNA Polymerase reaches a

special base sequence of DNA (terminator) which signals the end, the RNA Polymerase detaches from the DNA

Two other types of RNA – tRNA & rRNA are made in the same way

Editing the RNA Message RNA transcribed in the nucleus is

modified before it leaves the nucleus as mRNA to be translated.

mRNA Introns noncoding regionsExons the parts that remain & will be

translated, or "expressed RNA Splicing joining of the exons

after the introns are removed

RNA Splicing

Ribosomes and Protein Synthesis

13.2

The Triplet CodeDNA stores information to make

protein 20 AAs, functional if order is correct

English 1000s words arrangement of 26 letters

DNA Code sequence of 3 bases (A,T,G,C) genetic alphabet

Start Codon = 1, Stop Codons =3

The Triplet Code

Translation Process by which mRNA code is

read and converted into a specific amino acid sequence (protein)

Players:1. Ribosomes2. mRNA3. tRNA

Ribosomes Made of two subunits

Large p-site,& A-siteSmall m RNA binding site

t-RNA

Steps in Translation

1. Initiation2. Elongation 3. Termination

Initiation mRNA binds to small subunit of

ribosome

Initiator tRNA binds to specific start codon on mRNA & carries the AA MetAnticodon=UAC(tRNA)Codon =AUG (mRNA)

Large subunit binds to the small functional ribosome

Initiation

Initiation

Elongation Codon Recognition: incoming tRNA

with an AA attached pairs with the mRNA codon on the “A-site”

Peptide bond formation: a bond is formed between the AA or peptide on “P-site” & AA on the “A-site”

Translocation: “P-site” tRNA moves out. “A-site” tRNA w/polypeptide chain moves to “P-site”

Ribosome with mRNA and tRNA

Figure 17.18 The elongation cycle of translation

Termination

Process continues till a “stop codon” is reached

Process is terminated. Stop Codons: UAA, UAG, UGA

Termination

Mutations in Genes

Ch 13.3

Mutation A change in the nucleotide sequence

of DNA Can involve large sections of the DNA

or just a single nucleotide pair (Point mutations)

TypesBase SubstitutionBase DeletionBase Insertion

Base Substitution

Base Substitution

Base Insertion/Deletion

Is usually more disastrous than the effects of base substitutions

RNA is read as a series of triplets, thus adding or removing nucleotides will affect all nucleotides downstream.

Will result in a different , non working protein

Causes of Mutations May occur when errors are made

during DNA replication When errors are made during

chromosome crossovers in meiosis.

Physical or chemical agents mutagens

Mutagen

Physical mutagen high-energy radiation X-rays and ultraviolet light.

Chemical mutagen chemicals that are similar to normal DNA bases but cause incorrect base-pairing when incorporated into DNA.

Mutations: Good or Bad

Harmful Cancers Sickle cell disease

Beneficial Chemical

resistance Plants polyploidy

Mutations: Good or Bad Mutations genetic

diversity May be beneficial

tiger swallowtail butterfly mutations cause a change in color predators confuse it with w/ black swallowtail which is poisonous and avoid it