RNA & Protein Synthesis

RNA and Protein Synthesis

• Genes are coded DNA instructions that control the production of proteins within the cell

• DNA codes for PROTEINS• Must copy part of the nucleotide sequence from

DNA into RNA (ribonucleic acid) which then helps make proteins– Proteins are made in ribosomes – need RNA to go to

ribosomes as the DNA cannot leave the nucleus

Structure of RNA

• Long chain of nucleotides– A 5-carbon sugar (ribose)– A phosphate group– And nitrogenous bases

• Differences between RNA and DNA:– Ribose (RNA) vs. deoxyribose (DNA)– RNA is single-stranded, DNA is double-stranded– RNA has Uracil (U) in place of Thymine (T)– In RNA, A bonds with U, and C bonds with G

• RNA is a disposable copy of DNA – it is a working copy of a single gene

RNA Base-Pairing Rule

A = U

G = C

Types of RNA

• Protein synthesis – assembly of amino acids into proteins controlled by RNA

• Three types of RNA– Messenger RNA (mRNA) – carry copies

of instructions for making amino acids– Ribosomal RNA (rRNA) – proteins

assembled on ribosomes– Transfer RNA (tRNA) – transfers each

amino acid to ribosome

mRNAtRNA

from to to make up

also called which functions to also called also calledwhich functions to

can be

RNA

Messenger RNA Ribosomal RNA Transfer RNA

mRNA Carry instructions rRNACombine

with proteins tRNABring

amino acids toribosome

DNA Ribosome Ribosomes

Types of RNA

Transcription: DNA RNA(pages 181-182 in book)

• Occurs in NUCLEUS for eukaryotes• RNA produced by copying part of the nucleotide sequence of DNA

into a complementary sequence in RNA = transcription (RE-WRITING DNA to RNA)

• During transcription, RNA polymerase (similar to DNA polymerase) binds to DNA and separates the DNA strands. RNA polymerase then uses one strand of DNA as a template from which nucleotides are assembled into a strand of mRNA

• RNA polymerase binds to specific regions of DNA in order to start making mRNA called promoters. The end region is called a terminator.

• In Eukaryotes, the RNA is “processed” first and then becomes mRNA which then leaves the nucleus. (ex. Introns removed since they don’t code for genes)

RNADNA

RNApolymerase

Adenine (DNA and RNA)Cystosine (DNA and RNA)Guanine(DNA and RNA)Thymine (DNA only)Uracil (RNA only)

Transcription

Transcription

The Genetic Code & Intro to Translation

(pages 179-180 in book)• Translation is taking mRNA and making proteins• Proteins become your traits!• Proteins are made by joining amino acids into long

chains called polypeptides• There are 20 different amino acids – the order of amino

acids determine what proteins will be made• “Language” of mRNA instructions is the genetic code –

codes for proteins• RNA contains four bases A, U, C, and G – where A and

U can bond together and C and G can bond together

The Genetic Code (continued)

Genetic code is read THREE letters at a time, so that each “word” of coded message is 3 bases long. Each 3 letter “word” in mRNA is called a codon which identifies a single amino acid used in a protein

Example: mRNA sequence – UCGCACGGU

Read 3 bases at a time –

UCG – CAC – GGU

Codons represent different amino acids UCG – CAC – GGU

Serine – Histadine – Glycine

What is the DNA sequence that coded for this mRNA sequence?

AGCGTGCCA

The Genetic Code (continued)

• Some amino acids can be specified by more than one codon (because there are only 20 amino acids, and 64 possible codons, some codons will overlap)

• 3 “stop” codons – signal the end of a protein• Codon AUG specifies methionine – a “start”

codon for the beginning of the protein• A chart is used to decode the codons into their

respective amino acids

The Genetic CodemRNA Sequence:

UCG

CAC

GGU

mRNA Sequence:

UCG

CAC

GGU