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Focus Question: How does DNA express phenotype? IB Topic 3.5 Transcription and Translation Overview Animation

Transcription/Translation Transcription- the making of RNA from DNA Translation- reading the RNA code to make proteins

DNA vs. RNA DNA Deoxyribonucleic Acid 2 strands- double helix Sugar Deoxyribose Bases A, C, T, G RNA Ribonucleic Acid Single strand Sugar Ribose Bases A, C, U, G

RNA strand contains a new base U = uracil Takes the place of T in DNA. An “A” in DNA will generate a complimentary “U” in RNA.

Types of RNA: rRNA: ribosomal RNA- tRNA: transfer RNA Major component of ribosomes tRNA: transfer RNA Carries amino acids to mRNA An interpreter in translation mRNA: messenger RNA Encodes genetic info from DNA and convey it to the ribosomes, where the info is translated into amino acid sequences

IB Topic 3.5- Transcription and Translation The process by which RNA is made from a DNA template Purpose: to read the DNA, one gene at a time. RNA polymerase starts transcription. Complimentary RNA strand is formed RNA is assembled in the 5’ 3’ direction Bubbles open- instead of unzipping/unwinding 2.6.2

DNA “words”… DNA gives instructions. The instructions are written in a language where words are ALWAYS three base pairs long. Ex: AAT,CCG,GCA,TTC, etc. Each is called a triplet.

Triplets on DNA make Codons on mRNA Codon- genetic code made of one triplet of bases. Codons are found on mRNA (messenger RNA)

Formation of mRNA Creates a “mirror image” of the triplets found on DNA (except TU) mRNA then travels out of the nucleus and toward a ribosome. This is called transcription

New Enzyme- RNA Polymerase Links together the growing chain of RNA nucleotides during transcription Uses DNA as template Similar to DNA polymerase but only facilitates a reaction on one side of the strand Animation

Once at the ribosome Translation starts

Steps of Translation mRNA codons get “read” by the ribosome. tRNA brings matching anticodon to codon. Amino acid associated with that tRNA drops onto polypeptide chain AUG is the start codon

CodonAmino Acid Use a codon chart to determine which AA’s are being made Example:

Polypeptide Polypeptide- a string of amino acids. Ex: leu-cys-ser-tryp-leu Intro to translation

Why make proteins? Proteins make up most tissue in your body – skin, all organs, muscles, etc. Proteins make you who you are.

Protein synthesis = Translation Ribosomes- synthesize protein (polypeptide chains) in a process called Translation.

The Code is Degenerate Degenerate- each amino acid can by synthesized by more than one codon. Ex: both UUU and UUC make phenylalanine

The code is universal The same codons are found in all living organisms.

What section of DNA makes one polypeptide? One gene  one polypeptide A “gene” is defined as such because it contains the code for making ONE polypeptide. Each polypeptide can draw its origins back to ONE gene. One gene one polypeptide hypothesis

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