BIOLOGY 12

Protein Synthesis

Epigenetics

our lifestyles and environment can change the way our genes are expressed

do identical twins have the exact same DNA?

Twins Video http://www.youtube.com/watch?v=avWwfuJYnnI

What do you know about RNA?

single stranded. uracil instead of thymine 3 types – mRNA, rRNA, tRNA can go through nucleus into cytoplasm

What do you know about Proteins?

polypeptides, long chains of amino acids amino group, carboxyl group, peptide bonds made in ribosomes used for structure – hair, muscles, nails,

feathers, wool, hormones

Gene

a sequence of nucleotides in DNA that provides the instructions to build a particular polypeptide

note: one gene codes for one polypeptide

Codons

sequence of three bases in DNA or mRNA that code for a particular amino acid

triplet of nucleotides more than one codon can code for a single

amino acid

examples: CAA or GCU

Amino acid Abbreviation

Alanine Ala

Arginine Arg

Asparagine Asn

Aspartic acid Asp

Cysteine Cys

Glutamic acid Glu

Glutamine Gln

Glycine Gly

Histidine His

Isoleucine Ile

Leucine Leu

Lysine Lys

Methionine Met

Phenylalanine Phe

Proline Pro

Serine Ser

Threonine Thr

Tryptophan Trp

Tyrosine Tyr

Valine Val

Codons

note: AUG is most often used as the start codon

see table page 240

* remember: DNA never leaves the nucleus

RNA is used as a messenger and a transporter

Three Types of RNA

mRNA: messenger RNA

delivers instructions to build a protein to the ribosome

rRNA: ribosomal RNA

structural component of a ribosome tRNA: transfer RNA

transports appropriate amino acids to ribosome

Stage 1: Transcription

DNA is used as a template to make a complementary mRNA

mRNA transcribes the message from a gene and delivers it to the ribosome

DNA mRNA

Stage 1: Transcription

Initiation

DNA uncoils at the site of a gene one strand will act as a template

Stage 1: Transcription

Elongation

RNA polymerase attaches to the DNA RNA nucleotides match up to the DNA

template forming mRNA base pair rules: A-U and C-G

Stage 1: Transcription

Termination

mRNA is released

Stage 1: Transcription

Posttranscriptional Modification

5’ cap added to start of mRNA, for protection from digestion

poly-A tail is a string of adenine bases at the end of mRNA

then mRNA leaves nucleus through nuclear pores

Stage 1: Transcription

Stage 2: Translation

a ribosome assembles amino acids in a specific sequence

mRNA is transcribed into a polypeptide

mRNA protein

Stage 2: Translation

two subunits of a ribosome bind to the mRNA the ribosome moves along the mRNA in the 5’ to

3’ direction, three nucleotides at a time this is the reading frame

Stage 2: Translation

the ribosome recognizes the start codon (AUG)

new amino acids are added each time the ribosome reads a new codon

Stage 2: Translation

tRNA delivers the amino acids it’s anti-codon recognizes the codons in the

mRNA each tRNA arrives at the A site (acceptor) the next tRNA arrives at the A site and the tRNA

prior to that shifts to the P site (peptide) this is where peptide bonds are formed between

adjoining amino acids

Stage 2: Translation

the ribosome then shifts (translocates) to the next codon

the process will continue until the ribosome reaches a stop codon

Stage 2: Translation

A site

P site

Protein Synthesis

Protein Synthesis

Wisc-Online Animation

http://www.wisc-online.com/objects/ViewObject.aspx?ID=ap1302

Protein Synthesis Example

what makes a firefly glow? Learn Genetics

http://learn.genetics.utah.edu/content/begin/dna/firefly/fireflymon8.swf

Protein Synthesis

Transcribe and Translate

http://learn.genetics.utah.edu/content/begin/dna/transcribe/

Textbook Review

protein synthesis

Read: pages 237-244pages 250-253

Questions: page 241 # 1, 4, 5, 6, 9, 10, 11

page 254 # 3, 9