PROTEIN SYNTHESIS AND MUTATIONS

Review Questions What organelle makes proteins? Where do these organelles get their directions? What are the monomers of proteins? Can mistakes occur in the DNA? What are those mistakes called? What are the two different types of nucleic acids? What are the monomers of nucleic acids?

Protein Synthesis Protein Synthesis occurs in four steps: Transcription – DNA is re-written into mRNA mRNA is edited mRNA leaves the nucleus Translation – mRNA is read and a protein is made

What is RNA? RNA is different from DNA in 3 ways 1) The sugar in RNA is Ribose where in DNA it is Deoxyribose RNA = Ribonucleic acid 2) RNA is usually single stranded; DNA is double stranded 3) RNA includes the nucleotide Uracil INSTEAD of Thymine A – U G-C

3 types of RNA Messenger RNA (mRNA) Ribosomal RNA (rRNA) Carries the genetic code from the DNA, out of the nucleus, to the ribosomes Ribosomal RNA (rRNA) RNA found inside of the ribosomes that make up their structure Transfer RNA (tRNA) RNA that carries the amino acids into the ribosomes to make a protein

Protein Synthesis Step 1: Transcription-Copy/re-write/transcribe DNA into mRNA Step 2: Unimportant parts of mRNA (introns) get taken out of mRNA Step 3: mRNA leaves the nucleus and goes to the ribosomes Step 4: Translation- Ribosomes read the mRNA and hook on the correct amino acid

Step 1- Transcription Transcribes DNA into mRNA DNA is opened up RNA polymerase hooks onto DNA Makes complementary strand of mRNA A hooks to T U hooks to A G hooks to C

Transcribe the following DNA strand: TAGTTAGCCAGT

Step 2: Unimportant parts of mRNA are removed Introns (unimportant parts of mRNA) are removed Exons are spliced back together

Step 3: mRNA leaves the Nucleus and goes to a ribosome

Step 4: Translation Ribosomes hook onto the mRNA and read the mRNA code in groups of 3 nucleotides Codons-groups of 3 nucleotides tRNA anticodon matches up with a START codon (AUG) on the mRNA sequence and tRNA begins to bring in the correct amino acids

Amino acids hook together by peptide bonds Codons are read until a stop codon is reached

20 possible amino acids Codons code for one of 20 amino acids Proteins that are formed are based on the amino acid sequence

mRNA-AUGCUAGGCCCA Figure out the order of amino acids using the mRNA strand above

Do the whole process! DNA: T T A G C G A A T T C A mRNA: Amino Acids:

To RECAP The DNA is opened up by RNA polymerase and the DNA is transcribed into mRNA. Unimportant pieces of RNA called introns are removed from the mRNA, and the exons are spliced together. The mRNA leaves the nucleus and binds to a ribosome in the cytoplasm. The ribosome reads that mRNA code in groups of 3 called codons, and tRNA hooks on the correct amino acids that is coded for. Once a stop codon is read, the polypeptide chain is released and a new protein is formed.

Mistakes can OCCUR!!! Mistakes in the DNA are known as mutations. Not all mutations are necessarily bad, but many are detrimental (harmful) Two Types of Mutations Chromosomal mutations-large pieces of the DNA Gene mutations-Individual nucleotide errors

Chromosomal Mutations Deletion – loss of a piece of chromosome Duplication – an extra piece of an already existing piece chromosome is produced Inversion – the direction of parts of chromosome are reversed Translocation – when part of a chromosome breaks off and attaches to a different chromosome

Chromosomal Mutations

Chromosomal mutation-Nondisjuction Nondisjunction- the failure of a chromosome to separate from its homologous pair during gamete formation in meiosis.

Nondisjunction in Real Life Ex: Klinefelter’s syndrome-caused by the nondisjuction of the XX chromosomes during egg formation, causing the boy to end up with XXY

Gene Mutations Point Mutations – gene mutations involving in one or a few nucleotides. Silent Mutation Nonsense Mutation Frameshift Mutation Missense Mutation

1) Silent Mutations Single nucleotide changes in the DNA sequence. This nucleotide error, however, does not make a difference because the codon still codes for the same amino acid as it would have before.

2) Nonsense Mutations Point mutation in a DNA sequence that causes a premature stop codon. This results in an incomplete protein which usually cannot complete its function.

3) Frameshift Mutation If a nucleotide is added or deleted, the bases are still read in groups of three, but now those groupings are shifted for every codon that follows. By shifting the reading frame, frameshift mutations may change every amino acid that follows the point of the mutation.

4) Missense Mutations Mutation that occurs in an amino acid codon which results in the use of a different, but sometimes chemically similar, amino acid. The similarity between the two is enough that little or no change is often rendered in the protein structure.

Sickle Cell Anemia Sickle cell anemia is an example of a missense mutation that DOES change the protein . Substitutes A for T. Results in a defective form of the protein hemoglobin (carries oxygen in the red blood cells), causing the cells to be sickle shaped