Use the image above to answer these questions. 1. Does the process shown above use ATP? 2. The process shown above moves molecules [up, down] the concentration gradient. 3. A molecule of glucose would use which protein to enter the cell? B A

 Recall that DNA is used to create new proteins and determine your physical characteristics.  The Genetic Code determines the exact proteins that will be created.

 Creating new proteins is a three step process: › First, DNA is transcribed within the nucleus. This process forms RNA. › Second, the RNA is exported from the nucleus to the cytoplasm. › Third, the RNA attached to ribosomes, and is translated to create a chain of amino acids – also known as a protein!

 Transcription is the process of creating a strand of RNA that is complimentary to a given strand of DNA.  The RNA is designed to be a temporary copy, and will be quickly chewed by enzymes in the cytoplasm.  Think of DNA as a master copy, and RNA as the photocopies!

 RNA stands for ribonucleic acid.  RNA is unique in that it is (usually!) single stranded.  Also, RNA has four bases, but they are slightly different from those of DNA.

Similarities Differences  Both are types of nucleic acid.  Both are composed of nucleotides.  Both have four nitrogen bases.  DNA is double-stranded, RNA is single- stranded.  DNA has the bases A, C, G and T. RNA has the bases A, C, G and U. › The U stands for uracil. It takes the place of thymine in RNA, and base pairs with adenine.  DNA is permanent, and RNA is temporary.

 Transcription is the process of making a complimentary strand of RNA.  You WILL need to use base pairing rules on some questions. Remember, RNA does NOT have thymine! If the DNA base is……then the correct RNA base is… A (adenine)U (uracil) C (cytosine)G (guanine) C (cytosine) T (thymine)A (adenine)

1. Double-stranded DNA opens up, forming a replication bubble. 2. RNA polymerase binds to promoters sequences, and begins to transcribe the DNA into messenger RNA (mRNA). 3. The polymerase detaches at a stop sequence, and the mRNA breaks away. 4. The mRNA strand is processed (in eukaryotes!) and moves to the cytoplasm.

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 Often, the mRNA produced in transcription needs to be processed further. In eukaryotes, we add a 5’ cap and a 3’ poly-A tail.  Sometimes, we also need to remove sequences from the mRNA. › Sequences REMOVED: introns › Sequences KEPT: exons

1. Put these steps of transcription in order: a. mRNA detaches from DNA b. mRNA is created through base-pairing c. mRNA is modified and exported. d. DNA unwinds, and polymerase attaches 2. Base pair the correct sequence of RNA with this sequence of DNA: CTAAGATCGATC

 In translation, the mRNA we produced in transcription will be used to make a protein.  But, how do we know what proteins will be made?

 The cell groups each sequence of three nucleotides as a codon.  Each codon matches up with an amino acid. This is how we create proteins!

 Why three nucleotides in a codon?  We need to be able to code for all twenty amino acids. Using probability, sequences of three letters are the shortest that can code for all twenty. › One base: 4 possibilities (A, C, G, U) › Two bases: 16 possibilities (4x4) › Three bases: 64 possibilities (4x4x4)

 However, we now have a new problem: we have too many sequences for all twenty amino acids!  As a result, many amino acids are represented by multiple sequences. For instance, alanine has four sequences, and arginine has six! › Note: the third letter of a codon is the LEAST important. We’ll come back to this later.

 The steps of translation: 1. A ribosome is constructed at a start codon. This will ALWAYS be AUG! 2. A transfer RNA (tRNA) binds to the codon, and drops off the appropriate amino acid. 3. This process repeats until the ribosomes hits a stop sequence. This will be the first instance of either UAA, UAG or UGA.

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Use this sequence for these questions: TGCAGCAATGAC 1. Transcribe this sequence to mRNA. 2. Translate the mRNA sequence you made to a sequence of amino acids. 3. How many ATP molecules are made by a bacteria in cellular respiration? Is this an example of aerobic or anaerobic respiration?

 A gene is a portion of the DNA that is used to code for protein. Genes are quite rare; only about 1% of the DNA in your cells is used to make protein!  Genes are regulated, such that they are NOT making protein all of the time. Cells only want to activate genes when needed.  Genes can be repressible or inducible.

 A repressible gene is USUALLY ACTIVE, but can be shut down by a repressor.  The catch is, the repressor is only active in the presence of molecules created by the gene’s enzyme!  This way, the gene turns off after it has been used enough times.

 An inducible gene is USUALLY INACTIVE, but can be activated by an inducer.  The catch is, the inducer that removes the repressor is the substrate for the enzyme for this gene!  This way, the gene turns is only on when the enzymes can be used.