Chapter 1: Nucleic Acids and Proteins Flashcards
Define proteins
- Proteins are molecules made up of amino acids
Describe the difference between polypeptides and proteins
- A polypeptide is a sequence of amino acids
- One polypeptide may need to join with another to have a function and, thus, be a protein
- A protein is a sequence of amino acids with a function
Define nucleic acids
- Nucleic acids are biomolecules found in all organisms
- There are two kinds of nucleic acids: DNA and RNA
- They provide information and are involved in protein synthesis
- All have a sugar-phosphate backbone (deoxyribose/ribose)
- They are polymers made up of monomers
Define nucleotide
- Nucloetides are the basic building blocks (monomers) of DNA and RNA consisting of a phosphate group, a base and a five-carbon sugar
- Adjacent nucleotides are held together by phosphodiester bonds
Draw and label the monomers of nucleic acids
- Diagram should include
- Phosphate
- Five-carbon sugar
- Nitrogenous base
State the DNA and RNA base pairings
-
DNA
- Adenine and thymine (straight letters)
- Cytosine and guanine (curved letters)
-
RNA
- Adenine and uracil (vowels)
- Cytosine and guanine (curved letters)
Compare DNA and RNA
-
DNA
- Contains deoxyribose sugar
- Contains adenine, cytosine, guanine and thymine
- Double stranded
- Deoxyribose-phosphate backbone
-
RNA
- Contains ribose sugar
- Contains adenine, cytosine, guanine and uracil
- Single stranded
- Ribose-phosphate backbone
NOTE: The sugar in RNA contains one additional oxygen atom, compared to deoxyribose.
State the function and location of the three main forms of RNA
-
Messenger RNA (mRNA) carries genetic material in DNA from the nucleus to ribosomes
- Located in the nucleus
-
Ribosomal RNA (rRNA) work with other proteins to make ribosomes found in the cytosol
- Located in the ribosomes
- rRNA and its associated proteins create a binding site for mRNA in translation
-
Transfer RNA (tRNA) carries amino acids to ribosomes to be used for translation
- Located in the cytoplasm
- Anticodon on tRNA binds to complementary codon on mRNA
Draw and label a eukaryotic gene
- Diagram should include
- Flanking regions
- Coding region
- Upstream and downstream
- Direction of transcription
Describe the difference between introns and exons
- Introns interfere → do not provide the code for amino acids
- Exons are expressed → provide the code for amino acids
Define operator
- The operator is a region in an operon that provides a binding site for a repressor (to stop transcription)
Define gene regulation
- Gene regulation is the process of turning genes on and off
Define and provide examples of structural genes
- Structural genes are genes that code for proteins that contribute to the structure or functioning of an organism
- E.g. Keratin and collagen
Define and provide examples of regulatory genes
- Regulatory genes code for proteins that control the activity/expression of other genes (transcription factors)
- Produce factors that alter the expression of a gene
- E.g. Repressor proteins
Describe 2 ways that regulatory genes work
- Regulatory genes can work directly by producing DNA binding proteins
- These proteins bind to a region of DNA to directly turn genes on or off
- They can also work indirectly by producing signalling proteins
- These proteins trigger reactions that lead to a gene being turned on or off
Explain the importance of gene regulation
- Organisms can conserve energy and resources
- Enables organisms to adapt to changing conditions by making substances when none are available from the environment
- Allows for the expression of appropriate genes at suitable times
Draw and label a prokaryotic gene structure
- Diagram should include
- Regulatory gene
- Operon consisting of a promoter, operator, leader and structural genes
Define operon
- A cluster of structural genes in bacteria controlled by the same promoter and, thus, operates as a coordinated unit
Define tryptophan
- Tryptophan is an amino acid that is used to make proteins
- E-coli ingests it from surroundings or produces it when required
Define trp operon
- A cluster of genes in bacteria that code for the enzymes needed in the production of tryptophan
Describe the difference between repression and attenuation
-
Repression is a form of gene regulation that occurs prior to transcription
- It involves a repressor binding to the operator
-
Attenuation is a form of gene regulation that occurs during transcription
- It involves the formation of hairpin loops in the leader region
Outline the process of repression when tryptophan is present
- Tryptophan binds to the repressor protein causing changes in its shape which allows it to be active
- This allows the repressor to bind to the operator
- RNA polymerase cannot bind to the promoter and transcription does not occur
- Thus, the operon is off
NOTE: The repressor in its active form is bound to two tryptophans.
Outline the process of repression when tryptophan is absent
- The repressor is inactive and does not bind to the operator
- This allows RNA polymerase to bind to the promotor and initiate transcription
- Thus, the operon is on
Outline the process of attenuation when tryptophan is present
- The leader region is translated quickly
- This allows for the production of the termination hairpin loop
- The terminator hairpin loop causes RNA polymerase to detach from the DNA
- Transcription is stopped and the structural genes in the trp operon are not transcribed or translated
NOTE: The active tryptophan repressor that blocks RNA polymerases access to the operator and the downstream structural genes is not 100% effective. It will occasionally disconnect and allow RNA polymerase to transcribe the structural genes and therefore produce tryptophan. To overcome this, the LEADER SECTION (trp L) AND ATTENUATORS (hair pin folds) are used.