Chapter 12/15 Flashcards
(16 cards)
Contrast DNA and RNA
DNA:
-Function: Store genetic information
-Sugar Present: Deoxyribose
-Bases Present: Adenine (A), Thymine (T), Cytosine (C), Guanine (G)
-Double-stranded
RNA:
-Function: Helps in protein synthesis; acts as a messenger, builder, and translator
-Sugar Present: Ribose
-Bases Present: Adenine (A), Uracil (U), Cytosine (C), Guanine (G)
-Single-stranded
Look back at your Chapter 3 study guide to explain how the primary structure
of a polypeptide is determined.
Amino acid sequence
Determined by genetic material
Define Gene Expression and summarize the purpose of the two major processes involved. Transcription and Translation.
Gene expression: process that uses DNA to direct protein synthesis
Transcription:
-Produces an RNA copy or transcript of a gene
-Structural genes produce messenger RNA (mRNA) that specifies the amino acid sequence of a
polypeptide
-Translation:
-Process of synthesizing specific polypeptide based on the RNA sequence
Compare and contrast gene expression in prokaryotes and in eukaryotes. Where do Transcription and Translation occur? What extra step happens in eukaryotes?
Prokaryotes:
-Transcription: Cytoplasm
-Translation: Cytoplasm
Eukaryotes:
-Transcription: Nucleus
-Translation: Cytoplasm
-Third step: RNA processing where pre-mRNA is processed into a mature mRNA.
Describe the functions of each part of the gene.
Structural Gene: they code for an mRNA that will be read to make protein
Promotor: where RNA Polymerase binds to initiate transcription 3’ ATATT 5’
Terminator: where RNA Polymerase will leave the gene and terminate transcription
Regulatory sequences: where different proteins can bind and speed up or slow down transcription of the gene
Transcribed region: area that codes for mRNA sequence
Describe the three major steps during transcription, including the role of sigma factor (prokaryotes), transcription factors (eukaryotes), and RNA Polymerase.
- Initiation (Starting the process)
*In bacteria:
-A helper protein called sigma factor looks for a promoter.
-When promoter is found, it brings in RNA polymerase, the main enzyme that builds RNA.
*In eukaryotes (like humans):
-Transcription factors find the promoter and help RNA polymerase attach to the DNA.
- Elongation (Building the RNA strand)
-RNA polymerase copies template strand of DNA.
-Reads DNA in the 3’ to 5’ direction and builds the RNA in the 5’ to 3’ direction.
-Matches up RNA bases with the DNA bases
-RNA bases join together and make a growing RNA strand. - Termination (Ending the process)
-RNA polymerase continues until a stop signal (a termination sequence).
-Lets go of the DNA and releases the new RNA molecule.
-DNA goes back to normal, and transcription is done!
Describe the three steps of RNA processing (eukaryotes only) that occur after transcription. For each step: what is it? Where on the mRNA does it happen? Why do it?
- Splicing:
What happens?
-Spliceosome removes introns, puts exons back together
Where?
-Inside nucleus, middle of the RNA strand
Why?
-To keep only the parts of the RNA that are needed to make a protein.
-Alternative splicing- single gene can encode multiple polypeptides by varying which exons are combined
- 5’ Cap:
What happens?
-A special modified “G” nucleotide is added to the start of the mRNA.
Where?
-Inside nucleus, at the 5’ end (beginning of RNA).
Why?
-To exit the mRNA from nucleus and for ribosome binding
-Protects it from being broken down
- Poly-A tail
What happens?
-100-200 A nucleotides added to 3’ end
Where?
Inside nucleus, at the 3’ end of RNA,
Why?
Increases stability, lifespan in cytosol
Explain the functions of the following components during translation
mRNA: Carries the instructions for making a protein.
tRNAs: Correct amino acids to the ribosome
Ribosomes: Machine reads the mRNA and builds the protein
Start codons: Signals the start of translation
Stop Codons: Signals the end of the protein
Release factors: Ends translation and release the protein
Explain the significance of the reading frame during translation. What determines the reading frame? What happens if a mutation alters the reading frame—what type of mutation is that?
-The reading frame is how the mRNA is read in groups of 3 bases (codons).
-The Start codon defines the reading frame
-If the reading frame is altered by mutation, the same nucleotides can end up grouped differently.
-Frameshift mutation
Describe the three major steps during translation, including the role of the A site, P site, and E sites of the ribosome.
- Initiation:
-Small Subunit binds near 5’ end, slides down the mRNA until it finds 5’ AUG 3’, Charged tRNAMet binds to Start codon, Large Subunit binds on top - Elongation:
-Starting Point:
-The growing protein (polypeptide) is on a tRNA in the P site. The A site is empty.
-New tRNA Arrives:
-A charged tRNA (carrying an amino acid) enters the A site.
-tRNA anticodon pairs with the complementary and antiparallel mRNA codon.
- Peptide Bond Forms:
-The polypeptide is passed to the tRNA in the A site.
-Amino acid is attached to the C terminus of polypeptide
-Peptide bond attaches the amino acid to the polypeptide
-The P site tRNA is now uncharged - Ribosome Moves:
-Ribosome shifts one codon forward on the mRNA.
-The uncharged tRNA moves from the P site to the E site, and the uncharged tRNA leaves the ribosome
-The tRNA with the growing polypeptide moves to the P site.
-The A site is now empty, ready for the next charged tRNA. - Termination:
- A stop codon (UAA, UAG, or UGA) reaches the A site of the ribosome.
- A special protein called a release factor binds to the stop codon.
- The polypeptide (protein) is released from the tRNA in the P site and floats away into the cytosol.
4.The ribosome breaks apart:
-large/small parts of the ribosome separate.
-The mRNA and uncharged tRNA leave.
-The release factor detaches.
Define the types of mutations that occur in the DNA a
Substitution: Changed base sequence
Addition: Insertion of nucleotides
Deletion: Removal of nucleotides
Frameshift: when nucleotides are inserted or deleted
The different types of mutations in the DNA can lead to different results in the Amino Acid sequence. Describe the mutations that can result in the amino acid sequence using the table below.
Nonsense:
-Normal codon changes to a stop codon
-Protein stops too early/incomplete
Missense:
-One codon changes and gives a different amino acid
-Protein may work differently or not
Silent/Neutral:
-Codon changes, but the same amino acid is made
-Protein stays the same
Compare and contrast Spontaneous mutations and Induced mutations. Include the definition of the term mutagen.
*Spontaneous mutations are biological:
-Rates vary from species to species and from gene to gene
-Expected rate of background mutation approximately 1 mutation for every 1 million genes
-Happen during DNA replication, recombination, repair, or from natural toxic by-products of metabolism.
*Induced mutations are environmental:
-Detected when the mutation rate higher than the spontaneous mutation rate
-Mutagens are chemical or physical agents that can alter DNA
Define carcinogen. Are all carcinogens also mutagens? Explain.
-Carcinogen: substance or agent that can cause cancer
- No, not all carcinogens are mutagens.
-Some carcinogens cause cancer without directly mutating DNA, like by speeding up cell division.
Define somatic mutation and germ line mutation. Explain why somatic cell mutations are not passed on to offspring but germ cell mutations can be
*Germ-line cells give rise to gametes (eggs and sperm):
-Mutation can occur in a sperm/egg cell or in a cell that gives rise to eggs/sperm
-Germ line mutations are the only type of mutation that can be passed to offsrping
-Somatic cells are all other body cells:
-Mutation can occur early in development or later in life
-Only some body parts will have the mutation
-Most common mutation type involved in cancer
-Cancer is accumulation of many somatic cells
Explain the difference between chemical and physical mutagens and give some examples of each
Chemical Mutagens:
-Some chemicals cause abnormal base pairing: Modify bases, replace bases
-Others interfere with replication by distorting the shape of the double helix
Physical Mutagens:=
Ionizing Radiation:
-High energy (like X-rays, gamma rays).
-Can go deep into cells and create free radicals that damage DNA.
-Cause base deletions, breaks in 1 or both DNA
strands
Non-ionizing Radiation:
-Lower energy (like UV rays from the sun).
-Can only affect the surface and cause DNA damage, like thymine dimers (incorrect base pairing).
