Chapter 7 Flashcards
DNA Structure and Gene Function
DNA definition
-a single molecule of nucleic acid
-made up of many monomer subunits called nucleotides
-stores information that the cell needs to produce proteins
How did scientists discover DNA?
Frederick Griffith
-Frederick Griffith’s experiment showed that some unidentified substance in a lethal strain of bacteria could transfer a harmless strain into a lethal strain
-later it was discovered that DNA was transmitted between toxic and harmless bacteria
-Griffith’s research showed that a lethal strain of bacteria (type S) could transfer a then unknown molecule to nonlethal bacteria (type R)
-Avery added enzymes that destroyed either proteins or DNA to show that DNA changed the Type R bacteria
How did scientists discover DNA?
Alfred Hershey and Martha Chase
-changing DNA changes properties of cells
-Alfred Hershey and Martha Chase showed that DNA, not protein, contains genetic information
-they used radioactive sulfur to label protein coats and bacteriophages and radioactive phosphorous to label DNA bacteriophages. Both infected bacteria. Protein infected didn’t show any radioactivity. DNA infected showed radioactivity. So, DNA, not protein, is genetic material
What is each DNA nucleotide consist of?
-one phosphate group
-one molecule of the 5-carbon sugar deoxyribose
-one nitrogenous base (either adenine, guanine, cytosine, or thymine)
One DNA molecule is made of how many nucleotides?
2 strands of nucleotides that wind together into a helical shape
(double helix)
DNA strands are held together by…
Base pairing
-hydrogen bonds form between nitrogenous bases to connect the 2 DNA strands together
-adenine bonds with thymine (A-T)
-guanine bonds with cytosine (G-C)
How are DNA strands antiparallel?
-each end of the DNA strand is different, either 5’ or 3’
-5 prime- where the phosphate group is attached to deoxyribose
-3 prime- where the OH group is attached to deoxyribose
-the 2 strands are antiparallel, oriented in 2 different directions, with 1 upside down in respect to the other
What is at the end of the 5 prime and and the 3 prime end?
-3’ end of nucleic acid strands terminates at the 3rd carbon of a sugar molecule
-5’ end of nucleic acid strand terminates at the 5th carbon of a sugar molecule
Define purines and pyrimidines and how they pair with each other
-purines- 2 ring structure (A & G- adenine and guanine)
-pyrimidines- single ring structure (C & T- cytosine and thymine)
-purines and pyrimidines pair with each other in hydrogen bonds
Define gene
A sequence of DNA nucleotides that encodes a specific protein or RNA molecule
Define chromosome
A DNA molecule wrapped around proteins in the nucleus of a eukaryotic cell
-also the genetic material of a prokaryotic cell
Define genome
All the genetic material in a cell
DNA vs RNA
-DNA is double strand, deoxyribose sugar, nucleotide bases: adenine, guanine, cytosine, and thymine
-DNA stored RNA and protein encoding information, transfers information to the next generation of cells
-RNA- single strand, ribose sugar with 1 oxygen, nucleotide bases: adenine, guanine, cytosine, and uracil
-RNA carries protein encoding information, helps to make proteins, catalyzes some reactions
Protein production occurs in what 2 stages?
-transcription (RNA synthesis) production of RNA using DNA as a template
-translation (protein synthesis) assembly of amino acid chain according to the sequence of nucleotides in mRNA
How many base pairs of genetic information in each nucleus?
6.4 billion pairs of genetic information in each nucleus
Define promoter
A control sequence at the start of a gene
-it attracts RNA polymerase and transcription (in eukaryotes)
Define RNA polymerase
An enzyme that uses a DNA template to produce a molecule of RNA
Define terminator
Sequence in DNA that signals where a gene’s coding region ends
What are the 3 types of RNA that carry out translation?
-messenger RNA (mRNA)
-ribosomal RNA (rRNA)
-transfer RNA (tRNA)
Define codon
A 3-nucleotide sequence that encodes 1 amino acid (polypeptide) or a stop signal
Define anticodon
3-base portion of a tRNA molecule, it is complementary to 1 mRNA codon
What does mRNA do?
-brings the information (code words celled codons)
-encodes the amino acid sequence
What does rRNA do?
-makes up the ribosome
-it’s the physical location of translation
-associated with proteins to form ribosomes, which structurally support and catalyze protein synthesis
What does tRNA do?
-brings the amino acids
-binds mRNA codon to one end and an amino acid to the other end
-physically links the message in mRNA to the amino acid sequence and encodes it
-includes anticodons
How many genes does the human genome have?
20,000-25,000 genes scattered on its 23 pairs of chromosomes
DNA pairings with RNA
DNA—-> RNA
adenine- uracil
cytosine- guanine
guanine- cytosine
thymine- adenine
Define exons
-coding sections for proteins
-the sequence that specify amino acids
-100-300 nucleotides
Define introns
-noncoding sections
-removed from the RNA
-1,000 nucleotides
Define intron splicing
Proteins and RNA called spliceosomes remove the intron sections and joins the exon sections before translation
What are the 3 steps of transcription and translation?
-initiation
-elongation
-termination
What happens in transcription initiation
-RNA polymerase gets it started, it binds to the promoter (the beginning of the gene)
-RNA polymerase also unwinds (unzips) the 2 short strands of DNA, exposing it
-DNA is the template, it will encode the RNA molecule
-the other strand of DNA doesn’t participate in the transcription
What happens in transcription elongation?
-RNA polymerase synthesizes RNA, it moves along the template strand, making and RNA copy along the way in a 3’ to 5’ direction
-RNA nucleotides bases pair with the template strand and the RNA polymerase joins them together into a strand of RNA
-RNA is antiparallel to DNA (3’ end matches to 5’ end)
What happens in transcription termination?
-RNA polymerase reaches the end, it reaches the terminator (the region of DNA found at the end of the gene), the RNA is now complete
-at the terminator, the RNA, DNA, and RNA polymerase separate from each other and the DNA becomes a double helix again
-the cell produced a copy of a gene
What happens after transcription but before translation?
-RNA isn’t totally ready yet, the cell must modify the RNA before it can carry out its function
-a “cap” structure is added to the 5’ end of mRNA
-a poly-A tail structure is added to the 3’ end of mRNA
-introns are removed from the mRNA sequence
-the RNA is now ready for translation, it’s now a functional molecule
-the RNA can now leave the nucleus to move to translation
Where does transcription and translation happen?
-transcription- in the nucleus
-translation- at the ribosomes, then it will either be free in the cytoplasm or attach to the rER
What happens in translation initiation?
-RNA is the template now
-small ribosomal subunit binds to mRNA
-large ribosomal subunit binds to the small subunit, sandwiching the mRNA
-initiator tRNA molecule binds, its anticodon matches up with the start codon in mRNA
-tRNA is the adaptor
Define genetic code
Correspondence between specific nucleotide sequences and amino acids
What happens in translation elongation?
-amino acids are joined together
-the second tRNA enters the ribosome next to the initiator tRNA, its anticodon matches the second mRNA codon
-the amino acids are joined together when enzymes in the ribosome form a polypeptide bonds (met-gly)
-amino acids are covalently bonded to each other
-the first tRNA leaves the ribosome, but its amino acid stays behind
-the ribosome moves to the right and a third tRNA comes in (its anticodon matches with the third mRNA codon
-enzymes form another peptide bonds to join the amino acids
What happens in translation termination?
-release factors end the process
-the ribosome reaches the stop codon, which is at the end of the gene
-a protein called release factor binds to the stop codon. there is no tRNA that can bind here, so no more amino acids will be added
-the protein is complete, the polypeptide detaches from the mRNA and folds into a functional protein
How is translation efficient?
-multiple ribosomes attach to an mRNA molecule simultaneously, so the cell can make many molecules of protein all at once
How is gene expression regulated?
-gene expression requires a lot of energy
-cell can save that energy by only producing the needed proteins
-both prokaryotes and eukaryotes regulate gene expression but in different ways
What is typically the first codon in mRNA?
AUG which is methionine
What are the codons that signify “stop”?
UGA, UAA, and UAG
What does ribosomes consist of?
-one small subunit
-one large subunit
-built of rRNA and proteins
What needs to happen to polypeptides for them to become a functional protein?
-must be folded
-some amino acids are cut from the chain
-sometimes multiple polypeptides join together to form a finished protein after translation
How do prokaryotes regulate several genes at once?
-genes in prokaryotes are organized into operons (groups of genes that are always transcribed together)
-lac operons include 3 genes that encode lactose-digesting enzymes plus a promoter and operator
Define promoter
-the region of the DNA where RNA polymerase binds to initiate transcription
Define repressor
-in an operon, a protein that binds to the operator and prevents transcription of genes
Define enhancer
-DNA sequence that helps regulate gene expression and lies outside the promoter
Define operator
-the region of DNA where regulatory proteins bind, which can affect the activity of RNA polymerase
-in an operon, the DNA sequence between the promoter and the protein encoding regions
Prokaryotes- repressor proteins block transcription
-when lactose is absent, lactose-digesting enzymes are not needed, the cell would be wasting energy producing those enzymes
-when lactose is present, it binds to the repressor, changes its shape, and releases the operator (protein synthesis of lactose-digesting enzymes now occur)
Eukaryotes have multiple levels of gene regulation
-in eukaryotes, gene regulation starts with the nucleus
-some genes are wound up very tightly and can’t be used for transcription, but other genes are available
Eukaryotes have transcription factors
-many different proteins called transcription factors can bind to a gene to affect the activity of RNA polymerase
-transcription of the gene can only occur if the correct transcription factors are present
Why does RNA polymerase need transcription factors?
-proteins called transcription factors bind to nucleotide sequences in genes called enhancers
-RNA polymerase can only become activated when the correct transcription factors are present
Define operon
- a group of related genes plus a promotor and operator that controls the transcription of the entire group
Eukaryotic genes can be regulated by splicing
-some eukaryotic genes can encode proteins by using different combination of exons
-alternative splicing creates different proteins from the same mRNA
RNA export can be regulated
-gene regulation continues into the cytoplasm
-certain eukaryotic proteins can hold mRNAs inside the nucleus, preventing them from reaching a ribosome
RNA can be regulated
-some RNA may be quickly degraded before its translated into a protein
-other mRNA may be silences by microRNA (short sequences of nucleotides that bind to the mRNA and prevent translation
Proteins can be regulated
-proteins must be properly folded before they are functional
-misfolded proteins are degraded
-they must also reach their correct cellular location
-cells can add or remove chemical modifications to proteins that change protein activity or cause proteins to become degraded
Define epigenetics
-the study of changes in gene expression that don’t involve changes in DNA sequence
Define transcription factor
-in eukaryotic cell, a protein that binds to a gene’s promoter and regulate transcription
Investigating life: clues to the origin of language
-FOXP2 is the “language gene”
-few amino acids differ between FOXP2 genes of humans, primates, and mice
-two recent mutations in the human genome might set our language skills apart from those of our ancestors
Define mutation
-a change in a cell’s DNA sequence
-mutations come in several varieties
-original sentence: the one big fly had one red eye
Different types of mutations
-substitution (missense)
-substitution (nonsense)
-insertion
-insertion (frameshift)
-deletion
-expanding repeat
Define substitution mutation
-the replacement of one nucleotide in a gene with another
-thQ one big fly had one red eye
Define missense mutation
-type of substitution mutation
-the altered codon specifies a different amino acid from original version
-thQ one big fly had one red eye
Define nonsense mutation
-type of substitute mutation
-the altered codon specifies “stop” instead of an amino acid
-the one big
Define insertion mutation
-addition of 1 or more nucleotides to a gene
-the one big WET fly has one red eye
Define frameshift mutation
-nucleotides are added or deleted by any number other than a multiple of 3, altering the reading frame
-the one Qbi gfl yha don ere dey
Define deletion mutation
-removal of one or more nucleotides from a gene
-the one big had one red eye
Define expanding repeat mutation
-the number of copies of a 3 or 4 nucleotide sequence increases over several generations
-gen 1: the one big fly had one red eye
-gen 2: the one big fly fly fly had one red eye
-gen 3: the one big fly fly fly fly fly had one red eye
Define mutagen
-any external agent that causes a mutation
Define transposable element
-DNA sequence that can move within a genome
-transposon for short
Define germline mutation
-a DNA sequence change that occurs in the cells that give rise to gametes (sperm and egg cells)
Define somatic mutation
-a DNA sequence change that occurs in non sex cells
Define allele
-one of two or more alternative forms of a gene
Define homeotic gene
-any gene that, when mutated, leads to organisms with structure in the wrong places
How can some mutations cause disease?
-a single base substitution in a hemoglobin gene cause blood cells to form abnormally, leading to sickle cell disease
Define silent mutation
-type of substitution mutation
-altered codon specifies the same amino acid as the original version
