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157 Cards in this Set
- Front
- Back
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Functional unit of genetic information is the _______.
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gene
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What are genes in cells composed of?
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DNA
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Name Three informational macromolecules in cell
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DNA
RNA Protein |
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Replication
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DNA is duplicated
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Transcription
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information from DNA is transferred to RNA
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mRNA stands for what?
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messenger RNA
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What does mRNA do?
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encodes polypeptides
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What does tRNA stand for?
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transfer RNA
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What does tRNA do?
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plays role in protein synthesis
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What does rRNA stand for?
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ribosomal RNA
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What does rRNA do?
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plays role in protein synthesis
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What is Translation?
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information in RNA is used to build polypeptides
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What is the central dogma of molecular biology?
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DNA to RNA to protein
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How are genes transcribed in Eukaryotes?
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each gene is transcribed individually
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How are genes transcribed in Prokaryotes?
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multiple genes may be transcribed together
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Four nucelotides found in DNA
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1. Adenine (A)
2. Guanine (G) 3. Cytosine (C) 4. Thymine (T) |
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Backbone of DNA chain is alternating ________ and the __________.
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1. phosphates
2. pentose sugar deoxyribose |
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What do phosphates connect?
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Phosphates connect 3′- carbon of one sugar to 5 of the adjacent sugar
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All cells and some viruses have _______________________.
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DNA in double- stranded molecule
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Two strands in double helix are ________.
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Two strands are antiparallel
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Two strands have __________ base sequences
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complementary
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Adenine always pairs with Thymine
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Adenine
Thymine |
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_______ always pairs with _______
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Guanine
Cytosine |
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What do two strands form?
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Two strands form a double helix
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How is the size of DNA molecules expressed?
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Size of DNA molecule is expressed in base pairs
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1,000 base pairs = ?
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1 kilobase pairs = 1 kbp
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1,000,000 base pairs = ?
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1 megabase pairs = 1Mbp
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What is the size of the E.Coli genome?
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4.64 Mbp
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Each base pair takes up _____ of length along the helix
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0.34 nm
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______ base pairs make up 1 turn of the helix
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10
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What are Inverted Repeats?
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Repeated sequence that is arranged in an inverse orientation
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What are stem loops and where are they most likely found?
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Short double-helical regions caused by nearby inverted repeats; common in RNA not DNA
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___________ between DNA strands hold two strands together
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Hydrogen bonds
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Adenine–Thymine pair has_____ hydrogen bonds and
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two
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Guanine– Cytosine pair has ______ hydrogen bonds
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three
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High heat breaks hydrogen bonds causing _____________.
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denaturation (melting)
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________ melts at higher temperatures than ________.
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GC rich DNA; AT rich DNA
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What is Supercoiled DNA?
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DNA is further twisted to save space
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What is negative supercoiled?
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double helix is underwound
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What is positive supercoiled?
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double helix is overwound
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What is relaxed DNA?
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DNA has number of turns predicted by number of base pairs
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What kind of coiling is predominantly found in nature?
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negative supercoiling
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What is DNA gyrase?
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introduces supercoils into DNA
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What is a genome?
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entire complement of genes in cell or virus
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What is a chromosome?
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main genetic element in prokaryotes
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Viruses contain either ______or ____ genomes
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RNA; DNA
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What shape can the viral genomes be?
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circular or linear
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How many strands can viral genomes have?
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one or two
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What do plasmids do?
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replicate separately from chromosome
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What are the 4 characteristics of plasmids?
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1. Great majority are double stranded
2. Most are circular 3. Generally beneficial for the cell (i.e., antibiotic resistance) 4. NOT extracellular, unlike viruses |
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___________ is a genetic element with “housekeeping” genes
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Chromosome
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_________ is a genetic element that is expendable and rarely contains genes for growth under all conditions
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Plasmid
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The presence of what is necessary for a genetic element to be a chromosome?
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Presence of essential genes is necessary for a genetic element to be called a chromosome
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What are transposable elements?
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Segment of DNA that can move from one site to another site on the same or different DNA molecule
--Inserted into other DNA molecules |
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What are 3 main types of transposable elements?
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1.Insertion sequences
2. Transposons 3. Special viruses |
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Genetic Elements
Organism: Prokaryote Element: Type of Nucleic Acid: Description: |
Element: Chromosome
Type of Nucleic Acid: Double stranded DNA Description: extremely long, usually circular |
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Genetic Elements
Organism: Eukaryote Element: Type of Nucleic Acid: Description: |
Element: Chromosome
Type of Nucleic Acid: Double stranded DNA Description: extremely long, linear |
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Genetic Elements
Organism: All organisms Element: Type of Nucleic Acid: Description: |
Element: Plasmid
Type of Nucleic Acid:Double stranded DNA Description: relitively short circular or linear molecule; extrachromosomal |
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Genetic Elements
Organism: All organisms Element: Type of Nucleic Acid: Description: |
Element: transposable element
Type of Nucleic Acid: Double stranded DNA Description:Always found inserted into another DNA molecule |
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Genetic Elements
Organism: Mitochondrion/Chloroplasts Element: Type of Nucleic Acid: Description: |
Element: genome
Type of Nucleic Acid: Double stranded DNA Description: medium length; usually circular |
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Genetic Elements
Organism: Viruses Element: Type of Nucleic Acid: Description: |
Element: genome
Type of Nucleic Acid: single or double stranded DNA Description: relatively short;usually circular or linear |
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DNA replication is ____________.
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semiconservative
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Each of the two progeny double helices have _________________.
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one parental and one new strand
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Precursor of each nucleotide is a _______________.
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deoxynucleoside 5′ triphosphate (dNTP)
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Replication ALWAYS proceeds from the ____ end to the ____ end
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5' end to the 3' end
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____________ catalyze the addition of dNTPs
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DNA polymerase
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______ different DNA polymerases in E. coli
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Five
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______________ is primary enzyme replicating chromosomal DNA
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DNA polymerase III
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What do DNA polymerases require?
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DNA polymerases require a primer; primers are made from RNA
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DNA synthesis begins at the ______________ in prokaryotes
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orgin of replication
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What is a the replication fork?
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zone of unwound DNA where replication occurs
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What unwinds the DNA?
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DNA helicase
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Where do DNA extensions occur continuously? discontinuously?
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Leading; lagging
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What are Okazaki fragments?
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appear on the lagging strand
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What does DNAgyrase do?
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unwinds supercoils ahead of replisomes
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What do orgin binding proteins do?
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binds origin of replication; aids DNA melting to open double helix
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What is Helicase loader?
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loads helicase at origin
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What does helicase do?
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unwinds double helix at replication fork
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What does a single-stranded binding protein do?
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prevents single strands from annealing
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What does primase do?
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primes new strands of DNA
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What does a polymerase subunit responsible for?
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strand elongation
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What does DNA polymerase I do? DNA polymerase III?
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excises RNA primer and fills in gaps; main polymerizing enzyme
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DNA synthesis is __________ in prokaryotes
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bidirectional
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What is bidirectional?
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Two replication forks moving in opposite directions
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DNA Polymerase III adds ________________.
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1,000 nucleotides per second
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complex of multiple proteins involved in replication
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Replisome
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DNA is pulled through the what?
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replisome
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What are mutation rates in cells?
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Mutation rates in cells are 10-8–10-11 errors per base inserted
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Polymerase can detect mismatch through ___________________.
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incorrect hydrogen bonding
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Proofreading occurs in ________, _________, and _______________
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1. prokaryotes
2. eukaryotes 3. viral DNA replication systems |
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Transcription (___________) is carried out by __________.
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DNA to RNA;
RNA polymerase |
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In transcription RNA precursors are :
1. 2. 3. 4. |
1. ATP
2. GTP 3. CTP 4. UTP |
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In transcription, What does RNA polymerase use as a template?
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DNA
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What is chain growth for transcription?
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Chain growth is 5′ to 3′ just like DNA replication
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How many of DNA are transcribed by RNA polymerase for any gene?
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Only one of the two strands of DNA are transcribed by RNA polymerase for any gene
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True or False?
Genes are not present on both strands of DNA, but at different locations |
false, they are present.
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RNA polymerase has _____ different subunits
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five
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RNA polymerase recognizes DNA sites called ________.
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promoters
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What are promoters?
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site of initiation of transcription
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Promoters are recognized by __________of RNA polymerase
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sigma factor
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Transcription stops at specific sites called ______________.
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transcription terminators
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Unlike DNA replication, transcription involves _____ units of DNA. What does this allow?
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smaller; Often as small as a single gene
Allows cell to transcribe different genes at different rates |
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Sigma factors recognize what two regions within promoters that are highly conserved?
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1. Pribnow box: located 10 bases before the start of transcription (-10 region)
2. -35 region: located ~35 bases upstream of transcription; conserved/sequences stay the same |
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Sigma binds with ______.
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premoter
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True or False?
Termination of RNA synthesis is governed by a specific DNA sequence |
true
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What are Intrinsic terminators?
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transcription is terminated without any additional factors
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What is Rho-dependant termination?
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Rho protein recognizes specific DNA sequences and causes a pause in the RNA polymerase
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What is the Unit of transcription?
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unit of chromosome bounded by sites where transcription of DNA to RNA is initiated and terminated
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What do most genes encode?
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proteins
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Which RNAs are not translated?
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rRNA and tRNA
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What are 3 types of rRNA?
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16S, 23S, and 5S
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______ cotranscribed with rRNA or other tRNA
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tRNA
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tRNA and rRNA are very ______.
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stable
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mRNA has a very short _______.
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half life(a few minutes)
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Prokaryotes often have genes related to the same process clustered together. How are they transcribed?
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These genes are transcribed all at once as a single mRNA
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An mRNA encoding a group of cotranscribed genes is called a _______________.
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polycistronic mRNA
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What is an operon and what does it allow for?
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a group of related genes cotranscribed on a polycistronic mRNA
-Allows for expression of multiple genes to be coordinately regulated |
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What is translation?
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the synthesis of proteins from RNA
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What is the genetic code?
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a triplet of nucleic acid bases (codon) encodes a single amino acid
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What is a degenerate code?
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multiple codons encode a single amino acid
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What recognizes a codon on tRNA?
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Anti-codon
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What is a wobble?
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irregular base pairing allowed at third position of tRNA
(first 2 have to match, third one doesn't.) |
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How many codons are there?
Amino acids? |
64; 20(more than one codon codes for an amino acid)
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What is the start codon and what does it code for?
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AUG; methionine; it's the first amino acid in a sequence
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What is the stop codon?
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UGA
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start codons are ______ codons
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sense--codes for an amino acid
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stop codons are ______ codons.
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nonsense--stops translation; doesn't code for an amino acid
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What do Stop codons do?
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signal the termination of translation
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What is the reading frame?
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triplet code requires translation to begin at the correct nucleotide
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What ensures the proper reading frame?
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Shine-Dalgarno sequence; base pair with ribosomal RNA
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What is an open reading frame?
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AUG followed by a number of codons and a stop codon in the same reading frame
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What is codon bias?
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multiple codons for the same amino acid are not used equally
-Correlated with tRNA availability -Cloned genes from one organism may not be translated by recipient organism because of codon bias -varies with organism |
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What is tRNA(transfer RNA)?
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at least one tRNA per amino acid
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Bacterial cells have ____ different tRNAs
Mammalian cells have _______ different tRNAs |
60;
100–110 |
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tRNA and amino acid brought together by ______________.
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aminoacyl-tRNA synthetases; ATP is required
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What shape is tRNA?
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tRNA is cloverleaf in shape
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Is RNA a single or double strand?
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single; folds back because of complimentary base pairs
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tRNA has ________ and mRNA has ______.
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anticodon; codon
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What is an anticodon?
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three bases of tRNA that recognize three complementary bases on mRNA
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Ribosomes
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sites of protein synthesis
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What are some characteristics of ribosomes?
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1. Thousands of ribosomes per cell
2. Composed of two subunits (30S and 50S in prokaryotes) 3. S = Svedberg units (centrifuge) 4. Combination of rRNA and protein 5. eukaryotes= 80s ribosomes 6. bacteria = 70S ribosomes 7. E.coli has 52 ribosomal proteins |
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What are the 3 steps of translation?
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1. Initiation
2. Elongation 3. Termination |
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What is Initiation?
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two ribosomal subunits assemble with mRNA
--Begins at an AUG start codon |
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What is elongation?
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amino acids are brought to the ribosome and are added to the growing polypeptide
--occurs at the A & P sites of the ribosome |
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What is translocation?
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part of elongation when, movement of the tRNA holding the polypeptide from the A to the P site
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What is polysomes?
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Part of the elongation process; a complex formed by ribosomes simultaneously translating mRNA
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Elongation
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forming polypeptides by amino acids hooking together by peptide bonds
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What is Termination?
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occurs when ribosome reaches a stop codon
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What are Release Factors (RF)?
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part of the termination process; recognize stop codon and cleave polypeptide from tRNA
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What happens during termination?
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--Release factors (RF): recognize stop codon and cleave polypeptide from tRNA
--Ribosome subunits then dissociate --Subunits free to form new initiation complex and repeat process |
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How do many antibiotics inhibit translation?
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by interacting with ribosomes
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What is a polysome?
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multiple ribosomes
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___ out of ___ codons code for an amino acid.
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61 out of 64
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How many amino acids does the universal genetic code code for?
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20
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What reshapes and refolds proteins to make sure it codes correctly?
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chaperonins
--they are not incorporated into protein |
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What are Signal sequences?
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found on proteins requiring transport from cell
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What are the characteristics of signal sequences?
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--15–20 residues long
--Found at the beginning of the protein molecule --Signal the cell’s secretory system --Prevent protein from completely folding |
