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173 Cards in this Set
- Front
- Back
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What is autophagy?
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-organelle turnover
-destruction of organelles and their replacement |
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what are the products of autophagy?
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residual bodies which have 2 possible fates:
1. released (exocytosis) 2. retained (lipofuscin granules) |
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What is the cytoskeleton?
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-a dynamic network of interconnected filaments and tubules that extends throughout the cytosol of eukaryotes
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Functions of the cytoskeleton?
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-structural support
-intracellular transport -contractility and motility -spatial organization within cells |
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Structural components of cytoskeleton?
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-microtubules (biggest)
-intermediate filaments (intermediate sized) -microfilaments (smallest) |
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Describe Microtubules (size, stability,compsition, motor proteins, function, polarity)
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Size: largest cytoskeletal element (25nm diameter)
Stability:very unstable Composition: polymer of proteins alpha and beta tubulin motor Protiens: dynein (minus end directed) and kinesin (plus end directed) Function: involved in cell movement structure: polar |
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what is rapid dissembly at the plus end of a microtubule called?
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catastrophe
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where are mictrotubules assembled?
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microtubule-organizing center
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what are the 2 major types of microtubules and what are their functions?
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1. Axonemal MT-highly organized and stable; involved in cell movement
2. Cytoplasmic MT- loosely organized, very dynamic |
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Name 2 classes of microtubule associated proteins (MAPS)
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1. Non-motor MAPS-control MT organization in cytosol
2. Motor MAPS- kinesin and dynein use ATP to generate force; move material along MT; generate sliding forced between MTs |
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Describe Intermediate Filaments (size, stability,compsition, motor proteins, function, polarity)
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Size: intermediate (10-12nm diameter)
Stability: stable relative to MTS and microfilaments Composition: alpha helical domains wrap around each other to form dimers which are alligned in anti-parallel motor proteins: none Function: provide structural support and mechanical strength structure: non polar |
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Describe Microfilaments (size, stability,compsition, motor proteins, function, polarity)
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Size: smallest (8nm diameter)
Stability: more stable then MTS but still unstable Composition: polymer of protein actin Motor Proteins: myosins Function: maintenance of cell shape, cell movement, cytokinesis, muscle contraction Structure: Polar |
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Describe the steps of Microfilament assembly
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1. Nucleation-very slow
2. Elongation-monomers quickly add to both ends; faster at plus end |
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Give 3 examples of actin-binding proteins and describe their functions
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1. Arp2/3- nucleating proteins
2. Profilin- monomer-polymerizing proteins 3. Cofilin- filament-depolymerizing proteins |
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What role to actin-binding proteins play in moving cells?
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The coordinated activity of actin-binding proteins controls microfilament formation in a lamellipodium to allow directed movement of cells
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What role does myosin play in the movement of cells?
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-myosn motors are attached to the actin in the trailing end of the cell
-myosin based contraction pulls the trailing end of the cell forward |
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Functions of the Nucleus
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-storage, replication and repair of genetic material
-expression of genetic material (transcription) -ribosome biosynthesis |
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structure of nucleus
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-nuclear envelope consists of the nuclear membrane, nuclear pores and nuclear lamina
-nuclear contents consists of the chromatin, nucleoplasm, nuclear matrix and nucleolus |
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What is the Nuclear Envelope(NE) constructed of?
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2 parallel phospholipid bilayers
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What is the outer membrane of the NE continuous with?
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the rough endoplasmic reticulum
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what is the function of the inner membrane of the NE?
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it bears integral proteins which connect to nuclear lamina
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Function of the nuclear envelope
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-separates nuclear content from cytoplasm
-allows limited movement of molecules between nucleus and cytoplasm -double membrane to protect the nucleus |
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what is nuclear lamina?
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-a thin meshwork of filamentous proteins
-bound to inner surface of NE |
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Function of nuclear lamina?
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-provide structural support to the nuclear envelope
-attachment sites for chromatin |
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What are nuclear pores?
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-gateway between cytoplasm and nucleoplasm
-place where inner and outer membranes fuse |
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What is the Nuclear Pore Complex (NPC)?
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-a large, supramolecular complex composed of nucleoporins that fits in the nuclear pore projecting into the cytoplasm and nucleoplasm
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Functions of the NPC
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-passive diffusion of small molecules (fast)
-regulated movement of larger molecules (slow) |
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what is the nuclear matrix?
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-network of insoluble proteins
-maintains shape and organization of the nucleus -organizes chromosomes -anchors machinery required for nuclear processes |
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What are nucleotides comprised of?
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-a phosphate group
-a five carbon sugar -and two of: uracil, cytosine, thymine, adenine and guanine |
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Name two pyrimidines
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-thymine
-cytosine |
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name two purines
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-adenine
-guanine |
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How are purine and pyrimidine nucleotides connected?
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-phosphodiester bonds
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How is double stranded DNA held together?
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-hydrogen bonds between bases on opposing strands
-hydrophobic interactions between adjacent stacked bases |
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How many hydrogen bonds hold thymine and adenine together?
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two
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how many hydrogen bonds hold cytosine and guanine together?
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three
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Are DNA strands polar?
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yes
-they have a 5' end with a free phosphate group and a 3' end with a free hydroxyl group |
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Opposing DNA strands are said to be __________
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complementary
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What is the most common type of DNA?
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B-DNA with major grooves and minor grooves
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The DNA in living cells is _________ ____________
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negatively supercoiled
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Chloroplast and mitochondrial DNA have what kind of chromosomes?
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circular chromosomes
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Eukaryotic chromosomes are composed of:
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-proteins
-DNA -RNA |
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first level of DNA condensation
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-packing DNA as a negative supercoil into nucleosomes
-DNA is wrapped around a nucleosome core of 8 histone proteins and anchored by a 9th -product is an 11nm diameter fibre |
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second level of DNA condensation
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-an additional folding or supercoiling of the 11nm fibre to produce a 30nm fibre
-driven by nucleosomal interactions |
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third level of DNA condensation
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attachment of the 30nm fibre at many positions to a nonhistone protein scaffold
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what is the basic structural unit of the metaphase chromosome?
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30nm fibre
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what is the metaphase chromosome?
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DNA in its most condensed form
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What is a telomere?
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-a cap placed on the ends of chromosomes to protect them from digestion
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Telomere Functions?
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-resist degradation by DNases
-prevent fusion of chromosomal ends -facilitate replication of the ends of the linear DNA |
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What is a centromere?
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-provides a point of attachment of chromosomes to microtubules in the mitotic spindle
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The Transforming Principle--> Griffith, 1928
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-Griffith injected mice with various combinations and types of the viruses IIIs and IIR and found either a dead mouse with living IIIs bacteria in it or a dead mouse
-this helped him determine either the protein or DNA from IIIS bacteria is being transferred to mice and killing them |
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The Transforming Principle--> Sia and Dawson, 1931-33
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-performed similar experiements to Griffith but used vitro cultures instead of mice and determined which bacteria resulted in colony growth
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The Genetic Material is DNA--> Avery, MacLeod & McCarty, 1944
PART ONE |
-isolated DNA to determine if it was causing colony growth or if protein was responsible
Results: -IIR grows normally -DNA from heat-killed IIIs cells results in no colonies -IIR cells and DNA from heat-killed IIIS cells combined results in IIIs colonies therefore somthing in IIIS DNA converts IIR |
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The Genetic Material is DNA--> Avery, MacLeod & McCarty, 1944
PART TWO |
-similar to part one but DNA, RNA and protein were isolated individually
-type IIR cells and heat-killed IIIS were mixed -it was found no IIIS colonies were formed without IIIS DNA -when RNA and Protein were removed the colonies still formed |
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The Genetic MAterial is DNA--> Hershey and Chase, 1952
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-experiment was done to determine if DNA could transfer
-determines only DNA transfers from virus to cell, not protein |
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Fraenkel-Conrat, 1957
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-determined some viruses use RNA as their genetic material
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The Transfer of info from DNA to Protein
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Step 1. DNA is transcribed to mRNA
step 2. mRNA is translated to protein |
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Differences in DNA and RNA
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-RNA has pyrimidine uracil instead of thymine
-RNA sugar is ribose -DNA sugar is deoxyribose (no hydroxyl group n 2' Carbon) |
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General features of Transcription
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-only one strand of DNA acts as a template
-template strand is always read 3' to 5' -new strand will be made 5' to 3' -DNA double helix is locally unwound during transcription by RNA polymerase |
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How is information transfered from DNA to protein?
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Step 1: Transcription DNA-->mRNA
Step 2: Translation mRNA-->Protein |
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What positions the RNA polymerase at the begining of transcription and causes it to dissociate at the end of a gene?
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DNA sequences
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Transcription Initiation (Prokaryotes)
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-polymerase binds to a specific sequence (-10, -35)
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Why does Polymerase bind to the -10 sequence?
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-the -10 sequence is made up of many ATs and is easier to unwind because there is less bonds between A and T
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Transcription Elongation (Prokaryotes)
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-in prokaryotes genes are close together and several can be encoded on a single RNA molecule
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Transcription Termination (Prokaryotes)
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-a transcription terminator sequence stops transcription (p-rho-independent)
-transcription of the termination sequence results in hydrogen bonded hairpin |
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Transcription Initiation (Eukaryotes)
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-polymerase recruited by transcription factors binding to the TATA box and other promoters
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Transcription Elongation (Eukaryotes)
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-similar to prokaryote elongation but 5' caps are added to the mRNA
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what is the function of a 5' cap?
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-to protect and assist in translation
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Transcription Termination (Eukaryotes)
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-cleavage occurs at a defined sequence
-Poly-A tails are added to the 3' end -introns are spliced out |
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What are introns?
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-noncoding sequences located between coding squences
-variable in size -removed from the pre-mRNA and are not present in mature mRNA |
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what are exons?
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-both coding and noncoding sequences
-remain in the mature mRNA after splicing |
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Translation: Prokaryotes
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-ribosomes bind to Shine-Dalgarro sequence, start translating at AUG
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Translation: Eukaryotes
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-the mRNA is scanned 5' to 3' until an AUG start codon is found and translation can begin
-proteins are assembled on the ribosome according to the mRNA sequence (genetic code) -tRNA matches the correct amino acid to each codon |
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why can transcription and translation occur simultaneously in prokaryotes?
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because prokaryotes lack a nucleus
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The Genetic Code
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-codons are adjacent with no spaces
-each nucleotide is part of one condon, no overlapping -most amino acids are specified by more than one codon -amino acids with similar properties are specified by related codons -each codon has the sa meaning in all organisms |
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Termination terminates at specific codons, describe the steps
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step 1: Release factor 1 binds to the UAG (or UAA or UGA) termination codon in the A site of the ribosome and tRNA leaves the E site
Step 2: Release of the nascent polypeptide and Release Factor 1 and transfer of tRNA from the P site to the E site Step 3: Dissociation of the mRNA-tRNA complex |
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What are the mitotic cells in humans?
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stem cells
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what is each mitotic chromosome comprised of?
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a pair of sister chromatids
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What is mitosis?
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-cellular organelles and cytoplasmic contents are divided more or less equally between daughter cells
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how are mitochondria and chloroplasts divided between daughter cells?
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randomly
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how must nuclear chromosomes be distributed to daughter cells?
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nuclear chromosomes must be duplicated exactly and distributed equally and exactly to dauhter cells
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How long does it take a human cell to go through one cell cycle?
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approximately 24 hours
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The main stages of the cell cycle
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G1 Phase- growth, cellular metabolism
S Phase- DNA replication G2 Phase- preparation for mitosis M Phase-chromosomal separation and cytokinesis Interphase-the time between successive mitoses (G1 + S + G2) |
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what is cytokinesis?
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-the cytoplasmic division bringing about the separation into 2 daughter cells
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when mitosis begins, each chromosome has been ________
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duplicated
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what influences condensation of chromosomes?
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condensin
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Interphase
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-Chromosomes duplicate to produce sister chromatids
-sister chromatids are joined at the centromere by cohesin -the centrosome is duplicated |
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Prophase
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-initiation of spindle formation
-condensation of duplicated chromosomes -framentation of ER and Golgi -nucleolus disappears -nuclear membrane starts to break down -spindle microtubules invade the nuclear space |
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Prometaphase (intermediate)
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-chromosomal mictrotubules attach to the kinetochores, which are on the outer surface of centromeres
-chromosomes move towards the equator of the spindle |
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Metaphase
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-duplicated chromosomes are aligned midway between the spindle poles
-this equatorial plane is called the metaphase plate -nuclear membrane broken down |
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Anaphase
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-centromeres split and chromatids separate
-chromosomes move towards opposite spindle poles -spindle poles move further apart |
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Telophase
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-chromosomes cluster at opposite spindle poles
-chromosome become dispersed and decondense -nuclear envelope assembles around chromosomes -Golgi and ER reform -daughter cells form by cytokinesis |
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difference between mitosis and meiosis
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mitosis-separation of sister chromatids to get two identical cells
meiosis-the splitting of homologous mom and dad chromosomes to get 4 gametes each with half the DNA |
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Meiosis occurs in two cell divisions, called?
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meiosis I
meiosis II |
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Prophase I: Leptonema
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chromosomes, each consisting of 2 sister chromatids, begin to condense
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Prophase I: Zygonema
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homologous chromosomes being to pair
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Prophase I: Pachynema
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homologous chromosomes are fully paired
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Prophase I: Diplonema
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homolegous chromosomes separate, except at chiasmata
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Prophase 1: Diakinesis
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Paired chromosomes condense further and become attached to spindle fibers
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What is pairing of homologous chromosomes called?
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synapsis
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How is synapsis made easier?
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by the formation of a synaptonemal complex, which is filled with proteins which can assist in meiosis
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what is recombination?
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-occurs during pachynema
-involves the breakage of chromatids and the exchange of the broken pieces between homologous chromosomes |
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Does recombination occur if synapsis doesnt?
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yes
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Metaphase I
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-paired chromosomes align on the equatorial plane in the cell
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Anaphase I
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-homologous chromosomes disjoin and move to opposite poles of the cell
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Telophase I
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chromosome movement is completed and new nuclei begin to form
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what does meiosis I produce?
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two haploid daughter cells that are genetically distinct
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Prophase II
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chromosomes, each consisting of two sister chromatids, condense and become attached to spindle fibers
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Metaphase II
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chromosomes align on the equatorial plane in each cell
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Anaphase II
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sister chromatids disjoin and move to opposite poles in each cell
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Telophase II
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chromosomes decondense and new nuclei begin to form
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Cytokinesis
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the haploid daughter clls are now separated by cytoplasmic membranes
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Spermatogenesis in mammals
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first mitosis of a diploid cell then meiosis occurs to create four haploid cells which differentiate to form mature gametes
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Oogenesis in mammals
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-begins with meiosis of the diploid cell to produce haploid cells which mature into gametes
-usually only one matures into an egg, the other three cells (polar bodies) degenerate |
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Yeast
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-even though yeast is haploid it can still underg mitosis during asexual reproduction, this is called budding
-the daughter nucleus (bud) is separated from the mother cell by cytokineis -sexual reproduction occurs when two haploid cells of opposite mating types come together and form a diploid cell which then undergoes meiosis |
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Male Gametophyte
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-each microspore mother cell undergoes meiosis to form 4 haploid microspores
-each microspore then undergoes mitosis to porduce a pollen grain containing sperm cells -the pollen grain and its contents are the male gametophyte |
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Female Gametophyte
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-each diploid megaspore mother cell undergoes meiosis to produce 4 haploid cells
-3 of these cells degenerate leaving only one functional mitotic product which becomes a megaspore -the haploid nucleus then undergoes 3 mitotic divisions to produce 8 identical haploid nuclei in a embryo sac -during cytokinesis 6 of the 8 nuclei become separated by cell membrane -one of these cells becomes the egg in the embryo sac and two become synergid cells -the other 3 cells will degenerate -the two remaining nuclei form a diploid nucleus and the embryo sac becomes the female gametophyte |
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Plant Fertilization
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-when a mature pollen grain lands on a stigma a pollen tube grows down to the egg cell in the ovary
1. one sperm cell within the pollen tube fuses with the egg cell in the female gametophyte to form the diploid zygote which will be grown into an embryo 2. the other sperm cell nucleus combines with the diploid secondary endosperm nucleus in the female gametophyte to form the triploid endosperm nucleus which will direct the development of nutritive tissue (endosperm) to feed the embryo |
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Benefits of Mendel's experimental system
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-peas were highly inbred and therefore bred-true so Mendel could easily study one trait at a time
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homozygous
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both alleles are identical
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heterozygous
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the two alleles are different
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Monohybrid cross
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-homozygous parents with different phenotypes are crossed and the F1 generation only shows the dominant phenotype
-the F1 generation are crossed and their offspring (F2) show both phenotypes with a ratio of 3 dominant: 1 recessive |
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Mendel's Principle of Dominance
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-in a heterozygote, one allele may conceal the presence of another
ex. F1 progeny had both alleles but only showed one phenotype because one allele hid the other |
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Mendel's Principle of Segregation
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Neither allele is typically changed by coexisting with the other in a heterozygote
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Dihybrid cross
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-two organisms homozygous for two traits each are crossed
-resulting in heterozygous offspring (F1) -F1 self-fertilizes and yeilds four different phenotypes in a 9:3:3:1 ratio |
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Mendel's Principle of Independent Assortment
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The alleles of different genes assort/segregate independently of each other
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The Multiplicative Rule
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-if the events A and B are independent, the probability that they occur together is the product of their individual probabilities of occurrence p(A)xP(B)
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The Additive Rule
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-if the events A and B are indepdendent and do not overlap, the probability that at least one of them occurs is the sum of their individual probabilities P(A)+P(B)
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Test Cross Function
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since a heterozygote and homozygote dominant may have the same phenotype a test can be performed to determine the individuals genotype
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Test Cross Procedure
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-the individual of unknown genotype must be crossed with a homozyous recessive individual
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Dominance in Pedigrees
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-every affected individual has at leas one affected parent
-the trait is manifested in at least one individual every generation once that trait appears |
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Resessive Traits in Pedigrees
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-the trait suddenly appears in the pedigree
-the trait skips generations |
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why do phenoypic ratios deviate significantly from Mendelian expecations in human families?
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because human families are small
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Binomial Probability
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-calculates the probability that out of n progeny exactly x will fall into one class and y into the other
[n!/x!y!] p^x(q^y) n=sample size x=# in one class y=#in other class p= probability of one class q= probability of the other class |
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Tautomers (spontaneous mutations)
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-rare forms of nitrogenous bases have altered base pairing properties
-if isoforms are replicated they will cause change in the DNA sequence and therefore mutations |
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hot spots for spontaneous mutations
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1. simple repeats -polymerase will slip and generate more repeats
2. symmetrical repeats (hairpins)-polymerase will skip this 3. Palindromes |
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Induced Mutations
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-mutations can be induced by mutagens like chemicals or exposure to radiation
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Dimerization
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-absorption of UV energy by pyrimidines results in dimerization which puts a kind in the DNA strand
-polymerase may get stuck on the kink during replication and cause a mutation |
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Silent Mutation
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a change in a single base pair that doesn't change the amino acid that is coded
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Nonsense Mutation
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a change in a single base pair that codes for a stop codon; the protein will be shorter than normal
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Missense Mutation
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-a new amino acid is coded for
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Conserved Missense
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-the new amino acid has similar properties to the old one
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Non-conserved Missense
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-the new amino acid does NOT have similar properties to the old one
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Inertions and Deletions
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-a single nucleotide insertion/deletion changes every amino acid after it because the reading frame is shifted
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Transposable Elements
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-mutations induced by DNA itself
-the transposable genetic element jumps to a different location and this can result in a inactive truncated polypeptide |
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Expanding Genes
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-many human inherited disorders result from expanding triplet/trinucleotide repeats
-the expanding triplet repeat diseases can show increased severity and/or earlier onset from one generation to the next |
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Losing Protein Function
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1. Mutations that affect the coding region change the protein to a non-functional form by changes to protein foling or post translational modification
2. Mutations that affect non-coding regions prevent or reduce tranription and translation |
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wild type
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the most common allele in a gene with more than two alleles, all other alleles are considered mutants
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Polymorphism
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the existence of 2 or more variants in a populations of individuals, with at least two of the variants having frequencies greater than 1%
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What makes an allele recessive?
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recessive mutations almost always involve a loss of gene function
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null allele
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complete loss of function
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hypomorphic allele
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partial loss of function
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what makes an allele dominant?
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an allele is dominant if it has the same phenotype in heterozygotes as in homozygotes
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dominant mutations can involve:
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a loss or gain of protein function
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dominant negative mutation
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a loss of function mutation that interferes with the normal function of the wild type allele
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gain of function mutation
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enhances the normal function of the gene
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Imcomplete Dominance
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-the phenotype of the heterozygote is midway between the phenotypes of the two homozygotes
-one allele is partialy or incompletely domiant over the other |
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codomiance
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-the heterozygote expresses the phenotypes of both homozygotes
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effects of mutations varry
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visible mutations
sterile mutations lethal mutations |
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complementation test for allelism
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-testing wheather 2 alleles that confer a particular phenotype are from the same gene
-must use recessive mutants, can't be done with dominant alleles |
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what factors influence phenotypes?
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genetic and environmental
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Conditional Mutations
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-expressivity is environmentally-dependent
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Pleiotropic
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a gene that effects many phenotypes
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Incomplete Penetrance
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-individuals do not express a trait even though they have the appropriate genotype
-clearly dominant because it appears in every generation |
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Variable Expressivity
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- a trait is not manifested uniformly among individuals that show it
-genetically they all have the same mutations but they all show different phenotypes -could be due to environment or genetic backround |
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Gene Interactions
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-different combinations of alleles from 2 genes result in different phenotypes
-these 2 alleles are influencing each other even though they are independently assorted |
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Epistasis
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-in epistasis an allele of one gene overrides the effect of other genes on the phenotype
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how do different cell types differentiate?
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-all cell types have the same DNA, it is the expression of the different genes that makes them different ie. they have different mRNA
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Are genes lost in the course of cell differentiation?
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-cloning says no
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complexity
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humans don't have many more genes than a fruit fly but we have more DNA therefore more complex
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Transcription and Gene regulation
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-transcription regulates gene expression in eukaryotes
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what is transcipon in eukaryotes regulated by?
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interactions between proteins and DNA sequences
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Basal Transcription Factors
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-are poteins that bind to specific sequences within the promoter to facilitate RNA polymerase binding
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Regulatory Transcription Factors
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-are proteins that bind to sequence elements in promoters or enhancers, thereby facilitating the function of the basal transcription factors and RNA polymerase
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