realizată de Erika Garcia 3 ani în urmă
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repressors: decreases level of transcription = less mRNA
activators: increases level of transcription = more mRNA
when activators are bound, it will cause the DNA to bend to bind to the mediator proteins to increase transcription
when different proteins are needed in different organs, one organ (ex. liver) may have an activator protein for one protein (ex. albumin) that the other organ (ex. eye) may not have; helps different organs have different functions from each other
Needs to continuously add primers to the lagging strand to make several Okazaki fragments
Okazaki fragments are eventually covalently combined by DNA Ligase
Replicates in multiple, small segments called Okazaki Fragments that each need and RNA primer
Only 1 RNA primer is required for the replication of the leading strand
DNA replication proceeds bi-directionally
Replication forks: Y-Shaped regions at each end of the replication bubble where DNA is unwound
Eukaryotes have multiple ORIs
Prokaryotes have 1 ORI
Covalently joins together Okazaki Fragments in lagging strands
Replaces RNA Primers with DNA
Builds new DNA strand using the old DNA strand as a template
Creates RNA Primers
Binds to and stabilizes single stranded DNA
Unwinds DNA double helix at the replication fork
Relieves DNA supercoiling ahead of replication fork
Live R Strain + Heat-Killed S Strain
Heat-Killed S Strain
Live R Strain
The mouse lived
Live S strain
The mouse died
Free hydroxyl group at the 3' ends
Free phosphate group at the 5' ends
A mature mRNA strand is formed.
The last process is called RNA splicing. A complex made out of RNA and proteins called spliceosomes splices certain sequences in DNA. Intron sequences are removed and exon sequences are joined together.
An enzyme called polyA polymerase adds a polyA tail (AAAAAA) to the 3' end of the pre-mRNA strand.
A guanine nucleotide modifies the 5' end of the pre-mRNA strand by adding a 5 CAP.
A sequence in the RNA called the polyadenylation signal sequence (AAUAAA) stops transcription. Proteins make a cleavage in pre-mRNA to release the strand.
RNA polymerase II reads the template strand (3' to 5') to make the RNA in the 5' to 3' direction. It adds nucleotides to the template strand to make RNA. It creates downstream.
RNA Polymerase II binds to the promoter with additional transcription factors to create the transcription initiation complex. It begins unwinding DNA at the transcription start point (+1) to begin RNA synthesis.
Proteins called transcription factors bind to the promoter before RNA Polymerase II.
A sequence in RNA is the signal for the transcription process to stop. Once done, a mRNA strand is made.
RNA polymerase reads the template strand (3' to 5') to make the RNA in the 5' to 3' direction. It adds nucleotides to the template strand to make RNA. It creates downstream.
RNA polymerase unwinds DNA strand and start creating the RNA strand at the transcription start point. (+1)
RNA Polymerase binds to the promoter which is upstream.
60S consisting of 45 proteins
Separate from small ribosomal subunit unless mRNA is attached
40S consisting of 33 proteins
Occurs in the E site (exit site) of the ribosome; a stop codon is reached in the A site meaning translation no longer occurs. A release factor, also present in the A site, releases tRNA from mRNA and tRNA exits. A GTP driven process. Ribosomal subunits separate.
Occurs in the P site (peptidyl tRNA) of the ribosome; Formation of peptide bonds, formed by peptidyl transferase, between amino acids to form a polypeptide chain. Once a stop codon is reached, the carboxyl end of the polypeptide chain is detached from tRNA.
tRNA first binds to the 5' cap of mRNA and scans the mRNA until the start codon AUC is found. It then binds the UAG anticodon to begin the translation process; Met is the first amino acid attached to tRNA. GTP is required.
Large Ribosomal subunit
50S consisting of 31 proteins
Small Ribosomal subunit
30S consisting of 21 proteins
Termination
Occurs in the E site (exit site) of the ribosome; a stop codon is reached in the A site meaning translation no longer occurs. A release factor, also present in the A site, releases tRNA from mRNA and tRNA exits. A GTP driven process.
Elongation
Occurs in the P site (peptidyl tRNA binding site); Formation of peptide bonds btwn amino acids via peptidyl transferase; Adds more amino acids to the polypeptide chain until a stop codon is reached on the mRNA. Once a stop codon is reached, the carboxyl end of the polypeptide chain is released from tRNA.
Initiation
Occurs in A site (aminoacyl-tRNA) of the ribosome; UAG anticodon on tRNA binds to AUC codon on mRNA. The initiator tRNA also carrying the first amino acid, f-Met. This process requires GTP.
As H+ is heavily concentrated in the intermembrane space of the mitochondria, they will want to travel back inside down the concentration gradient with the help of ATP synthase (facilitated diffusion)
As the H+ travel down the gradient, the energy released (proton motive force) is used to add an inorganic phosphate to ADP to form ATP (aka osmosis)
Pumping of H+ protons into the intermembrane space from the matrix; H+ protons come from the NADH and FADH2 created in the Kreb's Cycle
Pumping of protons into the intermembrane space of mitochondria creates an H+ gradient across the mitochondria membrane
Inorganic phosphate is used to convert GDP to GTP
Once G-protein is done activating an enzyme, GTPase removes the phosphate group from GTP, and a kinase gives that phosphate group to ADP to form ATP
A phosphate group is removed from 1,3-biphosphoglycerate and transferred to 2ADP becoming 2ATP; 1,3-biphosphoglycerate becomes 3-phosphoglycerate
In step 10, a phosphate group is removed from 2PEP and transferred to 2ADP becoming 2ATP; 2PEP becomes 2 pyruvate
Total of 4 ATP produced in glycolysis; net production of ATP is 2 ATP for the cycle
The ATP created is through a process called substrate-level phosphorylation: an enzyme reacts w/ a substrate that has a phosphate group, the reaction forms a byproduct and the transfer of the phosphate group to ADP to form ATP
ATP is invested in the first step of glycolysis converting glucose to glucose 6-phosphate
ATP is invested in the third step of glycolysis converting fructose 6-phosphate to fructose 1,6-biphosphate
Total of 2 ATP invested in glycolysis
After starting this sequence of events, cAMP is converted to AMP by phosphodiesterase
cAMP jump starts the signal transduction cascade
Step 2 and Step 3 demonstrate a phosphorylation cascade
At each stage stage of activation, multiple molecules of the protein are activated, amplifying the effect of the signal molecule
Phosphate is taken from ATP (forming ADP)
Activated by an addition of a phosphate group by a previous kinase
- For FACILITATED DIFFUSION, some transmembrane proteins contain a HYDROPHILIC INTERIOR to help transport ions, big/polar molecules in & out of cell
- Carrier Proteins: changes shape for the molecule to bind to & allows it to enter/leave the cell
- Channel Proteins: provides a road for specific molecules to pass through
- Contains nonpolar side chains (hydrophobic) that helps anchor itself to the phospholipid bilayer
- Quaternary Structure
- a dimer of two tertiary structured proteins
- Connected via HYDROGEN BONDS and VAN DER WAALS between the two subunits
- Tertiary Structure
- Bonds depends on the R groups involved
- acidic R group + basic R group = ionic bond
- polar R group + polar R group = polar bonds (hydrogen bonds)
- Only covalent bond present is DISULFIDE BONDS
- nonpolar R group + nonpolar R group = nonpolar (hydrophobic interactions)
- nonpolar R groups are "folded" into the protein away from water
- Secondary Structure
- Forms ALPHA helices and BETA pleated sheets
- Connected via HYDROGEN BONDS between MAIN CHAINS
- Primary Structure
- Connected via PEPTIDE BONDS
- Hydrophilic (polar) head face outside toward water around cells
- Hydrophobic (nonpolar) tails face inside away from water around cells
- Cholesterol
- only found in animal cells
- dampens effects of temperature on cells making it where membranes aren't as susceptible to cold temperatures
- works as a buffer preventing cold temperatures from inhibiting fluidity and warmer temperatures from increasing fluidity too much
- Unsaturated
- fewer bound hydrogen atoms
- adjacent carbon atoms in the hydrocarbon tails bond together
- angle forms in tails because of the carbon atoms bonding together; tails no longer straight
- decreasing temperature does not compress the tails because of their shape so molecules are still able to squeeze through the membrane; high fluidity
- Saturated
- no double bonds between adjacent carbon atoms
- saturated with bound hydrogen atoms
- relatively straight hydrophobic hydrocarbon tails
- decreasing temperature "solidifies" membrane as the tails are compressed together; makes for low membrane fluidity
- It is responsible for the protection of the cell and it selects what comes in and out of the cell.
- It consists of a phospholipid bilayer, which has phospholipids and proteins.
- Vacuoles (Membranous Sac)
- Central Vacuole
- It is a storage of inorganic ions in plant cells (Potassium and Chloride). Also plays a role in plant growth.
- Contractile Vacuoles
- Helps pump excess water out freshwater protists cell
- Food vacuole
- Formed by phagocytosis when a cell stores food.
- Lysosomes
- It uses enzymes to digest macromolecules by hydrolyzation. To digest food, a process called phagocytosis used.
- It is a membranous sac full of enzymes such as nucleases, proteases, lipases, etc.
M
- Modifies, stores and routes the products of the endoplasmic reticulum.
- Consist of flat membranous sacs called cisternae.
- Endoplasmic Reticulum
- Rough ER
- It helps fold proteins
- Has a rough surface due to the ribosomes all over it.
- Smooth ER
- It synthesizes lipids, metabolizes carbohydrates, detoxifies drugs and poisons, and stores calcium ions.
- Has a smooth outer surface, free of ribosomes.
N
- Regulates the traffic of proteins and RNA through its pores.
- Consists of a double membrane that has that has a continuous inner and outer membrane with pore structures in it.
- Help carry out protein synthesis by translating mRNA.
- It consist of ribosomal RNA and proteins.
- Gives support to the cell and maintain its shape.
- Consists of microtubules, microfilaments and intermediate filaments
- Removes hydrogen atoms form certain molecules and adds them to oxygen, creating hydrogen peroxide.
- Consist of enzymes that make hydrogen peroxide.
- Controls the activity of the cell and directs protein synthesis.
- Consists of DNA which is made of chromosomes. Chromosomes consist of chromatin.
- Uses oxygen to produce ATP for the entire cell
- Consist of a outer membrane and inner membrane that has cristae. Also has mitochondrial matrix which has ribosomes and DNA.
- Animal Cell Junctions
- Gap Junctions
- Provides channels filled with cytoplasm from one cell to the adjacent cell so molecules can pass.
- Consist of membrane proteins
- Desmosomes
- Fastens cells together into strong sheets. For example, it attaches muscle cells to one another.
- Filaments made up of keratin proteins anchor desmosomes into cytoplasm.
- Tight Junction
- Prevents fluid from moving across a layer of cells.
- The plasma membrane of two cells use specific proteins to press tightly against each other.
- Centrosomes
- Organizes microtubules which helps organize the cytoskeleton.
- Consist of two centrioles which are consisted of microtubules.
- Extracellular Matrix (ECM)
- Regulates the cells behavior by attaching to integrins (which are membrane proteins) allowing it to send signals throughout the cell.
- The ECM consist of proteoglycans, polysaccharides, and glycoproteins such as collagen and fibronectin.
- Plasmodesmata
- Channels that allows molecules to pass between adjacent plant cells.
- They are membraned lined channels filled with cytosol.
- Chloroplast
- Converts sunlight energy into stored energy in sugar.
- Consist of granum (stack of thylakoids) inside a membrane sack with ribosomes.
- The cell wall provides structure and support for a plant cell.
- The cell wall is has a primary cell wall, secondary cell wall, and middle lamela.
- Protects the cell from outside threats
- The glycocalyx is mainly made up of polysaccharides and/or peptides
- The bacterial chromosome helps to store and transmit biological information to other cells. Its role also includes replicating, transcribing, and translating to form DNA, RNA, and protein.
- Bacterial chromosomes consist of DNA, RNA, and an assortment of proteins
- Encloses the cytoplasm. The primary function of the plasma membrane is to protect the cell from its surroundings. The plasma membrane also has selective permeability, which allows it to decide what can go through it
- The fimbriae is a type of appendage of prokaryotic cells. It allows for prokaryotes to stick to surfaces and to other prokaryotes (due to their hair-like protrusions)
- The plasma membrane is made up of the phospholipid bilayer, which contains phospholipids and proteins.
- Ribosomes main job is to translate messenger RNA to protein (protein synthesis)
- Ribosomes in prokaryotes are mostly made up of ribosomal proteins and ribosomal RNA
- The nucleoid is the region where a cell's DNA is located. It also plays an essential role in controlling the activity of the cell
- The nucleoid seems to be composed of mainly DNA and some RNA as well
- The flagella is responsible for the cell's motility and movement
- The flagellum is made up of three structures; the basal body, the hook, and the filament. The flagellum also consists of protein flagellin
- Function:
- The cell wall provides structure to the cell and protects the plasma membrane by filtering what goes in and out
- Composed of:
- The main component that makes up the cell wall is peptidoglycan, which gives the cell its shape and surrounds the cytoplasmic membrane
