How do you know whether to use avere or essere as an auxiliary verb when conjugating in the past tense?
One way to look at this is to determine whether the verb is transitive or intransitive. Transitive verbs require a direct object, for example I drive my car. In this case, the direct object that the verb is referring to is 'my car'. In these cases, the verb avere will be used when this sentence is converted into the past tense. Therefore, in italian the sentence is 'ho guidato il mio veicolo.' Intransitive verbs, on the other hand, don't have an object and rather represent a change of state or movement. For example, 'The door is open'. In this case, essere is used as the auxiliary verb: "La porta è chiusa". Another way to think about it when first learning is that all verbs will use avere for their auxiliary verb and those that use essere are the exception. These are verbs that constitute changes of state or motion. For example, andare, partire, nascere, morire.
What is the difference between reinforcement and punishment?
The goal of reinforcement is to encourage a behavior whereas the goal of punishment is to discourage a behavior from continuing. 'Positive' and 'negative' are used to describe the type of reinforcement and punishment, but not to refer to a positive or negative behavior. The positive and negative simply refers to whether something is given to a person or taken away in order to encourage (reinforcement) or discourage (punishment) a behavior. Positive reinforcement is when something is given to continue a behavior. For example, giving a sticker to a student when they complete their assignment. Negative reinforcement is when something is taken away to continue a behavior. For example, taking away homework for a night from a student who has completed 10 assignments in a row. In both of these cases, the behavior of completing assignments is reinforced. Positive punishment is when something is given to someone to stop a behavior. For example, giving a speeding ticket to a driver. Negative punishment is when something is taken away from an individual to stop a behavior. For example, taking away the driver's license from the speeding driver. In both cases, the punishments are aiming to stop the driver from speeding in the future.
How does a messenger RNA molecule get translated by a ribosome into a primary amino acid sequence in a eukaryotic cell?
In brief, the mRNA molecule is first made from DNA in the nucleus of a eukaryotic cell. The mature mRNA molecule travels to the cytoplasm where it will get recognized by the small ribosomal subunit. The ribosomal subunit with the help of proteins called initiation factors find the start codon that codes for the amino acid methionine. A codon is a 3-base pair long sequence on the mRNA molecule. The codon for methionine is AUG. Once the codon is found, the initiation factors fall off and allow for the large ribosomal subunit to attach. Molecules called tRNAs have two main parts to point out for our purposes. (1) the anti-codon sequence that will bind complementary to the codon on the mRNA molecule and (2) the amino acid that is associated with the anti-codon/codon is attached to the 5' end of the tRNA molecule. The correct tRNA molecule enter the A site of the large ribosomal subunit and attaches to the codon. As it moves over into the next site, the P site, another tRNA binds to the next codon. The amino acids on the ends of the tRNA molecules form a peptide bond as the second tRNA molecule moves to the P site. At the same time, the first tRNA molecule moves to the E site and exits the ribosome, falling off of the mRNA molecule. This continues until a stop codon is reached. The ribosome subunits will fall off the mRNA molecule and the cell is left with a primary amino acid sequence.