BIOLOGY PRACTICE TEST -2

Click below for multiple choice questions.

1. Polymerase chain reaction: Quiz 1

2. Active Transport: Quiz 2

3. Endocytosis/exocytosis: Quiz 3

4. Electron Transport Chain/ATP Production: Quiz 4

5. Electron Transport Chain/ATP Production: Quiz 5

6. Energy Conversion: Quiz 6

7. Photosynthesis: Quiz 7

8. Mitosis: Quiz 8

9. Meiosis: Quiz 9

BIOLOGY PRACTICE TEST-1

Click below for multiple choice questions:

1. Catalysis: Quiz 1

2. DNA Structure: Quiz 2

3. DNA Packaging: Quiz 3

4. DNA replication: Quiz 4

5. Transcription: Quiz 5

6. Translation: Quiz 6

7. Polyribosome: Quiz 7

8. Mutation: Quiz 8

9. DNA Repair: Quiz 9

10. Feedback inhibition: Quiz 10

CHEMISTRY PRACTICE QUESTIONS FOR THE DAY

Click below for multiple choice questions.

1. Atomic Structue: Practice Quiz 1

2. Covalent Bond: Practice Quiz 2

3. Ionic Bond: Practice Quiz 3

4. Diffusion: Practice Quiz 4

5. Osmosis: Practice Quiz 5 

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PROTEIN SYNTHESIS

STEP 1: Transcription of mRNA from a DNA gene 

• mRNA stands for messenger RNA. 
• Protein synthesis begins with the transcription of mRNA from a DNA gene in the nucleus.
•  The RNAs then migrate from the nucleus into the cytoplasm. 
• Prior to the beginning of the protein synthesis, all of the component parts are assembled in the ribosomes. 

STEP 2: Initiation

• In the cytoplasm, protein synthesis is actually initiated by the AUG codon on mRNA. 
• The AUG codon signals both the interaction of the ribosome with m-RNA and also the tRNA with the anticodons (UAC). The AUG codon is known as the start codon. This is the codon for the amino acid, methionine.
• The ribosome moves along the mRNA to read the next codon. Once this is done, a tRNA (transfer RNA) with an anticodon approaches the mRNA. This tRNA carries along with it the corresponding amino acid. 
• The next process is to start growing peptide chain by having amine bond to the carboxyl acid group of methionine in order to elongate the peptide.

STEP 3: Elongation:

Elongation of the peptide begins as various tRNA's read the next codon. The tRNA with the anticodon brings along the corresponding amino acid and a peptide bond is formed between the amino acids. The previous tRNA then returns into the cytoplasm to be reused. The whole process is then repeated.

STEP 4: Elongation and Termination:

• When the stop signal on mRNA is reached, the protein synthesis is terminated. The stop codons are UAA, UAG, and UGA. The last amino acid is hydrolyzed from its t-RNA.
• The peptide chain leaves the ribosome. The N-formyl-methionine that was used to initiate the protein synthesis is also hydrolyzed from the completed peptide at this time.
• The ribosome is now ready to repeat the synthesis several more times.

REPRODUCTION IN ANIMALS

Gametes refers to the sperm and the egg. During sexual reproduction, the sperm and the egg unite to form the zygote.
                           Zygote = sperm + egg

Each gamete has half the normal complement of chromosomes, that is, 23 chromosomes in each gamete. The gametes are said to be monoploids (haploid). Fusion results in the full number of chromosomes, 46 (23 pairs). The zygote is referred to as diploid.

In the male, the external reproductive organs are the penis and scrotum.
The internal organs consist of:

• The testis which contains the seminiferous tubules, where the sperms are produced.
• The interstitial cells produce testoterone, the male sex hormones.
• The sperm travels in the epididymis, the coiled tubules, into the vas deferens to the ejaculatory duct to the urethra.
• Seminal vesicles produce seminal fluid that carries the sperms.
• Prostate produces prostatic fluid that also carries the sperms.

In the female, the primary reproductive organs are the ovaries, fallopian tubes and uterus.

• Ovaries produce the eggs and the hormones, estrogen and progesterone.
• Immature egg is called oocyte.
• Matured egg is released during ovulation.
• The egg travels in the fallopian tubes, where it can be fertilized by the sperm. Note that the fertilized egg begins to divide within the tubes within few hours of conception.
• The lining of the uterus is called the endometrium.
• The fertilized egg implants in the endometrium.
• The fetus obtains nourishment via the placenta. Note that, the fetal and maternal blood do not have direct connections. Exchange of nutrients and oxygen is by diffusion.
• The fetus is connected to the placenta via the umbilical cord.
• The fetus is covered by the following membranes: amnion and chorion.
• If there is no fertilization, the uterus sheds its, endometrium. This is referred to as menstruation.

CONDITIONED REFLEX

Under classical conditioned reflex,  the learned response to the previously neutral stimulus the conditioned response is. For example, the smell of food naturally elicits the feeling of hunger. If a whistle is blown any time food is presented, the sound of the whistle gets associated with the food. It gets to a time when you naturally get hungry any time  the whistle is blown without the physical presence of food. The smell of food is the unconditioned stimulus. The feeling of hunger in response to the the smell is the unconditioned response and the sound of the whistle is the conditioned stimulus. The conditioned response would be feeling hungry when you hear the sound of the whistle.

More examples of conditioned reflex:
1. A child who receives an injection from a person in white coat may associate any white coat with the pain of injection. Any time the child see a person in white coat, he/she suddenly develops fear and avoidance reaction.

2. John and Mercy, who are students, are in love with each other but they attend schools several mile apart. During the spring and summer breaks, they spend time together picking grapes. When they get back to their schools John experiences the feeling of happiness any time he sees grapes.