Test 3 Biology

What is cell differentiation?

Definition: The developmental process where unspecialized cells become specialized in form and function (e.g., skin cells vs. brain cells).

How it works: All cells in a multicelled body have the exact same DNA. Differentiation happens because cells start using different subsets of their DNA while turning off the rest.

 Is differentiation reversible? For example, could a liver cell revert back to a stem cell?

No, it is usually a one-way path. Once a cell specializes (like a liver or muscle cell), most of its DNA is permanently turned off, and its descendants will also be specialized. 

In the Hershey-Chase experiments, why was phosphorus and sulfur used? Why were those chemicals used to figure out if protein or DNA was the transformative molecule?

Sulfur: Found only in proteins (not DNA), so it was used to track viral protein.

Phosphorus: Found only in DNA (not proteins), so it was used to track viral DNA.

Result: Only radioactive phosphorus entered the bacteria during infection, proving definitively that DNA is the molecule of heredity.

What were two things Chargaff postulated about the structure of DNA. How is it similar across species? In what ways can it differ? 

1. The amount of Adenine equals Thymine (A=T), and Guanine equals Cytosine

 (G=C).

1. The proportion of A-T vs. G-C varies between different species.

How it is similar: All DNA uses the same base-pairing rules (A pairs with T, G with C).

How it differs: The DNA sequence (the exact order of bases along the strand) varies tremendously among species and individuals.

What differs between species? The amount of DNA? Whether it is single or double helix? The type of sugar or phosphate in the nucleotides? (hint: its two of these things)

From the text: The amount of DNA (base content/ratios) and the DNA sequence (order of bases) vary among species. (Sugars, phosphates, and the double-helix structure are universal across all DNA).

(2 questions deal with this)  What are the base pairing rules? In other words, which bases pair with which when making a double strand of DNA?

A pairs with T (Adenine with Thymine)

G pairs with C (Guanine with Cytosine)

Where would you find covalent bonds in a DNA molecule? Where would you find hydrogen bonds?

Covalent bonds: Found along the sugar-phosphate backbone, linking the sugar of one nucleotide to the phosphate group of the next.

Hydrogen bonds: Found in the center, linking paired nitrogenous bases together to hold the two strands of the double helix.

(2 questions deal with this)  Describe where you would find the sugar-phosphate backbone and where you would find the nitrogenous base pairs in DNA. Which part is like the “rungs” of a ladder you would step on?

Backbone: Located on the outside of the helix (forming the sides of the ladder).

Nitrogenous base pairs: Located on the inside (forming the "rungs" or steps of the ladder that you would step on).

 Describe briefly how x-ray crystallography works.

X-rays are directed through a purified, crystallized substance.

The atoms scatter the X-rays into a specific pattern, which is captured as an image.

Researchers use this pattern to calculate the size, shape, and spacing of repeating molecular elements (like DNA's width and twist).

What happens to the chromosome number in mitosis? E.g. do daughter cells have half as many, twice as many, the same..

The chromosome number stays the same. The two daughter cells have the same number of chromosomes as the parent cell. 

 Briefly describe G1, mitosis, S phase, G2, and cytokinesis. What order do they go in?

G1: The cell grows and makes the molecules it needs.

S phase: The cell copies its DNA.

G2: The cell prepares for division.

Mitosis: The nucleus divides, and the chromosomes separate into two new nuclei.

Cytokinesis: The cytoplasm divides, forming two daughter cells.

Order: G1 → S phase → G2 → Mitosis → Cytokinesis. 

What is the difference between a benign and malignant tumor?

A benign tumor is harmless and stays in its original tissue. A malignant tumor is dangerous because its cells can spread to other parts of the body. 

What is an oncogene?

An oncogene is a gene with a mutation that causes a cell to divide when it should not, which can lead to a tumor. 

What separates in anaphase I of meiosis? What separates in anaphase II?

In anaphase I, homologous chromosomes separate. In anaphase II, sister chromatids separate.

What kind of cells are made in meiosis? Are they diploid or haploid? How many daughter cells are produced?

Meiosis produces reproductive cells, such as eggs and sperm. They are haploid, meaning they have one set of chromosomes. Meiosis produces four daughter cells. 

What does asexual reproduction produce?

Asexual reproduction produces offspring from one parent. The offspring are genetically identical to the parent, except for any new mutations.

What suffixes do proteins usually have?

Proteins usually have the suffix -in or -ase.

What are the protein coding sections of DNA called?

The protein-coding sections of DNA are called genes.

(2 questions deal with this) How is transcription different from translation?

Transcription copies DNA into RNA, while translation uses the information in mRNA to build a protein. 

 (2 questions deal with this) What is the role of transfer RNA?

Transfer RNA (tRNA) brings amino acids to the ribosome in the correct order to build a protein. 

 What is the region of DNA where transcription starts called?

The region of DNA where transcription starts is called the promoter.

 In eukaryotes, are introns removed before or after transcription ends? 

Introns are removed after transcription ends, when the new RNA is modified.

 What happens when regulatory proteins bind to the promoter region of DNA?

Regulatory proteins can turn genes on or off by helping RNA polymerase bind to the promoter or preventing it from binding. 

 (2 questions deal with this)  What is the genetic code? What is the difference between a codon and an anti-codon? Which-(or is it both…)- of these is made of only three nucleotides?

The genetic code is the set of 64 codons that provide instructions for making proteins. A codon is a group of three nucleotides on mRNA, while an anticodon is a group of three nucleotides on tRNA that matches with a codon. Both are made of three nucleotides. 

How many amino acids would you find in most organisms?

Most organisms use 20 different amino acids to make proteins.

What would be the amino acid sequence of ATGGCGCTTAGA? Use the provided codon chart:

The amino acid sequence for ATGGCGCTTAGA is:

• DNA: ATG GCG CTT AGA

• mRNA: AUG GCG CUU AGA

• Amino acids: Methionine – Alanine – Leucine – Arginine

Using the above chart, how many codons code for serine?

There are 6 codons that code for serine.

What is the specific name for the bond a ribosome makes between two amino acids?

The bond a ribosome makes between two amino acids is called a peptide bond.

What happens when the ribosome reaches UAA, UAG, or UGA on the mRNA strand?

When the ribosome reaches UAA, UAG, or UGA, translation stops, and the ribosome releases the new polypeptide. 

On what structure would you find an anticodon?

An anticodon is found on transfer RNA (tRNA). 

What would be the likely effect (if any) on the resulting protein if there was a mutation in the intron region of the gene?

A mutation in an intron would likely have no effect on the resulting protein if the intron is removed normally. However, a mutation that affects the intron’s boundaries could interfere with RNA splicing and change the protein. 

 (two questions relate to this) What do homeotic genes control? What product do they make that helps them do this?

Homeotic genes control the development of specific body parts. They make regulatory proteins called transcription factors that help control the expression of other genes. 

What do transcription factors bind to?

Transcription factors bind to specific regulatory sites on DNA.

What are Barr bodies? What chromosomal sex would expect to find them in?

Barr bodies are inactivated, condensed X chromosomes found in the cells of typical XX females. Most genes on the inactivated X chromosome are not expressed.