genetics short answer

What are the different parts of a nucleotide? How does an RNA nucleotide differ from a DNA nucleotide?

sugar, phosphate, nitrogenous base.

DNA nucleotide: Contains deoxyribose sugar and uses the base thymine (T).

RNA nucleotide: Contains ribose sugar and uses the base uracil (U) instead of thymine.

What is a base pair? What is a base?

Base: A nitrogen-containing molecule in a nucleotide that stores genetic information. The bases are adenine (A), thymine (T), cytosine (C), guanine (G) in DNA and uracil (U) in RNA.

Base Pair: Two complementary bases that are held together by hydrogen bonds in DNA. A pairs with T and C pairs with G.

Compare and contrast DNA and RNA.

Similarities:

• Both are nucleic acids made of nucleotides.

• Both contain a sugar, phosphate group, and nitrogenous bases.

• Both store and use genetic information.

Differences:

DNA	RNA
Double-stranded	Usually single-stranded
Contains deoxyribose sugar	Contains ribose sugar
Uses thymine (T)	Uses uracil (U)
Stores long-term genetic information	Helps use genetic information to make proteins
More stable	Less stable

What is complementary base pairing? How is it used in replication, transcription, and translation?

Complementary Base Pairing: The rule that specific nitrogenous bases pair together using hydrogen bonds:

• DNA: A pairs with T, and C pairs with G

• RNA: A pairs with U, and C pairs with G

How it is used:

• Replication: DNA uses complementary base pairing to make an exact copy of itself. Each original DNA strand acts as a template for a new matching strand.

• Transcription: DNA uses complementary base pairing to create an mRNA strand. RNA bases pair with the DNA template (A → U, T → A, C → G, G → C).

• Translation: The mRNA codons use complementary base pairing with tRNA anticodons to bring the correct amino acids and build a protein.

How is DNA replicated? Compare replication of the leading strand to the lagging strand.

DNA Replication: The process of copying DNA to make an identical DNA molecule before a cell divides. It is semiconservative, meaning each new DNA molecule contains one original strand and one newly made strand.

Steps:

1. Helicase unwinds and separates the DNA strands by breaking hydrogen bonds.

2. Primase adds RNA primers to start replication.

3. DNA polymerase adds complementary nucleotides to build new DNA strands.

4. Ligase connects DNA fragments together.

Leading vs. Lagging Strand:

Leading Strand	Lagging Strand
Made continuously	Made discontinuously
DNA polymerase moves toward the replication fork	DNA polymerase works away from the replication fork
Requires one RNA primer	Requires many RNA primers
Produces one continuous strand	Produces Okazaki fragments that are joined by ligase

Why they differ: DNA polymerase can only build DNA in the 5’ → 3’ direction, so the two antiparallel DNA strands must be copied differently.

Name and describe the 6 enzymes/proteins used in DNA replication

1. Helicase – Unwinds and separates the two DNA strands by breaking hydrogen bonds between bases.

2. Topoisomerase (DNA gyrase in bacteria) – Relieves tension and twisting ahead of the replication fork caused by DNA unwinding.

3. Primase – Makes short RNA primers that provide a starting point for DNA polymerase.

4. DNA Polymerase – Adds new DNA nucleotides to build the new strand in the 5’ → 3’ direction and proofreads for mistakes.

5. DNA Polymerase I (or RNase H in some organisms) – Removes the RNA primers and replaces them with DNA.

6. DNA Ligase – Seals gaps between DNA fragments by joining Okazaki fragments together on the lagging strand.

Why is the lagging strand replicated discontinuously? (Hint: Think about the enzymes involved.)

The lagging strand is replicated discontinuously because DNA polymerase can only add nucleotides in the 5’ → 3’ direction. Since the two DNA strands are antiparallel, the lagging strand runs in the opposite direction from the replication fork.

As a result, primase must add multiple RNA primers, allowing DNA polymerase to make short sections called Okazaki fragments. DNA ligase then joins these fragments together to form a continuous strand.

What is the difference between the leading strand and the leading strand template? The lagging strand and the
lagging strand template?

Leading Strand vs. Leading Strand Template:

• Leading Strand: The new DNA strand being made continuously by DNA polymerase in the 5’ → 3’ direction.

• Leading Strand Template: The original DNA strand that DNA polymerase reads to build the new leading strand.

Lagging Strand vs. Lagging Strand Template:

• Lagging Strand: The new DNA strand made discontinuously in short pieces called Okazaki fragments.

• Lagging Strand Template: The original DNA strand that is read to create the lagging strand.

Simple way to remember:

• Template = old DNA strand being copied

• Leading/Lagging strand = new DNA strand being built

Compare and contrast RNA polymerase to DNA polymerase

RNA Polymerase	DNA Polymerase
Makes RNA from a DNA template during transcription	Makes DNA from a DNA template during replication
Uses RNA nucleotides (A, U, C, G)	Uses DNA nucleotides (A, T, C, G)
Does not require a primer to start	Requires a primer to start
Produces a single-stranded RNA molecule	Produces a double-stranded DNA molecule
Less proofreading ability	Has stronger proofreading ability

Similarities:

• Both are enzymes.

• Both use a DNA template strand.

• Both build new nucleic acids in the 5’ → 3’ direction by adding complementary nucleotides.

Describe the process of transcription.

1. 1. RNA polymerase binds to the promoter region of DNA.

2. 2. DNA unwinds, exposing one DNA strand to use as a template.

3. 3. RNA polymerase adds complementary RNA nucleotides to build an mRNA strand (A pairs with U, C pairs with G).

4. 4. When RNA polymerase reaches a termination signal, the mRNA strand is released.

5. 5. The mRNA leaves the nucleus (in eukaryotes) and travels to the ribosome for translation.

Simple summary:
DNA → transcription → mRNA → translation → protein.

What is splicing

The process of removing introns (non-coding sections) from pre-mRNA and joining exons (coding sections) together to create a mature mRNA molecule that can be used to make a protein.

Describe the process of translation

Steps:

1. mRNA attaches to a ribosome.

2. The ribosome reads the mRNA codons (3-base sequences).

3. tRNA brings the correct amino acids using its anticodon that matches the mRNA codon.

4. The ribosome joins amino acids together with peptide bonds to form a protein.

5. When the ribosome reaches a stop codon, translation ends and the protein is released.

Roles of RNA:

• mRNA: Carries the genetic instructions from DNA to the ribosome.

• tRNA: Brings amino acids to the ribosome.

• rRNA: Makes up part of the ribosome and helps build proteins.

Simple summary:
DNA → transcription → mRNA → translation → protein.

Name and describe the functions of the three types of RNA needed for translation.

The three types of RNA needed for translation:

1. mRNA (Messenger RNA)

   • Carries the genetic instructions from DNA to the ribosome.

   • Contains codons that tell the cell which amino acids to add.

2. tRNA (Transfer RNA)

   • Brings the correct amino acids to the ribosome.

   • Contains an anticodon that matches the mRNA codon to ensure the correct amino acid is added.

3. rRNA (Ribosomal RNA)

   • Makes up part of the ribosome.

   • Helps hold mRNA and tRNA in place and helps form peptide bonds between amino acids.

Simple summary:

• mRNA = message (instructions)

• tRNA = transporter (brings amino acids)

• rRNA = ribosome (builds the protein)

How do the processes of replication, transcription, and translation differ between a prokaryote and eukaryote?
(Hint: Think about where each of these processes occurs.)

Process	Prokaryotes	Eukaryotes
Replication	Occurs in the cytoplasm because there is no nucleus. DNA is copied before cell division.	Occurs in the nucleus where DNA is copied before cell division.
Transcription	Occurs in the cytoplasm. mRNA is made directly from DNA.	Occurs in the nucleus. mRNA is made from DNA and then processed (splicing) before leaving the nucleus.
Translation	Occurs in the cytoplasm on ribosomes. Translation can begin while transcription is still happening.	Occurs in the cytoplasm on ribosomes after processed mRNA leaves the nucleus.

Simple summary:

• Prokaryotes: No nucleus → replication and transcription happen in the cytoplasm, and translation can happen immediately.

• Eukaryotes: Have a nucleus → replication and transcription happen in the nucleus, while translation happens in the cytoplasm.

Compare and contrast conjugation, transduction, and transformation

Process	Description	How DNA is Transferred
Conjugation	Direct transfer of DNA from one bacterial cell to another	A donor cell uses a pilus to connect to a recipient cell and transfers a plasmid (often through a sex pilus).
Transduction	Transfer of bacterial DNA using a virus	A bacteriophage accidentally carries bacterial DNA from one cell and injects it into another cell.
Transformation	Uptake of free DNA from the environment	A competent cell takes in naked DNA released from dead bacteria.

Similarities:

• All involve the movement of DNA between bacteria.

• All can introduce new traits, such as antibiotic resistance.

• All are examples of horizontal/lateral gene transfer.

Simple way to remember:

• Conjugation = connection (cell-to-cell contact)

• Transduction = virus transfers DNA

• Transformation = taking up DNA from the environment