Molecular Biology of Genetic Material and Gene Expression

A set of flashcards covering DNA experiments, structure, replication, transcription, and translation based on the lecture transcript.

What happened when Griffith injected a mixture of heat-killed virulent and live non-virulent bacteria into mice?

The mice died, and live virulent bacteria were isolated from them.

What is the process by which foreign DNA is introduced into a bacterial cell?

Transformation

Who first identified DNA in 1869?

Friedrich Miescher

In the 1944 experiment by Avery and his colleagues, which component of heat-killed virulent bacteria was able to transform non-virulent bacteria?

Only the DNA fraction

In the 1952 Hershey and Chase experiment, which radioactive isotope was used to label the DNA core of bacteriophages?

Radioactive phosphorus ($P$)

What was the conclusion of the Hershey and Chase experiment regarding the genetic material of phages?

DNA, not protein, entered the bacteria and carried the genetic information.

What is the process of genetic material transfer from one bacterium to another via a virus?

Transduction

What structural model did Watson and Crick propose in 1953?

The double helix model of DNA structure

How is conjugation defined in bacterial genetic transfer?

A process of genetic material transfer between bacterial cells through direct cell-to-cell contact, typically involving a pilus.

According to Chargaff's rules, what are the base pairing assignments?

Adenine pairs with thymine ($A-T$) and guanine pairs with cytosine ($G-C$).

What are the three parts of a nucleotide?

A phosphate group, a five carbon sugar, and a nitrogenous base.

What is the difference between a nucleoside and a nucleotide?

A nucleoside consists of a sugar and a base; a nucleotide is a nucleoside with one or more phosphate groups attached.

Which nitrogenous bases are classified as purines?

Adenine and guanine, double-ringed structure

Which nitrogenous bases are classified as pyrimidines?

Cytosine, thymine (in DNA), and uracil (in RNA). Single ringed structure

What are the differences between the sugars and nitrogenous bases in DNA versus RNA?

DNA contains deoxyribose and thymine ($T$), while RNA contains ribose and uracil ($U$).

In what orientation do the two strands of a DNA double helix run?

Antiparallel (opposite directions)

How many hydrogen bonds hold the $G-C$ base pair together compared to the $A-T$ base pair?

The $G-C$ pair has three hydrogen bonds, while the $A-T$ pair has two.

In which direction are DNA and RNA strands always read? In which direction are they always built?

They are read 3’ to 5’ by enzymes that copy/translate them, new strands are always built 5’ to 3’

When during the cell cycle is DNA replicated?

During the $S$ phase (synthesis phase).

What is the name of the specific site where replication begins in bacteria?

The origin of replication ($ori$)

Why do eukaryotic chromosomes have multiple origins of replication?

Because they are larger and linear, multiple origins allow them to replicate their extensive genomes efficiently.

What is the role of the template strand during DNA replication?

It serves as a pattern for the synthesis of a new complementary DNA strand during replication

Distinguish between the leading and lagging strands during replication.

The leading strand is synthesized continuously following the replication fork. while the lagging strand is synthesized discontinuously in short fragments, but in the opposite direction of the replication fork

What are Okazaki fragments?

Short segments of newly synthesized DNA formed on the lagging strand.

What is the primary function of telomeres at the ends of eukaryotic chromosomes?

Telomeres: repetitive sequence of DNA located at the ends of eukaryotic chromosomes. To protect coding regions from degradation and prevent chromosomes from fusing with each other.

State the Central Dogma of biology.

Genetic information flows from DNA to RNA and then to protein. Process is essential to know how genes are expressed

In gene structure, what is the purpose of the promoter region?

It signals where transcription should begin and acts as a binding site for RNA polymerase. It’s Located near the beginning of a gene

What is RNA polymerase?

Enzyme that carries out transcription, and helps to position the enzyme correctly to start the process

What is the start site?

Exact nucleotide on the DNA where transcription begins

After the Promoter, what is the Coding sequence?

It contains the instructions for building a protein

What is the difference between introns and exons?

Introns are non-coding regions removed during RNA processing, while exons are the coding parts that are expressed.

What is the sense strand?

Aka coding strand, has a sequence that is similar to the mRNA that will be produced with Uracil in RNA. It serves as genetic code format

What is Antisense strand?

Aka Non coding, aka template strand, is complementary to the sense strand and is the strand the is actually ready by RNA polymerase during transcription to synthesize mRNA

What is a codon?

A sequence of three consecutive nucleotides in DNA or RNA that specifies a particular amino acid or a start/stop signal.

What direction does transcription go? Which strand of DNA is read?

Proceeds in 5’ to 3’ along the template strand

How many RNA polymerases are there in Bacteria?

One type

How many main types of RNA are found in bacteria?

Three (messenger: carries genetic code from DNA to the ribosome serving as a template for protein synthesis, transfer: molecules bring specific amino acids to the ribosome to be added to the growing polypeptide chain during translation, and ribosomal: structural component of ribosomes, machinery responsible for protein synthesis. RNA).

What is the role of transfer RNA (tRNA) in translation?

It brings specific amino acids to the ribosome to be added to the growing polypeptide chain.

What is RNA processing in eukaryotes and provide three processing steps

“Modifications that occur to a newly synthesized RNA molecule before it becomes functional.

Step 1: 5’ capping: modified guanine is affected to the 5’ end of the mRNA

Step 2: 3’ polyadenylation: tail of adenine nucleotides is added to 3’ of mRNA

Step 3: Splicing: introns are removed from pre-mRNA and exons are joined together

Translation

Process of synthesizing proteins from mRNA, occurs in cytoplasm of cell, with organelle ribosome

Where in the cell does translation occur?

In the cytoplasm.

What is the structure of tRNA?

Cloverleaf shaper due to base pairing within molecule, which folds into L shape

Where does an amino acid bind to on a tRNA molecule?

At the $3'$ end, specifically at the acceptor stem.

What is the anticodon for tRNA?

Anticodon is a loop that contains a sequence of three nucleotides that is complementary to a specific codon for mRNA

What is the universal start codon and which amino acid does it specify?

$AUG$, specifying Methionine.

What are the three tRNA binding sites in a ribosome?

The $A$ site (aminoacyl), binding incoming tRNA carrying the amino acid, the $P$ site (peptidyl), holds the tRNA carrying the growing polypeptide chain, and the $E$ site, releases uncharged tRNA after it has delivered amino acid (exit).

What is the function of chaperone proteins?

They help nascent polypeptide chains fold correctly into 3D structures and prevent misfolding or aggregation.

What system is responsible for identifying and destroying old or damaged proteins?

The ubiquitin-proteasome system.

Transcription

Process of which a cell makes a RNA copy of a specific segment of DNA, acting as a blueprint for building proteins. Vital step in gene expression