Ch 1 - Overview of Genome Transmission and Expression

What is the central dogma of molecular biology?

DNA (information, also involves replication and repair within), transcription to RNA (decoding), translation to protein (work)

What describes the flow of genetic information?

Unidirectional, but there are exceptions we will learn about

What does DNA stand for?

Deoxyribonucleic acid

In what manner does DNA store genetic information?

In a stable heritable form

What is a nucleotide

A complete building block of DNA or RNA: sugar + phosphate group + nitrogenous base

How many nucleotides does DNA have

Four

What is a base

One part of a nucleotide: guanosine, adenosine, thymidine, cytidine

What carries the information “code” in DNA

The linear sequence of nucleotides

Pairing pattern

A and T, C and G

Orientation of the DNA stands

Anti-parallel. A base on the 5’ end of one strand is complementary to a base of the 3’ end of the other strand.

What happens to information in DNA before it is transmitted?

It is replicated

What suggested a possible copying mechanism for DNA?

The specific pairing

Steps for DNA replication

Original strands (gray) are separated. New DNA strands (green) are synthesized in an anti-parallel manner (5’ to 3’ direction) by DNA Polymerase using the old DNA strands as templates. Nucleotides are added in a complementary manner– A pairing with T and C pairing with G. Two identical double-stranded (ds) DNA molecules are produced from one original molecule.

What do replicated chromosomes do in cell division?

They segregate

How are copied chromosomes held and why?

They are held together, this helps chromosomes segregate accurately

What are key components of the transmission of the genome between generations or between cells?

Accurate copying (replication) of information. Correct separation (segregation) of copies. Transfer of copies into new cells created by division of the original cell. Each step has several safety nets and checkpoints.

Which two processes express the genome?

Transcription and translation

Transcription

Copying the sequence of a segment of DNA into an RNA molecule (ribonucleuic acid)

How is the RNA made from transcription used?

Directly by the cell (biological function) or as an information template to direct synthesis of a particular protein (translation). A gene is a segment of DNA that codes for a protein or functional RNA molecule.

What are the steps of transcription?

RNA polymerase uses one strand of DNA as a template to synthesize a complementary RNA strand. RNA contains uracil (U) instead of thymine (T); uracil pairs with adenine (A). Specific DNA sequences instruct RNA polymerase where to start and to stop transcribing. The RNA produced is the primary transcript, which is processed into the final RNA product. Resulting strand is anti-parallel.The enzyme reads the DNA in the 3’ to 5’ direction, so the growing RNA strand is the in the 5’ to 3’ direction.

Several types of RNAs exist but which three are central to the expression of the genome into proteins?

Messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA)

Messenger RNA

Carries the sequence encoding a protein and acts as the template for translation

Transfer RNA

Acts as an adapter that "reads" the mRNA and brings the encoded amino acids for protein synthesis

Ribosomal RNA

Together with ~100 proteins, from ribosomes (protein synthesis factories where translation occurs)

What does the translation of mRNA involve?

Decoding and synthesizing it into a protein

What are proteins synthesized from?

20 different amino acids, therefore has tremendous potential for variation in structure and function

What do proteins do?

Carry out most cellular functions (like structural and catalytic)

Range of proteins

A few amino acids long (calmodulin) to many thousands (hemaglutinin) - typically 100-1000 amino acids in length

What may proteins contain?

Distinct separate proteins that come together to form a functional unit

What translates the mRNA?

Special RNAs (tRNA and rRNA)

Codon

Triplets of nucleotides in the mRNA

How does tRNA decode?

Recognizes each codon in order from 5' to 3' and bringing its cognate amino acid to be joined with the next amino acid, and so on

Ribosome

The translation "machine" that holds everything in place

Codon ambiguity rule

Each codon codes for one amino acid, but each amino acid can have multiple codons

Start of translation

AUG codon, so most proteins begin with the amino acid methionine (but methionine can occur inside the sequence as well)

Prokaryote cellular structure

Do not have internal membrane-bound compartments (like a nucleus). And are unicellular.

Transcription and translation exception

Can occur simultaneously in prokaryotes only. A ribosome attaches to a messenger RNA strand to build a protein while that RNA is still being copied from DNA.

Poly-cistronic

Transcripts may be poly-cistronic, more than one gene per RNA transcript

Eukaryotic cellular structure

Membrane-bound organelles

Where are chromosomes found

In nucleus

Where do replication and transcription occur

In the nucleus

Where does translation occur

In the cytoplasm within ribosomes, so mRNA must be exported to the cytoplasm for translation. So, transcription and translation cannot be simultaneous.

Types of mutations

Point mutations (small and single nucleotide changes) and insertions, rearrangements, and deletions (range in size from small to very large)

What can mutations effect?

Sequence and structure of a protein. Regulatory regions of a gene and change expression.

Null/loss-of-function mutations

Mutations that eliminate the function of a gene

Types of point mutations

Missense, nonsense, silent

Missense mutations

Alter the encoded amino acid, might cause trouble

Nonsense mutations

Introduce a premature stop codon, usually bad

Silent mutations

Do no change the amino acid sequence, no effect