7 The Blueprint of Life, From DNA to Protein

DNA

Hereditary material that is passed onto offspring

Characteristics of each cell is dictated by information contained within [__]

Genome

Complete set of genetic information

• [__] of all cells is composed of DNA

• gene: functional unit of the [__]; codes for products (protein, RNA)

Genomics

Study of nucleotide sequence

Phenotype

Visible or observable trait of that individual or cell (product of their genotype)

takes form of:

• physical characteristics

• enzymes that perform certain actions inside cell

made possible by expression of genes

Genotype

Genome of the organism that contains all of their genes

DNA replication

1/2 tasks cells must accomplish to multiply

The duplication of genome

• origin of replication: distinct region of DNA molecule where replication is initiated

• melting of double-stranded DNA = breaking of DNA complex apart so that strands can be used as a template for synthesis

  • creates “replication bubble”

  • creates replication forks: site where double helix is unwound to expose single strands that can act as templates; where synthesis is advancing towards

    • “advancing forks”

[__] is bidirectional: goes in both directions

• goes till termination site » DNA molecules go apart and go into new daughter cells

semiconservative

Refers to the model that DNA divides

wherein it contains:

• one original strand of DNA

  • parental strand → template strand

• a newly synthesized DNA strand

RNA primer

Synthesized by enzymes called primases

Initiates the DNA strand for replication; Required by DNA polymerase in order to replicate as it places down a 3’ -OH end

DNA polymerase

Enzyme that carries out DNA replication

Reads and synthesizes only from one direction, (3’ to 5’) and (5’ to 3’) respectively

Can only add nucleotides, not initiate

» MUST be 3’ -OH end in order to add

notice: lagging and leading strands occur as only portions of the newly synthesized strand goes the “right way” for [__]

synthesized strand 5’ to 3’ » leading strand

synthesized strand 3’ to 5’ » lagging strand (has fragments)

Okazaki fragments

Small fragments the lagging strand is synthesized into.

Nucleic acid fragment synthesized as a result of the discontinuous replication of the lagging strand of DNA.

origin of replication

Distinct region of DNA molecule where replication is initiated

How DNA replication works across template strands from the [__] is that:

• RNA primer initiates leading strand synthesis

• as soon as leading strand reaches end of replication fork, RNA primer is placed down on second template strand

• RNA primer initiates lagging strand synthesis

• DNA polymerase finishes synthesis of Okazaki fragments and a different DNA polymerase remove the RNA primer in between the fragments

• gets sealed, and the two synthesized DNA strands look identical

leading strand

Strand that synthesizes continuously (5’ → 3’) as it only has to add on to the 3’ end in the direction that RNA polymerase is used to (3’ to 5’)

synthesizes towards replication fork, away from origin of replication

vs. lagging strand (3’ → 5’) synthesizing in chunks as it has to latch on to parental strand of (5’ to 3’) while only being able to add to 3’-OH

synthesizes away from replication fork, towards origin of replication

lagging strand

Strand that synthesizes in chunks (3’ → 5’) as it has to latch on to parental strand of (5’ to 3’) while only being able to add to 3’-OH

→ must be reinitiated regularly by RNA primer

synthesizes away from replication fork, towards origin of replication

vs. leading strand (5’ → 3’) synthesizing continuously on (3’ to 5’) as it just needs to add on to the 3’ end in the direction RNA polymerase is used to

synthesizes towards replication fork, away from origin of replication

Gene expression

2/2 tasks cells must accomplish to multiply

The transcription and translation of DNA information to produce the encoded product

DNA —transcription→ RNA —translation→ protein

central dogma

The [__] of molecular biology is that information flows from

DNA » RNA » protein

DNA

Deoxyribonucleic acid. Made of deoxyribonucleotides

• double-helix and double-stranded with complementary nitrogenous bases

  • Adenine «» Thymine

    • paired by 2 hydrogen bonds

  • Cytosine «» Guanine

    • paired by 3 hydrogen bonds ; stronger bond

• melting/denaturing separates strands

• antiparallel: runs/grows in opposite directions

  • one strand runs from 3’C to 5’C

  • another runs opposite from 5’ to 3’

  • note: ‘ or “prime” refers to attachments to [__]’s 5-carbon sugar/pentose backbone

RNA

Ribonucleic acid. Made of ribonucleotides

• shorter, single-stranded molecule

  • Adenine «» Uracil

  • Cytosine « » Guanine

Three types of [__]:

mRNA: messenger [__] » translated and used to make a protein

rRNA: ribosomal [__] » structural [__] that makes up the ribosome

tRNA: transfer [__] » responsible for bringing amino acids to ribosome to be added to the peptide chain/growing protein

Transcription

Process of taking information from certain genes in DNA and synthesizing a complementary mRNA (sends message to ribosomes on what proteins to produce)

3 steps

• Initiation: begins w/ binding of RNA polymerase to promoter; melts short portion of DNA to use as template strand

• Elongation:

• Termination:

RNA polymerase

Enzyme that carries out transcription

Makes RNA while DNA polymerase in DNA replication makes DNA ; does not need a RNA primer to attach to promoter

• promoter: nucleotide sequence to which [__] binds to start transcription

  • region “upstream” our gene

• terminator: a DNA sequence that tells [__] to stop the process of transcription

sigma factor

In bacteria, the RNA polymerase need this molecule to guide the RNA polymerase to the promoter to start initiation