microbio chapter 8 (1 of 3) (exam3 )

·       Explain the central dogma of molecular biology

refers to the flow of genetic information

information is stored within DNA —> through transcription is converted into RNA —> goes through translation to produce proteins

Can’t backtrack!!!!

Define and explain the relationships between the following terms:

o   Genetics

o   Genes

o   Genome

Chromosomes

Genetics: study of heredity including how DNA stores information, how information stored within DNA is accessed, how it’s replicated

Genes: segments of DNA that encode functional proteins

Genome: all the genetic information in a cell (including chromosomes and other forms of DNA like plasmids)

Chromosomes: large pieces of DNA that store essential genetic info

·       Describe the molecular structure of DNA

DNA forms a double helix

• backbone consist of deoxyribose-phosphate

• two strands are held together by hydrogen bonds between complementary bases

  • A-T (2 H bonds)

  • C-G (3 H bonds)

• Strands are antiparallel

  • 5’ and 3’ ends

• order of bases forms genetic instructions of organism

Explain why the complementary nature of DNA is essential for its replication

One strand acts as a template for the production of a new strand

• enzymes read the original code and pair nucleotides up to match with their specific partners.

• Ensures that both double helixes are exact clones of the original molecule.

• high precision

Explain why DNA replication is semi-conservative

each new DNA molecule consists of one original strand from the parent and one completely brand new strand

describe the role of Helicase enzyme in DNA replication

separates the DNA strands- unzips DNA

• breaks the hydrogen bonds between base pairs (denatures DNA)

• revelas the bases so the strand can be used as a template for the snythesis of a new strand

• Forms a replication fork

  • one fork moves in clockwise direction, other fork is counter-clockwise

• As helicase unzips the DNA, stabilizing proteins bind the single stranded DNA

describe the role of primase enzyme in DNA replication

once helicase has unzipped DNA to reveal the bases, RNA primase synthesizes a short RNA primer that is complementary to the sequence of the template strand

• the RNA primer is single-stranded (and will eventually get replaced)

• the RNA primer is needed because DNA polymerase can’t initiate DNA synthesis on its own

describe the role of DNA polymerase enzyme in DNA replication

once an RNA primer has been synthesized, DNA polymerase adds nucleotides to the growing DNA strand

• Reads the template the 3’ to 5’ direction and synthesizes DNA in the 5’ to 3’ direction

describe the role of RNase enzyme in DNA replication

After DNA polymerase begins synthesizing DNA, the RNA primer is removed by RNase

on one strand, DNA is synthesized continuously —> leading strand

• DNA polymerase moving towards helicase

on other strand, DNA is synthesized in short patches —> lagging strand

• DNA polymerase is moving away from the helicase

• Short patches sealed together

describe the role of ligase enzyme in DNA replication

The short patches (okazaki fragments) are sealed together by ligase “glue”

·       Explain the occurrence of leading and lagging strands

Describe how replication forks move around a circular bacterial chromosome

  Explain how the cell accesses information stored within DNA

Transcription! (what genes should be expressed at what level)

• RNA polymerase locates the specific section of DNA that holds the instructions

• Unzips the double helix to expose genetic code inside

• Reads exposed DNA letters and creates a temporary matching copy called mRNA

Identify the difference between DNA nucleotides and RNA nucleotides

RNA uses a sugar called ribose which has a 2’ OH group instead of deoxyribose. This change makes RNA single stranded rather than a double helix, letting it easily move around the cell

Explain the role of the promoter in transcription

RNA polymerase binds to DNA at a promoter which is a DNA sequence that directs RNA polymerase to the start of a gene

happens in initiation (stage 1/3 of transcription)

·       Distinguish between DNA polymerase and RNA polymerase

Explain what is meant by ‘expression level’

Many RNAs are produced from a single gene

Highly expressed = many RNA molecules are produced

·       Explain how the genetic code is used to access information from DNA

Accessing information stored within DNA and converting to mRNA will be used as instruction for protein production

·       Distinguish between sense codons and nonsense codons

Sense codons: 61 of them for 20 amino acids

• amino acids are encoded by multiple codons —> degenerate/redundant

3 nonsense (stop) codons that terminate translation

1 start codon (AUG)

·       Describe the structure of ribosomes

made up of a large subunit and small subunit

·       Explain the role of tRNAs in translation

each tRNA carries a specific amino acid block, bottom loop contains a three-letter code called an anticodon, anticodon binds tightly to a matching triplet on mRNA, deposits the amino acid at the correct spot, empty tRNA leaves the ribosome to pick up more blocks

·       Describe the purpose of the A, P, and E sites within ribosomes

A: The A (aminoacyl) site is where new tRNA molecules carrying amino acids enter the ribosome; the

P (peptidyl) site holds the tRNA with the growing polypeptide chain, and the

E (exit) site is where empty tRNAs exit the ribosome after their amino acids have been added to the chain.

·       Explain how and why transcription and translation is coupled in bacteria

1. Transcription Begins: The enzyme RNA polymerase binds to bacterial DNA and starts making a single strand of messenger RNA (mRNA).

2. Ribosomes Attach Immediately: As the mRNA strand grows, its beginning (the 5' end) hangs out freely into the cell's cytoplasm.

3. Translation Starts: Ribosomes in the cytoplasm immediately grab onto this free end and start translating the genetic code into a protein chain, even while the RNA polymerase is still reading the DNA ahead of it.

Translation is performed by ribosomes

• mRNA is like a cook book, that contains the messages for protein synthesis (translation)

• Ribosomes see the codon (3 mRNA nucleotides that code for an amino acid

3 stages in transcription (RNA synthesis)

1. Initiation: RNA polymerase binds to DNA at a promoter (sequence that directs RNA polymerase to the start of a gene

2. Elongation: RNA polymerase adds RNA nucleotides to the 3’ end of the growing RNA strand

3. Termination: release of RNA polymerase and RNA fom the DNA