Unit 7 honors bio
Bacteriophage (phage): A virus that infects bacteria. Important in studies of genetic material transmission.
Base pairing rules (complementary pairing): The principle that adenine (A) pairs with thymine (T), and cytosine (C) pairs with guanine (G) in DNA.
DNA polymerase: Enzyme that adds complementary nucleotides to a growing DNA strand during replication. It also checks for mistakes and corrects them.
Double helix: The twisted ladder structure of DNA, formed by two complementary strands of nucleotides.
Helicase: An enzyme that unwinds the DNA double helix ahead of the replication fork.
Lagging strand: The DNA strand that is replicated in small segments (Okazaki fragments) in the direction opposite to the replication fork.
Leading strand: The DNA strand that is synthesized continuously in the direction of the replication fork.
Nucleotide: The monomer unit of DNA, consisting of a phosphate group, a sugar (deoxyribose), and a nitrogenous base (A, T, C, or G).
Okazaki fragments: Short DNA fragments formed on the lagging strand during DNA replication.
Purine: A type of nitrogenous base that has a two-ring structure. Examples: adenine (A) and guanine (G).
Pyrimidine: A type of nitrogenous base with a single ring. Examples: cytosine (C) and thymine (T).
Replication: The process by which DNA makes a copy of itself.
Replication origins (bubbles): Sites where DNA replication begins; the DNA is unwound into a bubble-like structure.
Semiconservative replication: A model of DNA replication where each new DNA molecule consists of one original strand and one newly synthesized strand.
Key People in DNA Research
Frederick Griffith: Discovered the process of bacterial transformation using Streptococcus pneumoniae.
Oswald Avery: Showed that DNA is the substance responsible for transformation, not proteins.
Martha Hershey and Alfred Chase: Conducted the famous experiment with bacteriophages to demonstrate that DNA, not protein, is the genetic material.
Rosalind Franklin & Maurice Wilkins: Used X-ray crystallography to capture images of DNA, leading to the understanding of its double helix structure.
James Watson & Francis Crick: Proposed the double-helix model of DNA, integrating Franklin’s X-ray data.
Erwin Chargaff: Discovered that the amount of adenine equals thymine, and the amount of cytosine equals guanine in a DNA molecule (Chargaff’s rules).
General DNA Composition and Structure
What two things does a chromosome consist of?
DNA
Proteins (mainly histones)
What did scientists believe was the molecule of inheritance before DNA was discovered? Most scientists believed proteins were the molecule of inheritance because of their complexity and diversity compared to DNA, which was thought to be too simple.
What is the monomer of DNA? A nucleotide, consisting of:
A phosphate group
A deoxyribose sugar
A nitrogenous base (A, T, C, or G)
What part of the nucleotide varies between the 4 nucleotides? The nitrogenous base is what varies.
Bonding in DNA:
Phosphate and sugar bonds (phosphodiester bonds): These form the backbone of the DNA strand, and they are strong bonds.
Base pairing (hydrogen bonds): These form between the complementary nitrogen bases (A-T, C-G) and are weak bonds, which is important for DNA to be easily unwound and replicated.
Purines vs Pyrimidines:
Purines: Adenine (A) and Guanine (G), have two rings in their structure.
Pyrimidines: Cytosine (C) and Thymine (T), have one ring in their structure.
Base Pairing: A pairs with T (2 hydrogen bonds) and C pairs with G (3 hydrogen bonds).
DNA Replication
When does DNA replication occur? During S-phase of the cell cycle (Synthesis phase of Interphase).
Where does DNA replication occur in eukaryotic cells? In the nucleus.
Why does DNA replication occur? So that each daughter cell receives an exact copy of the genetic material.
Key players in DNA replication:
Helicase: Unwinds the DNA double helix.
Single-strand binding proteins (SSBs): Keep the single-stranded DNA stable and prevent it from re-annealing.
DNA polymerase: Adds complementary nucleotides to the growing DNA strand. It also has proofreading capabilities.
Primase: Adds a short RNA primer so DNA polymerase can begin replication.
Ligase: Joins Okazaki fragments on the lagging strand.
Leading strand: Synthesized continuously in the direction of the replication fork.
Lagging strand: Synthesized in fragments (Okazaki fragments) because it’s replicated in the opposite direction to the replication fork.
Why is replication semi-conservative? Because each of the two new DNA molecules consists of one old strand and one new strand.
Primary functions of DNA:Stores genetic information.
Directs the synthesis of proteins.
Complementary bases in DNA:
A pairs with T.
C pairs with G.
Monomer of RNA: A nucleotide, which is similar to DNA but contains ribose instead of deoxyribose, and has uracil (U) instead of thymine (T).
Differences between DNA and RNA:
Sugar: DNA has deoxyribose; RNA has ribose.
Base: DNA has thymine (T), RNA has uracil (U).
Strands: DNA is double-stranded; RNA is single-stranded.
Protein Synthesis Process
Transcription: The process of copying the DNA code onto mRNA. It occurs in the nucleus.
Translation: The process of using mRNA to build a protein at the ribosome in the cytoplasm.
Codon: A set of 3 mRNA nucleotides that codes for a specific amino acid.
tRNA: Transfers amino acids to the ribosome based on the mRNA codon sequence.
rRNA: Makes up the structure of the ribosome.
Splicing: The process of removing introns and joining exons in pre-mRNA to form mature mRNA. It occurs in the nucleus. Introns are removed, exons stay in the nucleus and are expressed.
Translation:
mRNA carries the genetic code from DNA to the ribosome.
tRNA matches its anticodon with mRNA codons, bringing the correct amino acid.
The ribosome forms peptide bonds between amino acids to create the protein.
Mutations
Point mutations (substitutions, insertions, deletions) can change the sequence of amino acids in a protein, potentially altering its function.
Silent mutation: No effect on the protein.
Missense mutation: A single amino acid is changed.
Nonsense mutation: The change creates a stop codon, shortening the protein.
Frameshift mutation: Insertion or deletion of nucleotides shifts the reading frame, potentially altering every subsequent amino acid.
Example Sequence to Complete
Given the DNA coding strand:
TAC TCC CCG GAG AAT GTC CTA TCC GGC ATC
mRNA codons:
AUG AGG GGC CUC UUA CAG GAU AGG CCG UAG
Amino acids:
Methionine (Met) - Arginine (Arg) - Glycine (Gly) - Leucine (Leu) - Glutamine (Gln) - Aspartate (Asp) - Arginine (Arg) - Proline (Pro) - Stop
Sure! Here’s an overview of the specific jobs and processes that lead to the formation of DNA and RNA:
DNA (Deoxyribonucleic Acid)
Job/Function:
Storage of Genetic Information: DNA serves as the blueprint for all living organisms. It contains the instructions needed for the development, functioning, growth, and reproduction of all cells.
Cell Division: DNA ensures that genetic information is passed accurately during cell division, ensuring that offspring cells inherit the correct genetic material.
Formation/Process:
DNA Replication: The process by which DNA makes an identical copy of itself before cell division. This occurs during the S phase of the cell cycle.
Steps:
Unwinding: The double helix of DNA unwinds with the help of enzymes like helicase.
Base Pairing: DNA polymerase adds complementary nucleotides to each original strand (template strand) to form new strands.
Proofreading: DNA polymerase also checks for errors and corrects them to ensure accuracy.
End result: Two identical DNA molecules are produced, each consisting of one old strand and one new strand (semiconservative replication).
RNA (Ribonucleic Acid)
Job/Function:
Protein Synthesis: RNA plays a crucial role in converting genetic information from DNA into proteins, which are essential for various cellular functions.
Messenger RNA (mRNA) carries the genetic code from DNA to the ribosome for protein synthesis.
Transfer RNA (tRNA) helps in translating the mRNA code into a sequence of amino acids to form proteins.
Ribosomal RNA (rRNA) forms the structure of ribosomes and aids in protein synthesis.
Formation/Process:
Transcription: This is the process by which an RNA molecule is synthesized from a DNA template.
Steps:
Initiation: RNA polymerase binds to a specific region of the DNA (the promoter) to start transcription.
Elongation: RNA polymerase moves along the DNA template strand and synthesizes the RNA strand, adding RNA nucleotides that are complementary to the DNA sequence.
Termination: The RNA polymerase reaches a termination signal, and the RNA molecule is released.
End result: The RNA transcript (mRNA) is formed and can then be processed and used in translation.
Comparison in the Context of Protein Synthesis:
DNA contains the genetic information that codes for proteins but cannot directly participate in protein synthesis. It stays in the nucleus of eukaryotic cells to protect the genetic code.
RNA acts as the intermediary between DNA and proteins:
mRNA is transcribed from DNA and carries the code for protein synthesis to the ribosome.
tRNA helps translate this code into a specific sequence of amino acids, forming proteins.
rRNA is a structural component of the ribosome, facilitating the assembly of amino acids into proteins.