topic 6 - final exam Flashcards
Describe how and why DNA is replicated
- To prepare for cellular division dna replication occurs (in the S phase of cell cycle)
- Is semiconservative replication
4 main steps
INITIATION
Helicase enzyme unwinding the double heliex - Strands separated by spinning at 10 000 rmp
- Hydrogen bonds broken
- Molecule unwinds
- Forms replication fork
- Each strand then acts as a template for the DNA replication process
PRIMER BINDING
- DNA replication initiaded by the binding of short RNA prmer to ssDNA
- Nucleotides can only be added to the 3’ end of an existin nucleotide chain
- RNA primer synthesized by the enzyme, primase
ELONGATION
- Adding DNA nucleotide to the primer
- By DNA polymerase III synthesizing in 5’ to 3’ direction uses 3’ to 5; direction template DNA
- Discontinuous DNA relication: DNA synthesis in short fragments (Okazaki fragments) on the lagging stramd
- 4 types of nucleotides
Deoxyribosnucleoside triphosphates (dNTPs: dATP, dGTP, dCTP, dTTP)
- Base pairing error may occur in DNA rplication
Need for proofreading
- DNA polymerase is able to proofread and correct errors
Removing incorrect nucleotides
TERMINATION
- DNA polymerase I removes RNA with DNA
-
- DNA ligase connects fragment to form on continuous strand
Define what constitutes a gene structure
gene refers to the oranisation of specific sequence elements within a gene. genes are segemnts of DNA that contain the code for a polypeptide chains aa sequence, as well as regulatory sequences that control gene expression.
Describe how gene expression is controlled through the actions of regulatory proteins, using lac operon as an example
Negative regulation via lac repressor
- Absence of lactose: repressor bound to operator (negative regulation)
- Lactose absent, repressor bound to operator, operon repressed.
Presence of lactose: allolactose binds to repressorcausing it t become an inactive form
- Lactose present, repressor not bound to operator operon derepressed.
-
Positive regulation via catabolite activator protein (CAP)
- CAP also known as cAMP Receptor protein (CRP)
- CAP-cAMP complex facilitates RNA polymerase binding to promoter (positive regulation)
- Light house
Outline how gene expression is controlled in eukaryotes
eukaryotic gene regulation
- occurs at 5 different levels
1. genomic eg., chromatin decondensation (euchromatin) and condensation (heterochromatin)
- euchromatin are dna undergoing transcription
2. transcriptional eg presence of enhancers or silencers
3. post-trancriptional (RNA processing and nucleo export)
- RNA splicing to remove introns forming mature mRNA
4. Transitional – binding of a translational repressor
5. Post- translational eg phosphorylation/dephosporylation
Define and describe DNA mutation
Dna mutation is any alteration in dna
Source of new gene
Source of gene diversity
May result in abnormal protein produced (if mutation is in the gene coding region)
Causes small to large scale changes
compare and contrast between spontaneous and induced mutations
Non induced (spontaneous) mutations
Unknown that may occur anytime, anywhere
Damaged genes (resulted from DNA replication without repair)
More common in organisms with short generation times (eg viruses and bacteria)
Induced mutations
- Exposure to mutagens
o Natural (uv lights, cosmic rays, radon)
o Induced
Chemical (nitrosguanidine, colchicine
Physical (gamma rays, x-rays)
Biological (virus)
Man made (asbestose and nuclear fallout)
compare and contrast the difference in somatic vs germinal mutations
Somatic mutations are not passed onto offspring where as germanal mutations can be
identify small scale mutations at the DNA level
small scale mutations (dna level)
- INDEL (insertion or deletion)
- Base substitution (transition or transversion)
purine to pyrimidines vice versa = transversion mutation
purine to purine
pyrimidine to pyrimidine
= transition
purine (A, G)
have 2 circles (wedding rings)
pyrimidne ( C, T, U)
have one circle
describe large scale mutations
Large scale mutation
Chromosome mutation abnormalities in chromosome number
can lead to a deletion, of a chromotid, duplication, translocation, inversion
state the different types of mutations in proteins
Affects PROTEIN synthesis in many ways
- Frameshift
o Due to insertion or deletion of DNA base
o Addition of T(in example) changed the reading frame
o May result in devastating effect since entire sequence may be changed
- Missense
o Due to substitution of DNA (T -> A)
o Resulted in change in mRNA sequence and therefore, a change in AA
o
- Nonsense
o Due to substitution of DNA base (T -> A)
o Resulted in STOP codon added
- Silent
o Due to substitution of DNA base (C -> T)
o However, protein sequence is not changed
o Redundancy of the egenetic code reduced the change og point mutations altering the specified AA
Compare the two sequences of DNA below:
Sequence 1: AGC TTC AGT GAc TGA GCT GGC GTC GAC
Sequence 2: AGC TTC AGT GAt TGA GCT GGC GTC GAC
The two bases in lowercase are an example of:
transition
Compare the two sequences of DNA below:
Sequence 1: AGC TtC AGT GAT TGA GCT GGC TTC GAC
Sequence 2: AGC TaC AGT GAT TGA GCT GGC TTC GAC
The two bases in lowercase are an example of:
transversion
The normal sequence of genes along a hypothetical chromosome is ABCDEFGH, where letters represent genes and the asterisk () represents the centromere. A mutation event occurs, resulting in a chromosome with the following sequence of genes: ABC*DFEGH. This mutation is an example of:
inversion
define a regulatory gene
encodes protein that regulates gene expression
define structural gene
encodes protein/rRNA/tRNA that is not a regulatory gene
