L1: Genetic Principles of Medicine: Nucleic Acids, Genes, and Chromosomes Flashcards
1
Q
genome
A
- the sum of genetic information for an organism
2
Q
gene
A
- a specific sequence of DNA that encodes a specific protein
3
Q
How much DNA in the human genome codes for proteins?
A
- low
- only around 1.2%
4
Q
What is non-coding DNA used for
A
- needed to control expression of genes
5
Q
Rank size of chromosome, gene, genome, and nucleotide
A
- nucleotide < gene < chromosome < genome
6
Q
chromosome
A
- a single molecule of genomic DNA
7
Q
genome of prokaryotes
A
- small, simple genomes
- circular or linear DNA molecules
8
Q
genome of eukaryotes
A
- large genomes
- lots of extra DNA
- long, linear DNA molecules
9
Q
origin of replication in prokaryotes
A
- single site of origin
10
Q
origin of replication in eukaryotes
A
- large genome and multiple sites of origins of replication
11
Q
What challenges do eukaryotes face due to their large genomes and linear chromosomes?
A
- because the genome is large, that makes it difficult to replicate
12
Q
what happens as DNA strands are separated on one side of the fork?
A
- DNA on the other side becomes supercoiled
13
Q
role of type I topoisomerase
A
- nicks one DNA strand to allow relaxation of supercoiling
- then seals the nick
14
Q
role of type II topoisomerase
A
- makes double-stranded break in one duplex of DNA
- unbroken duplex is passed through ends of break
- break is sealed and enzyme releases DNA
15
Q
template
A
- basis for instruction
16
Q
origins of replication
A
- defined sites where replication begins
17
Q
helicase
A
- unwinds DNA at fork
- present template for instruction
- breaks the Watson-Crick base pairs that form double helix
18
Q
topoisomerases
A
- resolve knots and supercoils
- deals with increased helical tension in advance of the fork
19
Q
SSB proteins
A
- stabilize unwound DNA that is now single-stranded
20
Q
RNA primers
A
- initiate DNA synthesis
21
Q
DNA polymerases
A
- make new DNA
22
Q
ligase
A
- resolves Okazaki fragments
23
Q
mismatch repair process
A
- certain DNA polymerases have exonuclease activity that can correct the mistakes
- cells are provided with the mismatch repair process when polymerase exonuclease activity fails
- mismatch repair process recognizes errors then correct those errors in the newly synthesized strand
- MSH2, MSH3, and MSH6 tasked with this
24
Q
Lynch syndrome
A
- caused by mutations in the mismatch proteins
- limit the efficiency of the DNA repair process
- lead to inherited form of colorectal cancer (HNPCC)
25
role of centromeres
- guide accurate segregation during cell division
| - spindle fibers attach and guide the chromosomes
26
role of telomeres
- protect ends of chromosome and guard against erosion from the ends
27
what is a telomere?
- short, repeated sequences found at the end of each chromosome
28
telomere as a buffer
- chromosomes have some sequence that acts as a buffer
| - can be lost without losing any protein-coding genes
29
in which cells are the gene that encodes for telomerase present?
- all cells
30
when is the gene that encodes for telomerase expressed?
- in different cancers usually
- in stem cells
- NOT in neurons - those are post-differentiated
31
how does packaging of DNA work?
- DNA wrapped around histone octomer to form nucleosome
- further condensed until we get "beads on a string"
- packaged further
- regulated by post-translational modification of histones
32
what happens when DNA is highly condensed?
- it is not possible for transcriptional machinery to reach DNA
33
open DNA
- euchromatin
34
closed DNA
- heterochromatin
35
Eukaryotic nuclear DNA is organized into ________ chromosomes.
Linear
36
What ensures fast DNA replication in eukaryotic cells?
Multiple origins of replication.
37
Describe how DNA is replicated in Prokaryotes.
1. Local opening of the double helix at a single origin of replication
2. Formation of a replication bubble flanked by replication fork at each end.
3. DNA replication occurs in a bidirectional manner
4. 2 circular DNA molecules result, each containing one parental and one daughter strand.
38
During DNA replication, the _______ strand requires repetitive action of ligase to join DNA fragments.
Lagging
39
Caused by mutations in key DNA-repair factors and leads to a familial form of colorectal cancer.
Lynch syndrome.
40
Name 2 useful repetitive sequences in DNA.
Centromeres and Telomeres.
41
Function of telomerase.
Enzyme that adds repetitive sequences to the ends of chromosomes.
42
What is a nucleosome?
The basic unit of chromosome structure - contain DNA wrapped around a histone octamer.
43
How are nucleosomes packaged?
Nucleosomes are futher packaged on top of each other and folded into a series of loops, which are further condensed to produce the mitotic chromosome.
