7-10 Flashcards
(61 cards)
1
Q
Why is it called “semi-conservative”?
A
- Conservative: Original strand is kept intact
- Semi-conservative: Each new DNA molecule conserves one strand from the original DNA and synthesizes a new strand
2
Q
DNA Helicase
A
- Unwinds the two strands at replication fork by destroying hydrogen bonds
3
Q
Single-Strand Binding Proteins
A
- Bind to unpaired DNA strand to prevent them from binding again
4
Q
Topoisomerase
A
- Relieves tension and prevents supercoiling
5
Q
RNA Primase
A
- Adds RNA primer to start replication
6
Q
DNA Polymerase 3
A
- Adds nucleotides by reading template strand which is 3’ to 5’ and creating a strand that is 5’ to 3’
7
Q
DNA Polymerase 1
A
- Removes RNA primers and fills in the gaps between DNA fragments
8
Q
Rate of Elongation
A
- 500 nucleotides per second in bacteria
- 50 nucleotides per second in human cells
9
Q
Requirements of DNA Polymerase
A
- Must have 3’OH group to add on to
10
Q
Lagging Strand
A
- Multiple RNA primers
- DNA polymerase and RNA primase is constantly going back and forth to replicate DNA
- DNA Ligase glues all the Okazaki fragments together
11
Q
Ends of DNA Replication Problem
A
- We can’t place RNA primer on the very end
- So DNA becomes shorter and shorter every generation
- To prevent this telomeres extends the length of the chromosome and the DNA polymerase can finish replicating the rest of the lagging strand
12
Q
Why do Cells Divide?
A
- Growth
- Repair/Regeneration
- Reproduction
13
Q
Binary Fission
A
- Asexual reproduction in bacteria
- The origin of replication is attached to opposite sides of plasma membrane
- Cell elongates and plasma membrane pinches inwards
14
Q
Gene vs. Chromosome
A
- A gene is a segment of DNA that carries the instructions for making a specific protein or RNA molecule
- A chromosome is a long, coiled structure made of DNA and proteins. It contains many genes
15
Q
DNA Packaging
A
- DNA wraps around histones which forms a nucleosome
- Many nucleosomes coil and stack together to form chromatin which condenses DNA
- Chromatin loops and folds to form chromosomes which condenses DNA even more
16
Q
Interphase 1
A
- Chromatin wrap around histone proteins
- G1: Cellular contents are duplicating and grows in size
- S: Chromosomes are replicated
- G2: DNA Polymerase proofreads
17
Q
Mitotic Phase
A
- Division of nucleus and duplication of cytoplasm
18
Q
Mitosis: Interphase
A
- G2
19
Q
Mitosis: Prophase
A
- DNA becomes packaged and the two centrosomes begin to move to opposite end of cells
20
Q
Mitosis: Prometaphase
A
- Nuclear envelope breaks down
21
Q
Mitosis: Metaphase
A
- Chromosomes align at the cell’s center
22
Q
Mitosis: Anaphase
A
- Sister chromatids separate and move toward opposite poles
23
Q
Mitosis: Telophase
A
- New nuclear membranes form around the separated chromosomes
24
Q
Mitosis: Cytokinesis
A
- The cytoplasm divides, forming two separate cells
25
Cytokinesis in Plant Cell
- Cell plates are formed in mid cell at end of telophase
- No cleavage furrow is formed like in animal cells
26
Apoptosis
- Programmed cell death
- Removes unwanted cells during development
- Removes damaged cells throughout life
27
Meiosis: Prophase 1
- Genetic material is condensed into chromosomes
- Spindle fibres form around cell
- Synapsis occurs, homologous pairing of chromosomes
- Crossing over may occur, exchange of alleles
28
Meiosis: Metaphase 1
- Tetrads (pairs of homologous chromosomes) move to centre and line up in homologous pairs
- Spindle fibres attach to centromeres of each chromosome
29
Meiosis: Anaphase 1
- Sister chromatids separate together moving to opposite poles of cell
30
Meiosis: Telophase 1
- Chromosomes decondense and nuclear envelope reforms
31
Meiosis: Cytokinesis
- Cell divides into two daughter cells
- DNA is chromatin
32
Differences in Meiosis 2
- SYNAPSIS DOES NOT OCCUR
- CROSSING OVER DOES NOT OCCUR
- CHROMOSOMES ALIGN IN SINGLE FILE
33
Stage 1 Initiation:
1. DNA is unwound by RNA polymerase
2. Promoter signals RNA polymerase where and when to start transcription
34
Stage 2: Elongation
- RNA polymerase moves down the DNA strand from 3’ to 5’ while creating a mRNA strand
35
Stage 3: Termination
- Terminator signals RNA polymerase where and when to end
- mRNA polymerase falls of DNA strand
36
Transcription in Prokaryotic
- Transcription and translation occur simultaneously in the cytoplasm.
- mRNA is directly translated into proteins without the need for further processing
37
Initiation in Eukaryotes
- Within the promoter there is the TATA box
- T and A have only two hydrogen bonds so it’s easier for RNA polymerase to pull apart
- Transcription factors are proteins that bind to promoter that know which gene needs to be transcribed
- This stop RNA polymerase for transcribing liver genes in brain for example
38
mRNA processing
- Before the mRNA is exported from the nucleus 5' cap is added to protect the mRNA from degradation and aid in ribosome binding
- Poly(A) tail is added to the 3' end for stability and transport
39
mRNA Processing: Splicing
- Exons are going to be expressed
- Introns are not going to be expressed so they are spliced out
- Exons can be spliced out in different ways to produce different proteins from the same gene
40
Genetic Code
- Three nucleotides code (codon) for each amino acid
- 64 possible codons
- The genetic code is universal, meaning that almost all living organisms use the same codons
41
tRNA
- Transfer amino acids from cytoplasm to ribosome
- Contains anticodon that is paired with codon on mRNA
- Contains cloverleaf structure which allows it to fold into 3D structure
- Contains complementary amino acid for codon
42
Aminoacyl-tRNA Synthesia
- Ensures a specific amino acid is joined to specific tRNA
1. Aminoacyl-tRNA Synthesia contains specific binding site that recognises specific amino acid
2. ATP is broken down
3. Amino acid is now linked to an AMP, forming an aminoacyl-AMP complex
4. Activated aminoacyl-AMP complex then binds with the tRNA
5. Amino acid is transferred from the AMP group to the tRNA, forming an
43
Ribosome
- A site is where tRNAs carrying amino acids bind
- P site is where the growing polypeptide chain is held
44
Translation: Initiation:
- Read from 5’ to 3’
- Start codon begins ribosome reading
- Very first amino acid is codon “AUG” which is amino acid “Met”
- Large ribosomal unit is then placed on top of mRNA strand like this. GTP (ribosomal version of ATP) is the energy used for this placement
45
Translation: Elongation
- The amino acid from the tRNA in the A site is added to the growing polypeptide chain in the P site
- 2GTP is used to collect tRNA and attach amino acid
- Translocation: The ribosome moves to the next codon on the mRNA, shifting the tRNAs from the A site to the P site
46
Translation: Termination
- Release factor protein binds to the ribosome at A site
- This causes the ribosome to dissociate, and the newly synthesised protein is released from the tRNA
47
Control of Gene Expression in Prokaryotes
- Operons (groups of genes) are often controlled together, with a single promoter initiating transcription for multiple genes
- Bacteria can simultaneously transcribe and translate mRNA
48
Control of Gene Expression in Eukaryotes
- Transcriptional control: Involves transcription factors that help or inhibit RNA polymerase from transcribing a gene
- Post-transcriptional control: Includes mRNA splicing, capping, and the addition of a poly(A) tail to help stabilize the mRNA.
- Post-translational control: Proteins can be modified, transported, or degraded after translation
49
Mutation
- Change in nucleotide sequence of DNA
50
Mutagen
- Chemical, biological or physical agent that interacts with DNA and causes mutation
- E.G. Tobacco, X-rays, Certain viruses
51
Point Mutation
- Changes to a single base of DNA or RNA
1. Substitution - One base is replaced by another
2. Insertion - A new base is inserted
3. Deletion - A base is deleted
4. Inversion - A segment of sequence is flipped (ATG → AGT)
52
Small-Scale Mutation in Genes
1. Silent Mutation - changes in DNA that does not cause change in amino acid
2. Missense Mutation - Changes in DNA that changes one amino acid
3. Nonsense Mutation - Changes in DNA that shortens polypeptide and results in non-functional protein
4. Frameshift Mutation - One base being either inserted or deleted, altering every codon in that sequences from that point onwards
53
Chromosomal Mutations
- Larger segments of DNA or entire chromosomes
1. Deletion - Removal of segment of chromosome
2. Duplication - Replication of segment of chromosome
3. Translocation - Segment of chromosome is moved to another chromosome
4. Inversion - Segment of chromosome is rotated 180 degrees
54
Aneuploidy
- Abnormal number of chromosomes (e.g. Down syndrome with an extra chromosome 21)
55
Polyploidy
- Having multiple sets of chromosomes
56
Induced Mutations
- Caused by external
- Physical, chemical and biological
57
Spontaneous Mutations
- Arise naturally without external influence
- DNA replication errors by DNA polymerase
- Chemical changes in nucleotides, such as deamination.
- Unrepaired DNA damage caused by reactive metabolites in the cell
58
DNA Damage Repair
1. Pyrimidine Dimer Formation
- UV light causes adjacent thymine or cytosine bases to covalently bond
2. Nucleotide excision repair (NER)
- Damage recognition: Proteins bind to the damaged DNA region
- Incision: Enzymes cut out the damaged section
- Gap filling: DNA polymerase synthesizes new DNA to replace the gap
- Ligation: DNA ligase seals the strand
59
Xeroderma Pigmentosum (XP)
- A genetic disorder caused by defects in the NER pathway, making individuals highly sensitive to UV light
60
Beneficial Mutations
- HIV resistance: A mutation in the CCR5 gene makes individuals resistant to HIV infection
- Sickle cell anemia: A mutation that provides resistance to malaria in certain populations
61
Harmful Mutations
- Phenylketonuria (PKU): A mutation that causes the inability to metabolise phenylalanine, leading to brain damage if untreated.
- Cystic fibrosis: A mutation in the CFTR gene that causes thick mucus buildup in the lungs and digestive system
