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Lecture 2 - Genes Flashcards

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0
Q

Repetitive Sequence DNA

A

Regions of non-coding DNA found only in euk.

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1
Q

Gene

A
  • Series of DNA nucleotides that generally codes for the production of a single polypeptide or mRNA, rRNA, or tRNA
  • Referred to as a unique sequence DNA - unique sequence DNA dominates
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2
Q

Eukaryotes and Genes

A

Have more than one copy of some genes

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3
Q

Prokaryotes and Genes

A

Have only one copy of each gene

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4
Q

Euchromatin

A

Regions of DNA associated with eukaryotic genes that are being actively transcribed by a cell

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5
Q

Heterochromatin

A
  • Tightly packed regions of DNA associated with genes not being actively transcribed
  • Repetitive sequence DNA is found mainly in heterochromatin
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6
Q

ONE GENE = ONE POLYPEPTIDE … What’s the exception?

A

Posttranscriptional processing RNA

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7
Q

Genome

A
  • Entire DNA sequence of an organism
  • Btwn 26,000 to 38,000 genes in the human genome
  • Only a little over 1% of a human genome actually codes for protein
  • Variation of nucleotide sequence among humans is small, 0.08%
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8
Q

The Central Dogma of Gene Expression

A
  • DNA is transcribed to RNA, which is translated to amino acids forming a protein
  • DNA –> RNA –> Protein
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9
Q

DNA

A
  • Deoxyribonucleic acid
  • polymer of nucleotides
  • DNA nucleotides differ only in their nitrogenous bases
  • The end 3’ C is attached to an -OH group
  • The end 5’ C is attached to a phosphate group
  • Double stranded structure, antiparallel, bound by H bonds btwn nitrogenous bases
  • 2 strands that match w/ correct b.p. are complementary strands and curl into a double helix
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10
Q

What are the nitrogenous bases that exist in DNA?

A

Adenine, guanine, cytosine, and thymine

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11
Q

How are the nucleotides bound in DNA?

A

Phosphodiester bond between the 3rd C of one deoxyribose and the 5th C of the other creating the sugar-phosphate backbone of a single strand of DNA w/ 5’ to 3’ directionality

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12
Q

Base-pairing is referred to as…?

A

Hydrogen bonding

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13
Q

How is the length of DNA measured?

A

In base-pairs

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14
Q

Double Helix

A
  • Contain major and minor groove
  • Each groove spirals once around double helix for every 10 b.p
  • Diameter is ~ 2 nm or 13x the diameter of a C atom
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15
Q

Purines

A
  • nucleotides
  • 2 ring structures
  • adenine and guanine
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16
Q

Pyrimidines

A
  • nucleotides
  • single ring structures
  • thymine and cytosine
  • uracil in RNA
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17
Q

Purine and Pyrimidine Pairs

A
  • A forms 2 H-bonds with T

- G forms 3 H-bonds with C

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18
Q

Replication

A
  • A cell replicates its DNA one time in each life cycle
  • DNA replication is semi-conservatie
  • Governed by a group of proteins called replisome
  • Begins toward the middle of chromosome at site called origin of replication
  • Bidirectional process
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19
Q

Semi-Conservative

A

When a new double strand is created, it contains one strand from the original DNA and one newly synthesized strand

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20
Q

Bidirectional Process

A

Proceeds in both directions from an origin, each direction produces a leading and lagging strand

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21
Q

Replication Fork

A

The point where a replisome is attached to the chromosome

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22
Q

Origins of Replication in Prokaryotes vs. Eukaryotes

A
  • A single eukaryotic chromosome contains multiple origins, while replication in prokaryotes takes place for a single origin on a circular chromosome
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23
Q

DNA Helicase

A

As part of the replisome, it unwinds the double helix separating the two strands

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24
Q

DNA Polymerase

A
  • Enzyme that builds the new DNA strand
  • Cannot initiate a strand from 2 nucleotides, but can only add nucleotides to an existing strand
  • Requires an RNA primer to get started
  • Adds deoxynucleotides to the primer and moves along each DNA strand creating a complimentary strand
  • Reading DNA is 3’ to 5’ , synthesizing DNA is 5’ to 3’
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25
Q

Primase

A
  • RNA polymerase

- creates an RNA primer approx. 10 ribonucleotides long to initiate the strand

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26
Q

Downstream

A

5’ to 3’

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27
Q

Upstream

A

3’ to 5’

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28
Q

Pyrophosphate Group

A
  • Two phosphates bounded together
  • Addition of each nucleotide to the new strand requires removal of a pyrophosphate group from a deoxynucleotide triphosphate
  • Some of the energy from the hydrolysis of the pyrophosphate is used to drive replication
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29
Q

Leading Strand

A

continuous new strand

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30
Q

Lagging Strand

A
  • Interrupted Strand, restarted with new primer

- Made from series of disconnected strands called Okazaki fragments

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31
Q

Okazaki Fragments

A

~ 100 to 200 nucleotides in eukaryotes and ~ 1000 to 2000 nucleotides in prokaryotes

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32
Q

DNA Ligase

A

Moves along lagging strand & ties okazaki fragments together to complete polymer

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33
Q

Semidiscontinuous

A

The process of replication is said to be since the formation of one strand is continuous and the other fragmented

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34
Q

Telomeres

A
  • Ends of eukaryotic chromosomal DNA possess them
  • Repeated 6 nucleotide units from 100 to 1,000 units long
  • Protect the chromosomes from being eroded through repeated rounds of replication
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35
Q

Steps of Replication

A
  1. Helicase unzips the double helix
  2. RNA polymerase builds a primer
  3. DNA polymerase assembles the leading & lagging strands
  4. The primers are removed
  5. Okazaki Fragments are joined
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36
Q

RNA

A
  • Ribonucleic acid
  • Can move through nuclear pores and isn’t confined to the nucleus, unlike DNA
  • Exists in 3 forms: mRNA, rRNA, tRNA
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37
Q

Structure of RNA

A

Identical to DNA in structure except:

  1. Carbon #2 on the pentose is not “deoxygenated”, it has a hydroxyl group attached
  2. single stranded
  3. RNA contains the pyrimidine uracil instead of thymine
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38
Q

mRNA

A
  • messenger RNA

- Delivers the DNA code for amino acids to the cytosol where the proteins are manufactured

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39
Q

rRNA

A
  • ribosomal RNA
  • combines with proteins to form ribosomes
  • synthesized in the nucleolus
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40
Q

Ribosomes

A

cellular complexes that direct the synthesis of proteins

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41
Q

tRNA

A
  • Transfer RNA

- Collects amino acids in the cytosol and transfers them to the ribosomes for incorporation into a protein

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42
Q

What does the similarity between uracil and thymine cause in DNA?

A

Common cause of mutations in DNA

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43
Q

Differences between DNA and RNA

A
  1. DNA made from deoxyribose; RNA made from ribose
  2. DNA is double stranded; RNA is single stranded
  3. DNA has thymine; RNA has uracil
  4. DNA is produced by replication; RNA is produced by transcription
  5. In animals, DNA is only in nucleus and mitochondria; RNA is also in the cytosol
  6. One major type of DNA; 3 major types of RNA
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44
Q

Transcription

A
  • All RNA is made from a DNA template in this process
  • It must take place in the nucleus or mitochondrial matrix b/c DNA can’t leave there
  • The steps are: Initiation, Elongation, and Termination
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45
Q

Initiation of Transcription

A
  • A group of proteins called initiation factors finds promotor on DNA strand, and assembles a Tx initiation complex, which includes RNA polymerase.
  • After binding to promoter, RNA poly unzips DNA double helix creating a Tx bubble.
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46
Q

RNA Polymerase

A
  • Prokaryotes have one type

- Eukaryotes have 3; one for each RNA.

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47
Q

Promoter

A
  • A sequence of DNA nucleotides that designates a beginning point for Tx.
  • In prokaryotes, its located at the beginning of the gene
  • The Tx start point is part of the promoter
  • The 1st b.p. located at the Tx start point is designated +1
  • B.p. located before the start point such as those in the promoter are designated by - #’s
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48
Q

Consensus Sequence

A
  • Most commonly found nucleotide sequence of a promotor recognized by the RNA poly of a given species
  • Variation from it causes RNA poly to bond less tightly and less often to a given promoter, which leads to those genes being transcribed less frequently
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49
Q

Elongation of Transcription

A
  • RNA poly transcribes only 1 strand of the DNA nucleotide sequence into a complementary RNA nucleotide sequence
  • Only 1 strand in a molecule of double stranded DNA is transcribed
  • This strand is called the template strand or antisense strand
  • The other strand, called the coding strand or sense strand, protects its partner against degradation.
  • RNA poly moves along the DNA strand 3’ to 5’, building the new strand 5’ to 3’
  • Tx proceeds 10x more slowly than DNA replication
  • RNA poly doesn’t have proofreading & rate of error of Tx is higher than replication
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50
Q

Termination of Transcription

A
  • End of Tx

- Requires special termination sequence and special proteins to dissociate RNA poly from DNA

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51
Q

Genetic Regulation

A
  • Replication makes no distinction between genes

- Genes are activated/deactivated at the level of Tx via proteins called activators and repressors

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52
Q

Why are genes activated/deactivated at the level of Tx?

A
  1. mRNA has a short half life in cytosol, after Tx is over, it’s degraded & protein is no longer translated
  2. Many proteins can be transcribed from a single mRNA, so there is an amplifying effect
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53
Q

Activators and Repressors

A
  • Bind to DNA close to the promoter, and either activate or repress the activity of RNA poly
  • Allosterically regulated by small molecules such as cAMP
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54
Q

Primary Function of Gene Regulation In Prokaryotes

A
  • To respond to the environmental changes

- Changes in gene activity are a response to the concentration of specific nutrients in & around the cell

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55
Q

Primary Function of Gene Regulation in Multicellular Organisms

A
  • Lack of change or homeostasis is the hallmark of multicellular organisms
  • To control the intracellular and extracellular environments of the body
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56
Q

Prokaryotic vs. Eukaryotic mRNA

A
  • Prok. mRNA includes several genes in a single transcript - polycistronic
  • Euk. mRNA includes only one gene per transcript - monocistronic
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57
Q

Operon

A
  • Sequence of bacterial DNA
  • The genetic unit, usually consisting of the operator, promoter, and genes that contribute to a single prokaryotic mRNA
  • Ex: lac operon
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58
Q

Lac Operon

A
  • Codes for enzymes that allow E. coli to import and metabolize lactose when glucose isn’t present in sufficient quantities
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59
Q

How does the lac operon work?

A
  • low glucose levels lead to high cAMP levels –> cAMP binds & activates CAP –> CAP binds to site adjacent to promoter on lac operon –> promoter is activated & allows Tx & Ts of 3 proteins –> operator serves as binding site for lac repressor –> lac repressor is inactivated by presence of lactose in cell –> lac repressor will bind to operator unless lactose binds to lac repressor
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60
Q

Location CAP site & Operator of Lac Operon

A
  • CAP site is located upstream to promoter

- Operator on lac operon is located downstream to promoter

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61
Q

Genes of Operon

A
  • Transcribed on one mRNA

- Genes outside operon may code for activators and repressors

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62
Q

Enhancers

A
  • Commonly used by eukaryotes b/c their gene regulation is more complicated, involving interaction of many genes
  • Their function is similar to activators/repressors, but they act at a much greater distance from the promoter
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63
Q

Post-Transcriptional Processing of RNA in Eukaryotes

A
  • Each type of RNA undergoes it

- Allows for additional gene regulation

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64
Q

Post-Transcriptional Processing in Prokaryotes

A
  • rRNA & tRNA go through it, but mRNA is directly translated to protein
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65
Q

Primary Transcript

A
  • The initial mRNA nucleotide sequence arrived at through transcription
  • AKA pre-mRNA or hnRNA
  • longer than mRNA that will be translated into a protein
  • Before leaving nucleus, it’s cleaved into introns and exons
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66
Q

How is the primary transcript processed?

A

3 ways:

  1. addition of nucleotides
  2. deletion of nucleotides
  3. modification of nitrogenous bases
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67
Q

5’ Cap

A
  • Even before eukaryotic mRNA is completely transcribed, its 5’ end is capped using GTP
  • 5’ cap serves as attachment site in protein synthesis & as protection against degradation by exonucleases
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68
Q

Polyadenylation of 3’ End

A

3’ end is polyadenylated with a poly A tail to protect it from exonucleases

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69
Q

snRNPs

A
  • Enzyme-RNA complexes
  • Recognize nucleotide sequences at the ends of the introns
  • Several associate with proteins to form a complex called a splicesome
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70
Q

Splicesome

A
  • Inside, the introns are looped bringing the exons together

- The exons are spliced together to form the single mRNA strand that ultimately codes for a polypeptide

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71
Q

Introns

A
  • Introns don’t code for proteins and are degraded within the nucleus
  • Intron sequences are much longer than exon sequences
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72
Q

Exons

A
  • Exons of some genes may be spliced in different order allowing them to code for different polypeptides
  • Average # of exons per gene is 7
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73
Q

Denaturation of DNA

A
  • Separation of the 2 strands of the double helix

- caused by heat, high [ ] salt solution, or high pH solution

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74
Q

Melting Temperature (Tm)

A
  • Temp needed to separate DNA strands
  • G & C base pairs have a greater Tm (b/c have 3 H-bonds)
  • Heating to 95 degrees celsius is generally enough to denature any DNA sequence (just below boiling point of water)
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75
Q

DNA vs. Denatured DNA

A
  • Denatured DNA is less viscous, denser, and more able to absorb UV light
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76
Q

Nucleic Acid Hybridization

A
  • When denatured, DNA prefers to be double stranded and will look for a complementary partner
  • Double stranded combinations can be formed through nucleic acid hybridization: DNA-DNA, DNA-RNA, & RNA-RNA
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77
Q

Hybridization Techniques

A

Allows scientists to identify nucleotide sequences by binding a known sequence with an unknown sequence

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78
Q

Restriction Enzymes

A
  • AKA restriction endonucleases
  • Digest or cut nucleic acid only at certain nucleotide sequence along the chain called a restriction site or recognition sequence.
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79
Q

How do bacteria use restriction enzymes?

A
  • Bacteria cut the viral DNA into fragments with restriction enzymes to defend themselves from viruses.
80
Q

How do bacteria protect their own DNA from restriction enzymes?

A
  • By methylation (adding -CH3)

- Methylation is usually associated with inactivated genes

81
Q

Palindromic Sequence

A
  • A restriction site is typically a palindromic sequence 4-6 nucleotides long
  • Reads the same backwards as forwards
82
Q

Sticky Ends

A
  • Most restriction enzymes cleave DNA strand unevenly, leaving complementary single stranded ends, these ends are called sticky ends
  • These ends can reconnect through hybridization
  • Once paired, the phosphodiester bonds of the fragments can be joined by DNA ligase
83
Q

Recombinant DNA

A
  • Two DNA fragments cleaved by the same endonucleases that can be joined together regardless of the origin of the DNA
  • Artificially recombined
84
Q

Recombinant DNA & Bacteria

A
  • Recombinant DNA can be made long enough for bacteria to replicate & then placed within the bacteria using a vector
  • The bacteria can then be grown in large quantities forming a clone of cells containing the vector with the recombinant DNA fragment
  • The clones can be saved separately forming a clone library
85
Q

Vector

A

A plasmid or an infective virus

86
Q

Clone Library

A
  • Not all bacteria take up the vector & not all vectors take up the DNA fragment
  • By including in the original vector a gene for resistance to a certain antibiotic and the lacZ gene (enables bacteria to metabolize the sugar X-gal), libraries can be screened.
87
Q

Screening Clone Libraries

A
  • When an antibiotic is added to a library, clones w/o resistance will be eliminated. (screens for clones that didn’t take up vector)
  • Clones w/ an active lacZ gene turn blue in the presence of X-gal, clones w/ the cleaved form of the gene don’t turn blue, clones w/ the DNA fragment will not turn blue when placed on medium w/ X-gal. (an endonuclease is also inserted to inactivate the lacZ gene)
88
Q

Probe

A

The radioactively labeled complementary sequence of the desired DNA fragment

89
Q

Complementary DNA

A
  • AKA cDNA
  • Eukaryotic DNA contains introns and bacteria have no mechanism for removing introns
  • Therefore its useful to clone DNA w/ no introns
  • In order to do this, the mRNA produced by the DNA is reversed transcribed using reverse transcriptase -> The DNA product is cDNA
  • Adding DNA polymerase to cDNA produces a double strand of the desired DNA fragment
90
Q

Polymerase Chain Reaction (PCR)

A
  • Fast way to clone DNA

- By heating to denature then cooling

91
Q

Southern Blotting

A
  • Technique used to identify target fragments of known DNA sequence in a large population of DNA
92
Q

Process of Southern Blotting

A
  • The DNA is cleaved into restriction fragments
  • Fragments are separated according to size by gel electrophoresis (larger move slower)
  • Gel is made alkaline to denature DNA
  • Membrane is used to blot gel which transfers the separated single stranded DNA fragments
  • A radio-labeled probe w/ a complementary nucleotide sequence is added to membrane
  • The probe hybridizes w/ & marks the target fragment, and then visualized w/ radiographic film
93
Q

Northern Blot

A
  • Same as southern blot but w/ RNA
94
Q

Western Blot

A

Detects a protein with antibodies

95
Q

Restriction Fragment Length Polymorphisms (RFLP)

A
  • Identifies individuals as opposed to specific genes

- The DNA fingerprints used to identify criminals in court cases

96
Q

Single Nucleotide Polymorphisms (SNPs)

A
  • Genome of one human differs from genome of another at about one nucleotide in every 1000
97
Q

Genetic Code

A

mRNA nucleotides are strung together to form a genetic code which translates the DNA nucleotide sequence into an A.A. sequence, and ultimately into a protein

98
Q

Degenerative

A

More than one codon can code for an A.A.

99
Q

Unambiguous

A

Any single series of 3 nucleotides will code for only 1 A.A.

100
Q

Codon

A

3 consecutive nucleotides on a strand of mRNA

101
Q

Stop Codons

A
  • don’t code for A.A.
  • UAA, UGA, & UAG
  • Signal an end to protein synthesis
102
Q

Start Codons

A
  • AUG

- Also acts as codon for methionine

103
Q

How are sequences of RNA nucleotides written?

A

5’ to 3’

104
Q

Figuring Out Probability of Possible A.A. Sequences

A 
Base = how many different ones there are
Exponent = how many there are
105
Q

Translation

A
  • Process of protein synthesis directed by mRNA

- Each of the 3 RNA’s play a role in Ts

106
Q

Role of mRNA

A

The template which carries the genetic code from the nucleus to the cytosol in the form of codons

107
Q

Role of tRNA

A
  • Contains a set of nucleotides that is complementary to the codon, called the anticodon
  • sequesters the A.A. that corresponds to its anticodon
108
Q

Role of rRNA

A
  • w/ protein makes up the ribosome, which provides the site for Ts to take place
  • Actively participates in Ts process
109
Q

Ribosome

A
  • composed of small & large subunit made from rRNA & many separate proteins
  • Prokaryotic ribosomes are smaller than eukaryotic ribosomes
110
Q

What are ribosomes and their subunits measured in?

A

Terms of sedimentation coefficients given in svedberg units (s)

111
Q

Eukaryotic Ribosome

A
  • 40s & 60s subunits, combined 80s

- manufactured in the nucleolus & exported separately to cytoplasm

112
Q

Prokaryotic Ribosome

A
  • 30s & 50s, combined 70s

- Don’t have nucleolus but synthesis is similar to eukaryotes

113
Q

Initiation of Translation

A
  • After posttranscriptional processing in a eukaryote, mRNA leaves the nucleus & enters cytosol
  • The 5’ end attaches to the small subunit w/ the help of initiation factors (proteins)
  • A tRNA possessing the 5’-CAU-3’ anticodon sequesters the A.A. methionine & settles in at the P site (peptidyl site)
  • This is the signal for the large subunit to join & form the initiation complex
114
Q

Elongation of Translation

A
  • A tRNA w/ its corresponding A.A. attaches to the A site (aminoacyl site) at the expense of 2 GTPs.
  • The C-terminus (carboxyl end) of methionine attaches to the N-terminus (amine end) of the A.A. @ the A site in a dehydration rxn catalyzed by peptidyl transferase
  • Then translocation occurs which requires 1 GTP
  • The tRNA that carried methionine moves to the E site where it can exit the ribosome
  • The tRNA carrying the newly formed dipeptide moves to the P site, clearing the A site for the next tRNA
  • Elongation repeats until stop codon reaches P site
115
Q

Translocation

A

The ribosome shifts 3 nucleotides along the mRNA toward the 3’ end

116
Q

Termination of Translation

A
  • When a stop (or nonsense) codon reaches the A site, proteins known as release factors bind to the A site, allowing a water molecule to add to the end of the polypeptide chain
  • The polypeptide is freed from the tRNA & ribosome, & the ribosome is broken up into its subunits to be used again for another round of protein synthesis
117
Q

Folding

A
  • As the polypeptide is being Ts, it begins folding
  • The A.A. sequence determines the folding conformation
  • The folding process is assisted by proteins called chaperones
118
Q

Post Translational Modification

A
  • Sugars, lipids, or phosphate groups may be added to an A.A.
  • Polypeptide may be cleaved in 1 or more places
  • Separate polypeptides may join to form quaternary structure of a protein
119
Q

Polypeptides Injected Into Lumen

A
  • Ts beings on a free floating ribosome
  • A signal peptide @ the beginning of the translated polypeptide may direct the ribosome to attach to the ER, in which case the polypep is injected into the lumen.
  • Polypeps injected into the lumen may be secreted from the cell via the golgi or may remain partially attached to the membrane
120
Q

Signal-Recognition Particle (SRP)

A

Carries entire ribosome complex to a receptor protein on the ER

121
Q

Mutation

A
  • Any alteration in genome that isn’t genetic recombination

- May occur @ chromosomal or nucleotide level

122
Q

Gene Mutation

A

Alteration in the sequence of DNA nucleotides in a single gene

123
Q

Chromosomal Mutation

A

When structure of chromosome is changed

124
Q

Somatic vs. Germ Cell Mutations

A

Mutations in somatic cells are not passed to offspring, mutations in germ cells are

125
Q

Spontaneous Mutation

A
  • Due to random errors in the natural process of replication & genetic recombination
  • Have same effect on cell as an induced mutation
126
Q

Induced Mutations

A
  • Due to physical or chemical agents called mutagens

- Have same effect on cell as spontaneous mutation

127
Q

Mutagen

A

Physical or chemical agent that increases the frequency of mutation above the frequency of spontaneous mutations

128
Q

Point Mutation

A

A mutation that changes a single base-pair of nucleotides in a double strand of DNA

129
Q

Example of a Point Mutation

A
  • Base-Pair substitution mutation: One b.p. is replaced by another
  • can be a transition mutation: A-T –> G-C
  • can be a transversion mutation: A-T –> T-A
130
Q

Missense Mutation

A
  • Base-pair mutation that occurs in the A.A. coding sequence of a protein, & an alteration of a single A.A. may or may not have effect on the function of a protein
  • Ex: Sickle Cell Anemia
131
Q

Frameshift Mutation

A
  • Insertion or deletion may result in this
  • Results when deletions or insertions occur in multiples of 3
  • Often result in a completely nonfunctional protein
132
Q

Nonsense Mutation

A
  • If a base-pair substitution or an insertion or deletion mutation creates a stop codon
  • Very serious -> stops Ts of a functional protein entirely
133
Q

Chromosomal Deletions

A

Portion of chromosome breaks off, or is lost during homologous recombination and/or crossing over events

134
Q

Duplications

A

When a DNA fragment breaks free of 1 chromosome & incorporates into a homologous chromosome

135
Q

Aneuploidy

A
  • When deletion/duplication occurs with entire chromosome

- Example: Down syndrome -> 3 copies of chromosome 21

136
Q

Polyploidy

A

When deletion/duplication occurs with sets of chromosomes

137
Q

Translocation Mutation

A
  • When a segment of DNA from 1 chromosome is inserted into another chromosome
  • can be caused by transposition
138
Q

Inversion Mutation

A
  • The orientation of a section of DNA is reversed on a chromosome
  • can be caused by transposition
139
Q

Transposition

A
  • takes place in prokaryotes and eukaryotes

- one mechanism by which a somatic cell of a multicellular organism can alter its genetic make up without meiosis

140
Q

Transposable Elements/Transposons

A
  • DNA fragments
  • can excise themselves from a chromosome & reinsert themselves at another location
  • can contain one gene, several genes, or just a control element
141
Q

Forward & Backward Mutations

A

Refer to an already mutated organism that is mutated again

142
Q

Forward Mutation

A

Changes the mutated organism even more from its original state

143
Q

Backward Mutation

A

Tending to revert the mutated organism back to its original state

144
Q

Wild Type

A

The original state

145
Q

MUTATION FLOW CHART

A
146
Q

Cancer

A

Unrestrained & uncontrolled growth of cells

147
Q

Tumor

A

Mass of cancer cells

148
Q

Proto-onco-genes

A

Certain genes that stimulate normal growth in human cells

149
Q

Oncogenes

A
  • Proto-onco-genes can be converted to oncogenes

- genes that cause cancer by mutagens such as UV radiation, chemicals, or random mutations

150
Q

Carcinogens

A

Mutagens that can cause cancer

151
Q

How long is all the DNA in a single cell when it is stretched out?

A

5 ft

152
Q

Histones

A
  • Globular proteins that sections of DNA that aren’t in use are wrapped tightly around
  • basicity of them gies them a net positive charge at normal pH of the cell
153
Q

Nucleosome

A
  • 8 histones wrapped in DNA

- Wrap into coils called solenoids, which wrap into supercoils

154
Q

Chromatin

A
  • The entire DNA/protein complex (including a very small amount of RNA)
  • 1/3 DNA by mass, 2/3 protein, small amount of RNA
  • when transcribed, it must be uncoiled
155
Q

Heterochromatin

A

Condensed chromatin

156
Q

Constitutive Heterochromatin

A

Permanently coiled chromatin

157
Q

Euchromatin

A
  • Chromatin that can be uncoiled & transcribed

- only coiled during nuclear division

158
Q

Order From Chromsome to Histone

A

Chromsome -> supercoil w/in chromosome -> coiling w/in supercoil -> chromatin fiber -> nucleosome w/in chromatin -> Histone & DNA w/in nucleosome

159
Q

Chromsomes

A
  • In nucleus of human somatic cell, there are 46 double stranded DNA molecules
  • The chromatin associated w/ each one of these molecules is called a chromosome
  • Each chromosome contains hundreds or thousands of genes
  • Before & after replication = 46 chromosomes in nucleus of human cells
  • The duplicates can be referred to separately as sister chromatids.
160
Q

Homologues

A
  • In human cells, each chromosome possesses a partner that codes for the same traits as itself, they are called homologues
  • Traits are the same, but actual genes may be different
161
Q

Diploid

A

Any cell that contains homologous pairs

162
Q

Haploid

A

Any cell that doesn’t contain homologues

163
Q

Cell Life Cycle (Somatic Cell of Multicellular Organism)

A
  • Divided into 4 stages:
    1. The first growth phase (G1)
    2. Synthesis (S)
    3. Second growth phase (G2)
    4. Mitosis or meiosis (m)
    5. Cytokinesis (c)
164
Q

Interphase

A

Collectively G1, S, & G2

165
Q

G1

A
  • Cell splits & begins to grow producing new organelles & proteins
  • Heterochromatin unwound & decondensed into euchromatin
  • RNA & protein synthesis are very active
  • Checkpoint @ end to see if conditions favorable for division
  • Normally the longest stage
166
Q

If the conditions are favorable in G1 phase, what phase does it enter?

A

S Phase

167
Q

If conditions are not favorable in G1 phase, what phase does it enter?

A

G0 phase

168
Q

What is the main factor triggering beginning of S phase from G1?

A

Cell size based upon ratio of cytoplasm to DNA

169
Q

G0

A
  • nongrowing state distinct from interphase
  • allows for the differences in length of the cell cycle
  • mature neurons & muscle cells remain in G0 permanently
170
Q

S Phase

A
  • energy devoted to replicating DNA
  • organelles & proteins produced more slowly
  • Each chromosome is exactly duplicated - by convention cell still considered to have same # of chromosomes, only now, each chromosome is made of 2 identical sister chromatids
171
Q

G2

A
  • Cell prepares to divide
  • organelles continue to duplicate
  • RNA & protein (esp. tubulin for microtubules) are actively synthesized
  • 10-20% of the cell life cycle
  • G2 checkpoint checks for mitosis promoting factor (MPF)
  • When level of MPF is high enough, mitosis is triggered
172
Q

Mitosis

A
  • Nuclear division w/o genetic change
  • 4 stages: Prophase, metaphase, anaphase, & telophase (PMAT)
  • Varies among eukaryotes
  • Results in genetically identical daughter cells
173
Q

Prophase

A
  • Characterized by condensation of chromatin into chromosomes
  • centrioles move to opposite ends of cell
  • First the nucleolus then the nucleus disappear
  • The spindle apparatus begins to form
174
Q

Spindle Apparatus

A
  • Aster: microtubules radiating from centrioles
  • Kinetochore microtubules growing from centromeres
  • Spindle microtubules connecting the 2 centrioles
175
Q

Centromeres

A

Group of proteins located toward center of chromosome

176
Q

Kinetochore

A

Structure of protein & DNA located at centromere of the joined chromatids of each chromosome

177
Q

Metaphase

A

Chromosomes align along equator of the cell

178
Q

Anaphase

A
  • Begins when sister chromatids split at their attaching centromeres & move toward opposite ends of cell
  • this split is termed disjunction
  • cytokinesis may commence toward the end of this phase
179
Q

Telophase

A
  • The nuclear membrane reforms followed by the reformation of the nucleolus
  • Chromosomes decondense
  • Cytokinesis continues
180
Q

Cytokinesis

A

Actual separation of cellular cytoplasm due to constriction of microfilaments about the center of the cell

181
Q

Meiosis

A
  • Double nuclear division that produces four haploid gametes or germ cells
  • In humans, only spermatogonium & oogonium undergo meiosis
  • All other cells are somatic & undergo mitosis only
182
Q

Primary Spermatocyte/Oocyte

A

After replication occurs in S phase of interphase, this is what cell is called

183
Q

Rounds of Meiosis

A
  • Meiosis I : Reduction Division

- Meiosis II

184
Q

Differences in Meiosis vs. Mitosis : Prophase I

A
  • Homologous chromosomes line up along side each other, matching their genes exactly
  • crossing over may occur
  • Each duplicated chromosome appears as an ‘x’, the side by side homologues exhibit a total of 4 chromatids & are called tetrads
  • If crossing over doesn’t occur, the 2 chromosomes are zipped along each other where nucleotides are exchanged, and form the synaptonemal complex
185
Q

Crossing Over

A
  • Exchange sequences of DNA nucleotides

- Genetic recombination may occur during crossing over

186
Q

Chiasma

A

‘x’ shape

187
Q

Linked

A

Genes located close together on a chromosome are more likely to cross over together

188
Q

Differences in Meiosis vs Mitosis: Metaphase I

A
  • Homologues remain attached and move to metaphase plate

- Rather than single chromosomes aligned along the plate as in mitosis, tetrads align

189
Q

Differences in Meiosis vs. Mitosis: Anaphase I

A

Separates homologues from their partners

190
Q

Differences in Meiosis vs. Mitosis: Telophase I

A
  • Nuclear membrane may or may not reform & cytokinesis may or may not occur
  • If cytokinesis occurs, the new cells are haploid with 23 replicated chromosomes, and are called secondary spermatocytes or oocytes
191
Q

Polar Body

A
  • In case of female, one of the oocytes, called the 1st polar body is much smaller & degenerates
  • occurs to conserve cytoplasm
  • 1st polar body may or may not undergo meiosis II, producing 2 polar bodies
192
Q

Meiosis II

A
  • Proceeds w/ prophase II, metaphase II, anaphase II, and telophase II
  • Final products: Haploid gametes each w/ 23 chromosomes
  • In case of oocyte, a single ovum is formed
  • In case of spermatocyte, four sperm cells are formed
  • In females, telophase II produces 1 gamete & a 2nd polar body
193
Q

Nondisjunction

A
  • If during anaphase I or II the centromere of any chromosome doesn’t split
  • Primary nondisjunction = in anaphase I
194
Q

Primary Nondisjunction

A
  • Results in one of the cells having 2 extra chromatids ( a complete extra chromosome), and the other will be missing a chromosome
195
Q

Secondary Nondisjunction

A

Results in one cell having 1 extra chromatid and one cell lacking 1 chromatid

196
Q

Nondisjunction in Mitosis

A

Nondisjunction can occur in mitosis but it is less severe b/c genetic info in new cells isn’t passed on to every cell in body

197
Q

DIAGRAM OF MEIOSIS

A
198
Q

Under the light microscope, metaphase in mitosis would appear like what in meiosis?

A

Metaphase II

Biology (4 decks)

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