30+ Cellbio

Front 1

Mendel’s Key Findings

Back 1

A. Each trait or phenotype is governed by a unit of inheritance (a gene).
B. Each pea plant possesses 2 copies of each gene.
C. Genes come in different versions (alleles).
D. One allele can be dominant over another allele.
E. Each adult pea plant carries two copies of each gene, but each reproductive cell (gamete)
contains only one copy of the gene for each trait: Mendel’s principle of segregation
F. Genes for different traits are inherited independently: Mendel’s principle of independent assortment

Front 2

Edouard van Beneden/ August Weismann

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idea of reductional division.
i. Cells of adult Ascaris worms have 4 chromosomes.
ii. Cells of worm gametes only have 2 chromosomes.

Front 3

Walter Sutton

Back 3

i. Chromosomes come in pairs (homologous chromosomes).
ii. During meiosis (the process by which gametes are formed) each gamete receives
only one of the homologous chromosomes. – very similar to Mendel’s ideas
about genes...

Front 4

Summary of similarities between Mendel’s “genes” and chromosomes

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A. Adults have 2 copies of each gene – & 2 copies of each chromosome
B. Gametes have only one copy of each gene -- & only one copy of each chromosome
C. Genes assort independently – different chromosomes assort independently...

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Nuclear envelope

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is a double membrane (2 parallel lipid bilayers), permeated by several
thousand protein-dense pores (nuclear pores)

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Nucleoli

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regions of the nucleus where ribosomal RNAs are being synthesized, and
ribosomal subunits are being assembled (but not intact ribosomes)

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Nucleoplasm

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the “fluid phase” of the interior of the nucleus (but protein concentration is
very high, as high as 100 mg/ml)

Front 8

Nuclear matrix

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fibrillar network of proteins crisscrossing the nuclear space

Front 9

Hutchinson-Gilford Progeria

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disease causing premature aging due to mutation in nuclear lamin A which allows easy deformation of nucleus.(nuclear lamina helps maintain the shape of the nucleus)

Front 10

nucleoporins

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make up nuclear pores; most extend into cytoplasm and nucleoplasm

Front 11

Nuclear localization sequences

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A. In order to enter the nucleus, a protein must have a nuclear localization sequence
(NLS, a cluster of basic, positively charged amino acids).
B. Mutations in NLS can prevent targeting to the nucleus.
C. The activity of some NLS can be regulated by other factors, such cytoplasmic Ca++.

Front 12

Ran Guanine Exchange Factor (Ran-GEF)

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in the nucleus, exchanges GDP for GTP

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Ran GTPase Activating Protein (Ran-GAP)

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in the cytoplasm, dephosphorylates GTP to GDP.

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“lampbrush” chromosomes

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c. Looped domains are also visualized in “lampbrush” chromosomes – meiotic chromosomes
that become partially unpacked to facilitate gene expression during a pause in
meiosis...a clue that gene expression and the level of DNA packaging may be inversely
related.

Front 15

Summary of DNA packaging levels

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a. supercoiled DNA is wound around core nucleosome particles to form 10 nm filament
b. the 10 nm filament is further packaged into a 30 nm fiber.
c. the 30 nm fiber is bundled into looped domains
3
d. looped domains are further
stacked and bundled onto a protein
scaffold; DNA is most highly
packaged when it condenses during
mitosis (or meiosis)

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euchromatin

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partially
unpacked, associated with regions of the genome that are being expressed

Front 17

constitutive heterochromatin

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highly packed, found in all cells at all stages of
development, associated mostly with non-coding, centromeric DNA

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facultative heterochromatin

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highly packed, differs from cell type to cell type and
with developmental stage; associated with regions of the genome that contain
genes that are not being expressed

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Barr body

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special type of facultative heterochromatin; consists of one entire X
chromosome in female mammals that has been inactivated.

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Rett syndrome

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is caused by mutations in a gene, MeCP2, that resides on the X chromosome;
almost all patients are females that are heterozygous for mutant MeCP2. The pattern
of X inactivation in the brain determines the severity of the disease

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epigenetic

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heritable traits that do not depend on DNA
sequence

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Telomeres

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are special repeated sequence that occur at the ends of chromosomes; they can
be visualized with a fluorescent DNA probe that hybridizes (by base pairing) specifically
to the characteristic repeated sequence.

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Centromeres

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b. Are composed of repeated sequence called alpha-satellite DNA
c. Contain an alternate histone called CENP-A instead of H3A
d. CENP-A functions in the attachment of the mitotic spindle, the microtubule based structure
that divides the chromosomes into two daughter cells during mitosis.

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snRNA

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components of spliceosomes that remove introns from mRNAs

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snoRNA

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components of ribonucleoproteins (RNPs) that process rRNA

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miRNA

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regulate mRNA translation and stability, regulate chromatin packing also

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siRNA

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function in destruction of foreign RNAs, are derived from foreign RNA (viral genome)

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Ribosome components

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60S (49 proteins, 3 rRNA, 28S, 5.8S, and 5S), 40S (33 proteins, 1 rRNA, 18S

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Nucleolus

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site of rRNA synthesis and ribosomal subunit assembly, visualized using GFP, rRNA genes organized into repeats,

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Nucleolus structure

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fabrillar center (feathery structures present),
dense fibrillar component and a granular component

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Moderately repeated fractions

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i. coding sequences – rRNA and histone genes
ii. non-coding sequences – transposable elements (LINE & SINE)

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a. Highly repeated fractions (~10% of the genome)

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i. alpha-satellite DNA (centromeric repeats)
ii. mini and micro-satellite DNA – polymorphic, can be used to study differences between
individuals and ethnic groups

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Non-repeated fractions

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includes all single copy genes; protein-coding part of human
is less than 2% of the total.