Transcript Cytoskeleton

Cytoskeleton
Microfilaments

Thinnest elements are composed of actin (a protein)

Most prevalent at periphery of cell

Two general functions
1.
Providing mechanical support

Basic strength and shape of cell

Anchor integral proteins

Support microvilli
2.
Helping generate movements

Muscle contraction

Cell division

Cell locomotion
1
2
Cytoskeleton
Intermediate filaments

Thicker than microfilaments but thinner than
microtubules

Several different proteins

Exceptionally strong

Found in parts of cells subject to mechanical
stress

Stabilize position of organelles such as nucleus

Help attach cells to one another
3
4
Cytoskeleton
Microtubules

Largest of cytoskeletal components

Long, unbranched hollow tubes

Composed mainly of tubulin (a protein)

Assembly begins in centrosome growing
outward into cell

Help determine cell shape

Involved in the movement of vesicles,
chromosomes, cilia, and flagella
5
6
Centrosome
Located near the nucleus
Consists of


Pair of centrioles


Pericentriolar material




Cylindrical structures with nine clusters of three
microtubules arranged in circular pattern
Hundreds of ring-shaped complexes composed of
tubulin
Organizing centers for growth of mitotic spindle in cell
division
Replicate during cell division
7
8
9
Cilia and Flagella
Cilia



Numerous, short, hair like projections
extending from surface of cell
Function to move fluid along cell surface
Flagella




Similar in structure to cilia, but much longer
Function to move entire cell
In humans, only found in sperm
10
11
12
13
14
15
Ribosomes
Sites of production of protein synthesis
Contain high content of RNA
Consists of two subunits
Made in nucleus








Large subunit
Small subunit
Some attach to endoplasmic reticulum
Free ribosomes produce proteins used in
cytosol
16
17
Endoplasmic Reticulum
Network of membranes
Rough ER





Continuous with nuclear envelope
Studded with ribosomes
Some proteins enter spaces in ER for processing
and sorting. Carbohydrates added to
glycoproteins.
Smooth ER




Lacks ribosomes
Contains unique enzymes that synthesize fatty
acids and steroids
Specialized function depending on location
18
19
Golgi Complex
Most proteins synthesized on rough ER
transported to other regions of cell
All pass through the Golgi complex
3-20 cisternae



Small flattened membranous sacs
Two surfaces




Entry face on rough ER surface
Exit face on plasma membrane surface,
functions in secretion.
20
21
22
Lysosomes
Membrane enclosed vesicles
Form from Golgi complex
Contain as many as 60 enzymes



Break down molecules
Help recycle worn out cell parts



Autophagy digestion of other organelles
Work best in acidic pH (~5)


Membrane pumps import hydrogen ions
keeping pH low
23
24
25
Mitochondria
Site of most ATP production
Numbers vary from hundreds to
thousands per cell
Double membraned organelle
Contains its own DNA





Can self replicate
Inner membrane characteristics




Inward folds are called cristae
Inner space called matrix
Cellular respiration reactions occur here
26
27
28
29
30
31
Concept 3.5
Nucleus
32
Nucleus
Usually most prominent feature of cell
A few cells have multiple nuclei but
most have only one
Have a double membrane



Outer membrane contiguous with rough ER
Openings in envelope called nuclear pores



Control movement of substances
33
Nucleus
Contains DNA







DNA has genes
Genes arranged along chromosomes
Humans have 46 chromosomes (23 pair)
Entire genetic information is called genome
Chromosomes are DNA coiled around
specialized proteins
Uncoiled DNA with its associated proteins
(histones) and RNA is called chromatin
34
35
36
37
38
39
40
Concept 3.6
Transcription and
Translation
41
Gene Expression





DNA is the blue print for RNA
RNA is the blue print for protein
Proteins determine the physical and chemical
characteristics of cells
Three RNA nucleotides (codon) code for a
particular tRNA (anticodon) which carries a
particular amino acid
Therefore, the sequence of DNA nucleotides
determines sequence of RNA nucleotides
which in turn determines the sequence of
amino acids
42
43
Transcription





DNA is the blue print for RNA
DNA stays in the nucleus, RNA is
transcribed from DNA and is mobile
mRNA strand is “read” by ribosomes
and signal for particular tRNAs carrying
specific amino acids
RNA polymerase is the enzyme catalyzes
transcription
Promoter sequence before coding region
44
Transcription
Base pairing
Sequence of RNA determined by base pairing:
DNA
RNA
Adenine
Uracil
Thymine
Adenine
Guanine
Cytosine
Cytosine
Guanine

Coding region of gene stops at terminator site
which signals enzyme to release

45
46
Translation






Nucleotide sequence is read by ribosome
Occurs in cytosol
Codon on mRNA signals for tRNA
carrying particular amino acid
Small subunit has binding site for
mRNA
Large subunit has two binding sites for
tRNA P site and A site.
See figure 3.26
47
48
49
50
51
52
53
54
55
Concept 3.7
Cell Division
56
Cell Division
Cytoplasmic division called cytokinesis
Somatic cell division




Produces two new identical cells
Nuclear division called mitosis
Reproductive cell division



Produces gametes with half as many
chromosomes as primary cell
Nuclear division two-step division called
meiosis
57
Somatic Cell Division
Cell cycle

Sequence of events that cell undergoes until
it divides
Cells with pairs of chromosomes are diploid
symbolized 2n
One member of each pair is inherited from
biological father and the other member is
inherited from biological mother





Pair are called homologues
Each one called homologous chromosome
58
Somatic Cell Division



Cell cycle
Interphase

G1

Cell is metabolically active replicates most
everything BUT its DNA (8-10 hours)

S phase

Cell duplicates its DNA (8 hours)

G2

Growth continues

Cell prepares for division

Replication of centrosomes completed
Cell now ready for mitotic phase
59
60
61
Mitotic Phase of Cell Cycle
Nuclear division followed by cytokinesis





Prophase
Metaphase
Anaphase
Telophase
See figure 3.30a, b, c, d, e
62
63
Cytokinesis




Process begins during anaphase
Formation of cleavage furrow
When complete two new identical cells
results
See figure 3.32
64
65
66
End Chapter 3
67