Week 2

Question 1

What happens in telophase in mitosis?

Answer 1

• Telophase begins after chromosmal movement stops. The identical sets of chromosomes at opposite neds of cell, uncoil and revert to threadlike chromatin form. - A nucelar enveloped forms around each chromatin mass, and nucleoli reappear in identical nuclei, and mitotic spindle preaks up. - Division of a cell’s cytoplasm and organelles into two identical cells is calle cytokinesis (usually begins in late anaphase, and is completed after telophase).

Question 2

What are the functions of the Golgi Complex?

Answer 2

• Modifies, stores, packages and transports proteins received from rough ER - Forms secretory vesicles that discharged processed proteins via exocytosis into extracellular fluid - Forms transport vesicles that carry molecules to plasma membrane & lyosomes

Question 3

What is the structure of the mitochondria?

Answer 3

• A mitochondria consists of an outer mitochondrial membrane and an inner mitochondrial membrane with a small fluid-filled space between them (similar to plasma membrane). - In inner mitochondrial membranes are series of folds called mitochondrial cristae that carries enzymes. These folds provide surface area for chemical reactions that produce ATP - Central fluid-filled cavity (enclosed by inner mitochondrial) is mitochondrial matrix

Question 4

What is cilia’s structure and function?

Answer 4

• Cilia are numerous, short, hair like projections that extend from surface of cell. - each cilium contains core of 20 microtubules surrounded by plasma membrane - coordinated movement of many cilia causes steady movement along cell’s surface - E.g. cells in respiratory tract have hundreds of cilia that help sweep foreign particles trapped in mucous away from lungs. Cells that line fallopian tubes sweep oocytes towards uterus.

Question 5

The cytoskeleton is a network of protein filaments that extends throughout the cytosol. Explain the 3 different types of filaments.

Answer 5

1. Microfilaments: - thinnest cytoskeleton - composed of actin and myosin proteins - most prevalent at edge of cell - Two general functions: generate movement (in muscle contraction, cell division, cell locomotion) and mechanical support. 2. Intermediate filaments: - thicker than microfilaments, thinner than microtubules - several different proteins compose intermediate filaments –> very strong - found in areas subject to mechanical stress - stabilise position of organelles (e.g. nucleus) and help attach cells to one another 3. Microtubules - largest cytoskeletal component - long, unbranched hollow tubes composed mainly of protein tubulin - grow outward from the centrosome towards periphery of cell - help determine cell shape, function in movement of organelles (secretory vesicles), chromosomes during cell division and make up specialised cell projections (cilia and flagella)

Question 6

What is the structure of centrosomes and what are its functions.

Answer 6

Located near nucleus, consists of two components: pair of centrioles and pericentriolar material. 2 centrioles are cylindrical structures, composed of 9 clusters of three microtubules in circular pattern. They lie perpendicular to each other. Pericentriolar material is composed of ring-shaped complexes of tubulin which are organising centres for grwoth of mitotic spindle, and mictrotubule formation in non-dividing cells.

Question 7

Interphase is when the cell produces additional organelles and cytosolic components in anticipation of cell division. What happens in the G1 Phase in inter phase

Answer 7

During G1, cell is metabolically active; it replicates most of its organelles and cytosolic components BUT NOT DNA - Generally lasts around 8-10 hrs for a cell with a cycle time of 24 hrs (total cell cycle time varies) - Cells that remain in G1 for a very long time (probably wont ever divide again) are said to e in G0 phase. Most nerve cells are in G0 phase

Question 8

A cell may have as few as a hundred or as many as several thousand mitochondria. Why do some cells have more mitochondria then others?

Answer 8

Active cells that use ATP at a high rate (such as those found in muscles, liver, kidneys) have large number of mitochondria. For example, regular exercise can increase the number of mitochondria in muscle cells, allowing them to function more efficiently.

Question 9

What is flagella’s structure and function?

Answer 9

• Structure similar to cilia (made of microtubules) but much longer - Move entire cell by foward motion along axis by rapidly wiggling - Only example in human body is sperm cell’s tail, which propels sperm towards oocyte in uterine tube

Question 10

What are somatic cells and germ cells?

Answer 10

Somatic cells (mitosis) are body cells of an organisms that do all the ‘daily’ functions of the organism. Germ cells (meiosis) are reproductive cells - eggs & sperm involved in starting the next generation.

Question 11

There are two distinct forms of the endoplasmic reticulum (ER). Explain the structure and function of the Rough ER. Also, fun fact. Moving molecules through the ER can be described as moving molecules through cisternal place from one part of the cell to another.

Answer 11

• Rough ER is continuous with nuclear membrane and usually folded into series of flattened sacs, - Outer surface is studded with ribosomes - Proteins synthesised (glycoproteins & phospholipids) by these ribosomes enter spaces within ER for processing and sorting. - Produces secretory proteins, membrane proteins, and many organellar proteins.

Question 12

What is the lipid bilayer?

Answer 12

Bilayer arrangement occurs because lipids are amphipathic molecules, which means that they have both polar and nonpolar parts. In phospholipids, the polar part is the phosphate-containing ‘head’, (hydrophilic) and the nonpolar parts are the two long fatty acid tails (hydrophobic hydrocarbon chains). The phospholipid molecules orient themselves in the bilayer with their hydrophilic heads facing outwards and the hydrophobic fatty acids facing inwards, forming a nonpolar hydrophobic region in the membrane’s interior.

Question 13

What are microvillie?

Answer 13

Minute, fingerlike extensions of plasma membrane that project from exposed cell surface. increases surface area of cell, therefore increases absorption.

Question 14

What is meiosis?

Answer 14

• Is a process where a single cell divides twice to produce four cells containing half the original amount of genetic information - Meiosis is the reproductive cell division that occurs in the gonad (ovaries & testes) - Produces haploid cells (single set of 23 chromosomes), becomes diploid after fertilisation - Unlike mitosis, meiosis occurs in two successive stages: meiosis I and meiosis II

Question 15

What happens in anaphase in mitosis?

Answer 15

During anaphase, centromeres split, separating two members of each chromatid pari, which move towards opposite cell. As the chromosomes are pulled by microtubules during anaphase, they appear V-shaped because centromeres lead the way, leaving trailing arms of chromosomes towards the pole

Question 16

What are some of the functions of the nucleus?

Answer 16

• controls cellular structure - directs activities of the cell - produces ribosomes in nucleoli - DNA is stored in nucleus

Question 17

What are some of the functions of the mitochondria?

Answer 17

• Referred to powerhouses of cell because they generate most of ATP through aerobic (oxygen requiring) respiration - Plays an important role in apoptosis (cell death). In response to stimuli (large numbers of destructive free radicals, DNA damage, growth damage, growth factor deprivation, lack of oxygen and nutrients), chemicals are released from mitochondria following formation of pore in outer mitochondrial membrane - Carriers genetic material - mtDNA inherited from mother- can track maternal lineage

Question 18

Explain structure and function of Smooth ER

Answer 18

• Extends from rough ER forming network of membrane tubules. Doesn’t have ribosomes - Doesn’t synthesis proteins but synthesises fatty acids and steroids (oestrogens and testosterone) - Smooth ER can inactivate or detoxify drugs, alcohol & other potentially harmful substances

Question 19

What makes up a lysosome?

Answer 19

• Membrane enclosed vesicles that form from Golgi complex - Contain many digestive and hydrolytic enzymes - lysomals interior is ph5, 100 times more acidic that pH of cytosol (pH 7)

Question 20

What is cancer essentially a disease of mitosis?

Answer 20

Normal checkpoints regulating mitosis are ignored/overridden by cancer cell. - Cancer begins when a single, normal cell is transformed into a cancer cell (often because a change in function of a gene that controls growth) - once crucial cell cycle genes act abnormally, cancer cells start to proliferate wildly by repeated, uncontrolled mitosis

Question 21

What is mitosis?

Answer 21

Mitosis (somatic cell division) is when a starting cell divides to produce two identical diploid cells. Has 4 stages, prophase, metaphase, anaphase, telophase.

Question 22

S phase is the interval between G1 and G2, lasts about 8 hours. What happens in S phase of interphase?

Answer 22

• DNA replication occurs. Its helical structure uncoils and two strands separate at points where hydrogen bonds connect base pairs. - Each exposed base of the old DNA strand then pairs its complementary base of newly synthesised nucleotide. - A new DNA takes shapes as chemical bonds form between neighbouring nucleotides. - Uncoiling and complementary base pairing contiues until there are tow identical DNA molecules

Question 23

What are the three main features of cells?

Answer 23

Plasma membrane: - forms cell’s flexible outer surface, separating internal environment from external environment - selective permeability - controls transport of substances in & out of cell - helps identify cell to other cells - participates in inter cellular signalling Cytoplasm: - consists of all cellular contents between plasma membrane and nucleus - compartment has two components: cytosol (intracellular fluid; contains dissolved solutes and suspended particles) and organelles Nucleus - large organelles that houses most of a cell’s DNA - within nucleus each chromosomes contains thousands of genes which control most aspects of cellular structure and function

Question 24

What are integral and peripheral membrane proteins?

Answer 24

Integral proteins are firmly embedded into the lipid bilayer and are commonly trans membrane proteins (span the entire lipid bilayer and protrude into both the cytosol and extracellular fluid). Peripheral membrane proteins are membrane proteins that adhere only temporarily to the biological membrane with which they are associate.

Question 25

G2 lasts 4 to 6 hrs. What happens in G2 phase?

Answer 25

During G2, cell growth continues, enzymes and other proteins are synthesised in preparation for cell division, replication of centrioles is complete. - At the end of this phase is the G2M checkpoint, when the cell is checked to see if all DNA is replicated, if so the cell is ready to divide - Errors in DNA replication may result in mutations or development of cancer

Question 26

Discuss what chromosomes are.

Answer 26

• Human cells, contain 23 pairs of chromosomes (one originally from mum and dad) - Each chromosome contain a few thousand genes that code for all cellular proteins - The two chromosomes that make up each pair are called homologus chromosomes because they contain similar genes arranged in the same order; generally look very similar, except for sex chromosomes (female xx, male xy) - Centromere holds the chromatin pair together, outside each centromere is a kinetochore (protein complex)

Question 27

What is the fluid mosaic model?

Answer 27

According to this model, the molecular arrangement of the plasma membrane resembles a continually moving sea of fluid lipids that contains a mosaic of many different proteins. Some proteins float freely like icebergs in the lipid sea, whereas others are anchored at specific locations like islands.

Question 28

What happens in Metaphase in mitosis?

Answer 28

Microtubules of mitotic spindle aligh centromers of chromatid pairs at the exact centre of mitotic spindle.

Question 29

Explain how ribosomes are formed and their functions.

Answer 29

• Ribosomes are sites of protein synthesis - Strutually contains 2 subunits, one half the size of the other - Large and small subunits made separately in the nucleolus. Once made, both parts leave nucleus separately and come together in cytoplasm - some attach to outer surface of nuclear membrane, or Rough ER - Others are free, unattached to other cytoplasmic structures, and make proteins used in cytosol - There are also ribosomes that make mitochondrial proteins in the mitochondria

Question 30

What is the structure of the Golgi Complex?

Answer 30

• Consists of 3-20 cisternae (which are small, flattened membranous saces with bulging edges, often curved)\ - Convex entry (cis) face is a cisterna that faces the rough ER - Concave exit (trans) face is a cisterna that faces the plasma membrane - Sacs between entry and exist faces are medial cisternae - Transport vesicles from ER merge to from the entry face - From entry face, cisternae mature, in turn becoming medial and then exit cisternae

Question 31

What are the functions of lysosomes?

Answer 31

• Digestion: digests substances that enter cell via endocytosis and transport of final products digestion into cytosol - Removal: remove damaged or worn-out organelles by autophagy - Self-destruction - carry out autolysis, digestion of entire cell - accomplish extracellular digestion

Question 32

What is the structure of a nucleus?

Answer 32

• Nuclear envelope (double membrane) separates nucleus from cytoplasm - Both layers of nuclear envelop are lipid bilayers (like plasma membrane) - outer membrane of nuclear envelope is continuous with rough ER - have nuclear pores which controls movement of substance between nucleus and cytoplasm -

Question 33

What happens in the prophase stage of mitosis?

Answer 33

• In early prophase, chromatin fibres condense and shorten to prevent entangling of long DNA strands when they move. - Later, tubulin in centrosomes form mitotic spindle that attach to kinetochore (protein complex that is outside of each centromere (centromere holds chromatid pair together)) and push centrosomes to ends of cell, so the spindle extends from pole to pole - Then, nucleolus disappears and nuclear envelope breaks down

Question 34

What is a haploid?

Answer 34

• Indicates that a cell has only ONE copy of each chromosome - necessary for process of sexual reproduction - e.g. human egg is haploid (23 chromosomes) and sperm is haploid (23 chromosomes)