chapter 3 cell structure and genetic control

Describe the phases of the cell cycle, and explain how this cycle may be regulated.

During interphase, the cell grows, accumulating nutrients needed for mitosis, preparing it for cell division and duplicating its DNA. During the mitotic phase, the chromosomes separate. During the final stage, cytokinesis, the chromosomes and cytoplasm separate into two new daughter cells.Positive Regulation of the Cell Cycle. Two groups of proteins, called cyclins and cyclin-dependent kinases (Cdks), are responsible for the progress of the cell through the various checkpoints. ... Cyclins regulate the cell cycle only when they are tightly bound to Cdks.

Define the terms genome and proteome, and explain how they are related.

A genome is the complete set of genetic information in an organism. a proteome is the entire complement of proteins that are or can be expressed by a cell, tissue, or organism. Within an individual organism, the genome is constant, but the proteome varies and is dynamic. Every cell in an individual organism has the same set of genes, but the set of proteins produced in different tissues differ from one another and are dependent on gene expression

Describe the structure of nucleosomes, and explain the role of histone proteins in chromatin structure and function.

A nucleosome is a basic unit of DNA packaging in eukaryotes, consisting of a segment of DNA wound in sequence around eight histone protein cores. This structure is often compared to thread wrapped around a spool. Dimers have two histones, and tetramers have four histones. Each nucleosome has two identical dimers, each comprised of one H2A and one H2B histone. This is called an H2A-H2B dimer. Histones are alkaline (basic pH) proteins. They are found inside the nucleus of eukaryotic cells. Their function is to package DNA into structural units called nucleosomes. Histones are the main proteins in chromatin. Chromatin is a combination of DNA and protein which makes up the contents of a cell nucleus. Because DNA wraps around histones, they also play a role in gene regulation.

Distinguish between oncogenes and tumor suppressor genes, and give examples of how such genes may function.

An oncogene is a gene that has the potential to cause cancer. "bad" gene that can become permanently turned on or activated when it is not supposed to be. When this happens, the cell grows out of control, which can lead to cancer. Tumor suppressor genes are normal genes that slow down cell division, repair DNA mistakes, or tell cells when to die (a process known as apoptosis or programmed cell death). When tumor suppressor genes don't work properly, cells can grow out of control, which can lead to cancer. An important difference between oncogenes and tumor suppressor genes is that oncogenes result from the activation (turning on) of proto-oncogenes, but tumor suppressor genes cause cancer when they are inactivated (turned off).

Define apoptosis and explain the physiological significance of this process.

Apoptosis is a process that occurs in multicellular when a cell intentionally "decides" to die. This often occurs for the greater good of the whole organism, such as when the cell's DNA has become damaged and it may become cancerous. ... Apoptosis plays a role in causing and preventing some important medical processes.

Explain the functions of centrioles in nondividing and dividing cells.

In a dividing cell the centrioles divide themselves into two, one centriole on each side of the cell. At their respected sides the filaments then start to pinch off/ divid the current cell into two. In a nondividing cell, the centrosome migrate towards the outer portion the the cell cytoplasm and organize the production of a nonmotile primary cilium.

Describe the cell cycle using the proper symbols to indicate the different stages of the cycle

Interphase -G1: centrioles replicate -S: DNA replication -G2: final growth and activity before mitosis

Describe what is meant by epigenetic inheritance, and explain its significance.

It refers to external modifications to DNA that turn genes "on" or "off." These modifications do not change the DNA sequence, but instead, they affect how cells "read" genes. Examples of epigenetics. Epigenetic changes alter the physical structure of DNA. inheritance of traits transmitted by mechanisms not directly involving the nucleotide sequence. for example the "lick your rat" lab, schizophrenia in twins, or cancer

Describe the functions of lysosomes and peroxisomes.

Lysosomes are found in the cytoplasm of both plant and animal cells. It is a sac-like structure surrounded by a single membrane that holds very powerful digestive enzymes. Its function is to break down dying cells, organelles, toxins, and food particles. They are small organelles found in the cytoplasm of both animal and plant cells. The structure of peroxisomes is a membrane-bound organelle. They participate in the metabolism of fatty acids and have enzymes that get rid of toxic peroxides.

Distinguish between mitosis and meiosis, describe the phases of meiosis, and explain its functional significance.

Mitosis is responsible for reproducing somatic cells and meiosis is responsible for reproducing germ cells. The first is the condensation of chromatin into chromosomes that can be seen through the microscope; the second is the synapsis or physical contact between homologous chromosomes; and the crossing over of genetic material between these synapsed chromosomes.

Explain the process of exocytosis.

Molecules for export are packaged by the Golgi complex into vesicles. The vesicle walls fuse with the plasma membrane, adding to the surface area, while expelling their contents. This balances out the quantity lost during endocytosis.

Describe the different ways that cells can engulf materials in the extracellular fluid.

Phagocytosis: pseudopods are extended from the cell to wrap around invading organisms or extracellular debris in an amoeboid movement. Pseudopods join together and fuse around the victim. Once continuous, it pinches off into a food vacuole to later fuse with a lysosome. It is sometimes triggered by "eat me" signals of dying cells. Endocytosis: Pinocytosis: The plasma membrane furrows inward, and the membrane near the furrow edges fuses, creating a vesicle inside the cell. Endocytosis: Receptor-mediated Endocytosis: Specific molecules in the EC fluid with specific receptor proteins cause the membrane to invaginate/fuse/pinch off.

Describe the structure of the plasma membrane.

Plasma membranes (in cells and organelles) are composed of proteins and a double layer of phospholipid molecules, in which the nonpolar layers are sandwiched between the polar layers. Peripheral and integral proteins are embedded in the fluid-mosaic of the membrane, as well as lipids and carbs.

List the phases of mitosis and briefly describe the events in each phase

Prophase is the first phase is when the two sister chromatids pair up and the nucleoli disappears. Prometaphase is the second phase where the microtubules begin to separate from each other, each pair of microtubules attach to the kinetochores and some nonkinetohore microtubules interact with those from the opposite pole of the spindle. Metaphase is the third phase where the chromosomes are lined up on the invisible line of the metaphase plate. Anaphase is the fourth phase where the two daughter chromosomes begin to separate from each other to opposite poles. Telophase is the last phase where the two daughter nuclei form creating two identical nuclei.

Explain how precursor mRNA is modified to produce mRNA.

Regions of the pre-mRNA are spliced out, called introns. The exons are spliced together and form the mRNA.

Explain the interrelationship between the endoplasmic reticulum and the Golgi complex. What becomes of vesicles released from the Golgi complex?

Secretory proteins move from the endoplasmic reticulum to the Golgi complex. The Golgi complex then modifies these proteins and separates different proteins, and packages them in vesicles. Vesicles from the Golgi complex fuse with the plasma membrane and release their products by exocytosis.

Explain how RNA is produced within the nucleus according to the information contained in DNA.

The DNA is unwound by RNA polymerase and RNA is produced from the complementary base pairing of one strand of DNA. When the RNA is done transcribing, it splices out the introns and sends the mRNA into the cytoplasm.

What is the genetic code, and how does it affect the structure and function of the body?

The genetic code is the code our body uses to convert the instructions contained in our DNA the essential materials of life. It is typically discussed using the "codons" found in mRNA, as mRNA is the messenger that carries information from the DNA to the site of protein synthesis.Everything in our cells is ultimately built based on the genetic code. Our hereditary information - that is, the information that's passed down from parent to child - is stored in the form of DNA. That DNA is then used to build RNA, proteins, and ultimately cells, tissues, and organs.

Describe the structure and function of ribosomes.

a minute particle consisting of RNA and associated proteins found in large numbers in the cytoplasm of living cells. They bind to messenger RNA and transfer RNA to synthesize polypeptides and proteins. Ribosomes are a cell structure that makes protein. Protein is needed for many cell functions such as repairing damage or directing chemical processes. Ribosomes can be found floating within the cytoplasm or attached to the endoplasmic reticulum. Ribosomes consist of two major components: the small ribosomal subunits, which read the RNA, and the large subunits, which join amino acids to form a polypeptide chain. Each subunit comprises one or more ribosomal RNA (rRNA) molecules and a variety of ribosomal proteins (r-protein or r-Protein)

Describe the structure and functions of mitochondria

an organelle found in large numbers in most cells, in which the biochemical processes of respiration and energy production occur. It has a double membrane, the inner layer being folded inward to form layers (cristae) Supplies energy to a cell by releasing the energy stored in food molecules. The outer membrane surrounds a highly folded inner membrane where the chemical activity occurs.

Define apoptosis and explain its significance

cellular death in which the cells show characteristic histological changes. It occurs as part of programmed cell death and other events in which cell death is a physiological response.It has a role in biological processes, including embryogenesis, ageing, and many diseases The molecular mechanisms involved in death signals, genetic regulation, activation of effectors have been identified

Describe the appearance and composition of chromatin and the structure of nucleosomes. Comment on the significance of histone proteins.

chromosomes contain DNA(deoxyribonucleic acid) bound proteins called histones, which serve to package the dna and there by controls its functions. nuclear chromosomes are packaged by protein into a condensed structure called chromatin, so that the elongated dna molecule can fit into the nucleus. chromosomes contain dna and protein. the basic amino acids present in histones are lysine and arginine that impart positive charge to their structure at cellelar ph. the interaction between the positively charged histones and negatively charged phosphate groups of DNA and the intra-histone interactions from bead like structures called nucleosomes. nucleosomes consist of 146 DNA base pairs that wound around a histone protein core. nucleosomes contain protein called histone and dna base pairs. they are the dna packaging units that help to put genetic material intact. these nucleosomes are present during both mitosis and melosis.

Describe the structure and function of cilia, flagella, and microvilli.

cilia and flagella are the elongated motile structures of some cell surfaces, which are composed of microtubules. so, structurally both cilia and flagella are similar, but they differ in their length and abundance. Cilia: are the hair like projections present on the internal free surfaces of some organs like respiratory tract, intestine etc. these cilia move to and from to produce wave motion. these wave motion helps in the clearance excess mucous and fluids in various tracts and example, respiratory tract. flagella: are the elongated motile structures of some cell surfaces, which are composed of microtubules. they are needed for the locomotion of the organism. they consist of microtubules arranged in 9+2 array. the microtubules slide along one another and produce whip like motion. the best example is tail of sperm is a flagellum, which make the sperm swim along the female reproductive tract. sperm cells are the only example of cells with flagellum in human microvilli are the fold present on the cell surface, which increase the surface area and allow rapid diffusion across the membrane. for example the microvilli in the small intestine allow the rapid diffusion of substance, thus, promoting the absorption.

Draw a simple diagram of the semiconservative replication of DNA using stick figures and two colors.

during cell division, the replication of deoxyribonucleic acid (DNA) occurs, which is nothing but duplication of chromosomes. Dna replication result in the formation of two DNA helices. the semiconservative patterns of dna replication is demonstrated by meselson and stahl . in this, each strand of parent DNA act as template for the new strand, thus producing two new DNA strands. so the new formed dna contains one old strand and one new strand

Distinguish the two types of endoplasmic reticulum and explain the relationship between the endoplasmic reticulum and the Golgi complex.

rough endoplasmic reticulum (rough ER) and smooth endoplasmic reticulum (smooth ER). Both types are present in plant and animal cells. The two types of ER often appear as if separate, but they are sub-compartments of the same organelle. Cells specialising in the production of proteins will tend to have a larger amount of rough ER whilst cells producing lipids (fats) and steroid hormones will have a greater amount of smooth ER. Endoplasmic reticulum and Golgi apparatus are two membrane-bound organelles found in eukaryotes. Both these organelles are closely associated and functionally related. Both endoplasmic reticulum (ER) and Golgi apparatus are two components of the endomembrane system of a cell.

Give some specific examples that illustrate the dynamic nature of the plasma membrane.

the plasma membrane is a phospholipid bilayer which has a hydrophilic end and a hydrophobic end. It's constantly changing and is what allows certain things to enter the cell via a selectively permeable membrane

Why may tRNA be considered the "interpreter" of the genetic code?

the transfer RNA