Chapter 4 Study Guide

RNA and DNA have significant differences although both are nucleic acids. What are some of these differences?

-RNA is much smaller, ranging from about 70-90 bases and DNA averages more than 100 million base pairs long -The sugar in RNA is ribose instead of deoxyribose

What is happening during anaphase?

-centromeres divide in two -spindle fibers pull sister chromatids to opposite poles of cell -each pole (future daughter cell) now has an identical set of genes

What is happening during prophase?

-chromosomes condense and nuclear envelope breaks down -spindle fibers grow from centrioles -centrioles migrate to opposite poles of cell

What is happening during telophase?

-chromosomes gather at each pole of cell -chromatin decondenses -new nuclear envelope appears at each pole -new nucleoli appear in each nucleus -mitotic spindle vanishes

What is happening during metaphase?

-chromosomes lie along midline of cell -some spindle fibers attach to kinetochores -fibers of aster attach to plasma membrane

List some of the things mitosis is responsible for

-development of an individual, composed of some 50 trillion cells, from a one-celled fertilized egg -growth of all tissues and organs after birth -replacement of cells that die -repair of damaged tissues

Ribonucleic acid (RNA) is produced in three types. What are the 3 types?

1. messenger RNA (mRNA) 2. ribosomal RNA (rRNA) 3. transfer RNA (tRNA).

Mitosis has four phases: what are those four phases?

1. prophase 2. metaphase 3. anaphase 4. telophase

The minimum code to symbolize ______ amino acids is ___ nucleotides per amino acid.

20; 3

The 46 human chromosomes come in two sets of ______ each, one set from each parent.

23

The genetic code is a system that enables what?

4 nucleotides to code for the amino acid sequences of all proteins

The possible combinations of three bases would yield a maximum of _____ codons; therefore, some amino acids are specified by more than one codon

64

What is an example of a base pair?

A-T and C-G where there is an A on one backbone, there is normally a T across from it, and every C is normally paired with a G

When a cell is preparing to divide, it copies its entire nuclear ________. Each chromosome is made up of two _______ __________ that then coil further.

DNA; sister chromatids

Some cells cease to divide for days, years, or the rest of one's life; these are said to be in what phase?

G0 (G-zero) phase

What phase is an interval between cell division and DNA replication?

G1 (first gap phase)

What are the 4 main phases of the cell cycle?

G1, S, G2, M

During which phase does the cell finish replicating its centrioles and synthesizes enzymes that control cell division? It also checks replication for errors.

G2 (second gap phase)

The length of the cell cycle varies depending on what? Can you give some examples?

It varies greatly from one cell type to another Ex: stomach and skin cells divide rapidly, whereas bone and cartilage cells divide slowly

What phase is the period during which a cell replicates its nucleus and then pinches in two to form two new daughter cells?

M (mitotic phase)

What is interphase?

Phases G1, S, and G2 the time between M phases

What phase is the period during which the cell makes a duplicate copy of its centrioles and its entire nuclear DNA?

S (synthesis phase)

During the G1 phase the cell is doing what?

a cell synthesizes proteins, grows, and carries out its preordained tasks for the body

What does a nucleosome consists of?

a core particle (the spool of histones with the DNA ribbon around them) and a short segment of linker DNA leading to the next core particle

What is the cell cycle?

a life cycle of a cell extending from one division to the next

What is a base triplet?

a sequence of 3 DNA nucleotides that stands for one amino acid

What is a nucleosome?

a structural unit of a eukaryotic chromosome, consisting of a length of DNA coiled around a core of histones.

What two bases form two hydrogen bones with each other?

adenine and thymine

Define genome.

all the DNA, both coding and noncoding, in one 23-chromosome set

We now define a gene as what?

an information-containing segment of DNA that codes for the production of a molecule of RNA, which in most cases goes on to play a role in the synthesis of one or more proteins

An inability to stop cycling and enter the G0 phase is characteristic of what type of cells?

cancer cells

The essential function of DNA is to do what?

carry instructions, called genes, for the synthesis of proteins

DNA replication is necessary prior to ______ __________ and is accomplished through complementary base pairing.

cell division

In early cell division, a chromosome is what?

chromatids

Human chromatin consists of 46 long filaments called _______________

chromosomes

Messenger RNA contains a "mirror image" of each base triplet, and this group of three bases is called a ________.

codon

What is translation?

converts the language of nucleotides into the language of amino acids mRNA to protein

What is cytokinesis?

division of the cytoplasm into two cells

When a gene is activated, an ________ copy is made; this migrates to the cytoplasm where its code is "read" by a ___________.

exact; ribosome

What two bases form three hydrogen bonds with each other?

guanine and cytosine

The core particle is a disc-shaped cluster of eight proteins called ___________, with the DNA wound around it like ribbon around a spool.

histones

How does cytokinesis occur?

it is achieved by the motor protein myosin pulling on microfilaments of actin in the terminal web of the cytoskeleton. this creates a crease called the cleavage furrow around the equator of the cell

Cells divide by two mechanisms: mitosis and meiosis; __________ is restricted to production of eggs and sperm, and _________ serves all the other functions of cell division

meiosis; mitosis

What does the start codon code for?

methionine

DNA and other nucleic acids are composed of ____________, each of which is made up of a sugar, a phosphate group, and a nitrogenous base

nucleotides

Different cells have different active genes. A given cell uses only _______ to _________ of its genes.

one-third; two-thirds

Sister chromatids are joined at a ____________, which has a kinetochore on each side.

pinched spot called the centromere

DNA and RNA collaborate to make what?

proteins

What are the three bases that are pyrimidines? What are the two bases that are purines?

pyrimidines: cytosine (C), thymine (T), and uracil (U) purines: adenine (A) and guanine (G)

Define cleavage furrow.

the area where it pinches inward (when the cell splits in two)

What specifies which proteins a cell can make?

the genetic code in DNA

What is chromatin?

the material of which the chromosomes of organisms other than bacteria are composed. It consists of protein, RNA, and DNA.

What organelle is DNA packed into?

the nucleus

What is transcription?

the process of copying genetic instructions from DNA to RNA

Describe the structure of DNA. What is the backbone made up of?

the structure of DNA is commonly described as a double helix which resembles a staircase; each sidepiece is a backbone composed of phosphate groups alternating with the sugar deoxyribose

The code also contains stop codons, which end what?

they signal "end of message"; they enable the cell's protein-synthesizing machinery to sense that it has reached the end of the instruction for a particular protein

The classical concept of a gene was as an abstract "unit of heredity" by which a ______ passes to offspring.

trait