Chapter 9- DNA determines the structure and function of cells

Question 1

define DNA

Answer 1

short for deoxyribonucleic acid, is found in the cells of all organisms and contains genetic information which determines the structure of the cell and the way it functions.

Question 2

where are most DNA molecules found?

Answer 2

in the nucleus of the cell and are therefore called nuclear DNA.

Question 3

what is mitochondrial DNA?

Answer 3

this is the small amount of DNA that is found in the mitochondria (mtDNA).

mtDNA makes up less than 1% of the DNA found in humans.

Question 4

what are the two main types of nucleic acid found in the body?

Answer 4

DNA and RNA.

Question 5

explain the structure of DNA

Answer 5

DNA is a polymere, a molecule made up of many repeating small units. the small repeating units are called nucleotides.

Each nucleotide is composed of a sugar molecule (deoxyribose in DNA), a phosphate group and a nitrogenous base. There are 4 different nitrogenous bases in DNA; adenine, thymine, guanine and cytosine.

The sugar molecule of one nucleotide bonds to the phosphate group of another, forming a long chain of alternating sugars and phosphates, with side chains of bases.

Question 6

in DNA how do strands join

Answer 6

by specific bases being attracted to each other by weak hydrogen bonds. the two strands of DNA twist into a spiral shape called double helix.

Question 7

what determines genetic code?

Answer 7

the order in which nitrogenous bases occur in the DNA molecule.

a code of only 4 letters would not seem to allow many different combinations, but each gene consists of up to 2 million pairs of bases.

Question 8

how long is a DNA strand in humans?

Answer 8

estimated between 2-3 metres.

Question 9

what are DNA strands wrapped around?

Answer 9

a group of eight special proteins called histones to form a nucleosome.

Question 10

define histone

Answer 10

a special protein around which DNA is coiled to form chromatin

Question 11

explain the difference between chromatin in a non-dividing and dividing cell

Answer 11

in a non-dividing cell, the coiled DNA forms a tangled network called chromatin.

in a dividing cell the coiled chromatin becomes even more tightly coiled, becoming ‘super-coiled’ structures called chromosomes.

Question 12

how many chromosomes are in a normal human cell?

Answer 12

46

Question 13

what are chromosomes made up of?

Answer 13

each chromosome is made up of sections of DNA that code for particular protein.

each of these sections is called a gene.

Question 14

what are some important differences between DNA found in the nucleus and mtDNA?

Answer 14

nuclear DNA is in the form of very long strands that are bound to proteins, the histones.

mtDNA is in the form of small circular molecules that are not bound to proteins.

mtDNA is passed from mother to offspring and nuclear DNA is a combination of both the mother and father.

Question 15

how many molecules of mtDNA are found in each mitochondrion?

Answer 15

10

Question 16

explain genes within mtDNA

Answer 16

it has 37 genes, all essential for the function of mitochondrion.

24 of the genes contain the code for making transfer RNA (tRNA) molecules, which are involved in protein synthesis.

the remaining 13 genes contain instructions for making some of the enzymes necessary for the reactions of cellular respiration.

Question 17

explain DNA replication

Answer 17

the first stage is when the two strands of the DNA molecule are separated by the enzyme helicase. each strand of the separated section contains half he original information. each strand serves as a template for the nucleotides that will form the new strand.

As the base adenine can only pair with thymine and the base cytosine can only pair with guanine, the new strand that forms is identical to the original.

Question 18

what two enzymes are important in DNA replication?

Answer 18

DNA polymerase - enzyme that joins nucleotides together

DNA ligase - enzyme that joins the short sections of DNA together

Question 19

what is protein synthesis

Answer 19

the formation of DNA in the cell

instructions for protein synthesis are provided by genetic code

Question 20

what controls the order of amino acids?

Answer 20

the sequence of bases in DNA controls the order of amino acids, and therefore the type of protein that is produced.

Question 21

what is RNA?

Answer 21

RNA stands for ribonucleic acid and it is another type of nucleic acid.

like DNA, RNA is composed of a chain of nucleotides.

Question 22

outline four differences between RNA and DNA

Answer 22

1. the sugar molecule is ribose, not deoxyribose. ribose has one more oxygen atom than deoxyribose.
2. RNA is single stranded, while DNA is double stranded.
3. RNA has bases cytosine, guanine, adenine and uracil. the structures of thymine and uracil are very similar, meaning that uracil is complementary to adenine.
4. the RNA strand is able to fold onto itself, forming hydrogen bonds between complementary bases.

Question 23

what are the different types of RNA?

Answer 23

messenger RNA (mRNA)

Ribosomal RNA (rRNA)

Transfer RNA (tRNA)

Question 24

what is messenger RNA’s (mRNA) role in protein synthesis?

Answer 24

mRNA is made in the nucleus and takes the genetic code into the cytoplasm allowing the genetic code to be ‘read’ by ribosomes.

Question 25

what is ribosomal RNA's (rRNA) role in protein synthesis?

Answer 25

rRNA makes up approx. 60% of the mass of ribosomes, with the other 40% being protein. the rRNA ensures the correct alignment mRNA, tRNA and ribosome. it also has an enzymatic role in the formation of peptide bonds between amino acids.

Question 26

what is transfer RNA's (tRNA) role in protein synthesis?

Answer 26

tRNA is a small molecule of RNA, containing only 70-90 nucleotides. each tRNA is able to carry specific amino acid and therefore provides a vital role in protein synthesis.

Question 27

what determines the proteins that are produced

Answer 27

the sequence of bases

Question 28

provide examples of base sequences and the proteins they produce

Answer 28

CAG codes for amino acid valine TTA codes for leucine CCC codes for proline

Question 29

define transcription

Answer 29

the process by which the genetic instructions are copied (transcribed) from the DNA to the mRNA molecule.

Question 30

what is the transcription triggered by?

Answer 30

by chemical messengers that enter the nucleus from the cytosol and bind to the DNA at the relevant gene.

Question 31

what happens when the transcription is triggered?

Answer 31

it causes an enzyme called RNA polymerase to begin the process of making mRNA.

Question 32

explain the 5 steps of transcription

Answer 32

1. DNA unzips and RNA polymerase attaches to the template strand at a 'start' command. 2. RNA polymerase reads one triplet at a time, adding complementary nucleotides to form codons (uracil instead of thymine). 3. A 'stop' command (ATT) is reached and RNA polymerase detaches. 4. Newly formed mRNA strand detaches from the template strand and exists through nuclear pores. 5. DNA ligase reforms weak hydrogen bonds when the specific DNA is no longer needed.

Question 33

explain the 4 steps of translation

Answer 33

1. mRNA enters the cell cytosol and is attached to a ribosome. 2. The ribosome reads a codon at a time and recruits the tRNA molecule with the complimentary anticodon. 3. The tRNA molecule carries an amino acid, which forms a peptide bond with the AA before it. 4. The chain of peptides detaches and folds in a particular way to form a protein.

Question 34

define the cells cycle

Answer 34

the events that take place from one cell division to the next.

Question 35

what phases does interphase include?

Answer 35

G1 phase, S phase and G2 phase

Question 36

what is G1 phase?

Answer 36

the first growth stage. the cell produces new proteins, grows and carries out its normal tasks for the body. this phase ends when the cells DNA begins to duplicate.

Question 37

what is S phase?

Answer 37

synthesis phase. the DNA molecules in the cell nucleus form exact copies of themselves.

Question 38

what is G2 phase?

Answer 38

the second growth phase. short phase where the cell prepares for division.

Question 39

what is mitotic phase and what phases does it include?

Answer 39

when the cell divides into two daughter cells. it includes: - prophase - metaphase - anaphase - telophase

Question 40

explain the 5 events in prophase

Answer 40

1. nuclei disappear 2. nuclear membrane breaks down 3. centrioles migrate to opposite poles 4. chromosomes appear as pairs of chromatids 5. spindle fibres form

Question 41

explain the 2 events in metaphase

Answer 41

1. chromosomes line up at the equator of the cell | 2. the centromere of each pair is attached to a spindle fibre

Question 42

explain the 2 events of anaphase

Answer 42

1. centromeres divide | 2. chromosomes move to opposite ends of the spindle

Question 43

event the 5 events of telophase

Answer 43

1. spindle disappears 2. nuclear membranes and nucleoli form 3. centrioles divide 4. chromosomes uncoil and disappear 5. cytokinesis begins

Question 44

define mitosis

Answer 44

the division of a nucleus of a cell in which the two daughter nuclei have the same number and type of chromosomes as the parent nucleus.

Question 45

what is differentiation?

Answer 45

the process by which cells become specialised. as cells undergo division by mitosis, different genes become activated, making the cells differentiate into specialised cells that can perform particular functions.

Question 46

examples of specialised cells

Answer 46

stomach cells that can secrete enzymes. muscle cells that can contract. red blood cells that can carry oxygen.

Question 47

what are stem cells?

Answer 47

all cells that undergo cell differentiation are known as stem cells. they're not specialised for any role and can undergo repeated division through mitosis. in right conditions, they can differentiate into specialised cells.

Question 48

what do stem cells have the potential to do?

Answer 48

to develop into any cell type, meaning they could possibly provide an unlimited source of cells for repair of tissues such as bone, skin, muscle, liver or blood.

Question 49

explain stem cell classification

Answer 49

stem cells can be classified based on where they originate or the type of cells they form. totiponent - eg the early embryo before the formation of the inner cell mass. (first group of cells in an embryo that can go on to form any cell). pluripotent - eg the inner cell mass of an embryo. (creates all the tissues for the body). multipotent - eg embryonic stem cells, adult stem cells, cord blood stem cells.

Question 50

what is gene expression?

Answer 50

the process of copying information from DNA onto mRNA and then translating the message into a series of amino acids to form a protein.

Question 51

in reference to gene expression, what do genes contain?

Answer 51

instructions for making mRNA, but at any given time a cell is making mRNA from only a fraction of its genes. eg genes for the production of insulin are activated in some cells in the pancreas but not in bone or muscle cells.

Question 52

what are some factors that determine whether a gene is being expressed (whether it's on or off)?

Answer 52

- age of the cell - time of day - signals from other cells - environment of the cells - whether or not the cell is dividing

Question 53

what is DNA replication?

Answer 53

DNA producing an exact copy of itself.

Question 54

what is chromatin?

Answer 54

the tangled network of DNA in the nucleus of a cell that isn't dividing.

Question 55

explains ways that gene expression can modify the way in which DNA is wrapped around the nucleus

Answer 55

by changes in the amino acids of histone proteins, modifying the shape of the histone or DNA molecule remodelling.

Question 56

what are some histone modifications?

Answer 56

acetylation = the addition of an acetyl group to the histone protein. acetylation enhances gene expression. methylation = the addition of methyl groups to DNA. it inhibits gene expression by restricting access to RNA polymerase.

Question 57

what is epigenetic's?

Answer 57

some of the factors that make genes more or less likely to be expressed are inherited.

Question 58

a persons genome vs epigenome

Answer 58

genome = the heredity information encoded in their DNA. epigenome = the sum of all factors that determine when, where and which genes are 'switched on'.