chapter 13

Question 1

genes

Answer 1

sections of DNA that contain genetic code. store information that determines the activities and structure of the cell
consists of up to 1000 bases, possibilities are enormous

Question 2

chromosomes

Answer 2

dna strands are bound to proteins called histones. each DNA is coiled around the histones so long molecules can fit into a small space
when a cell is about to divide, the coiled chromatin becomes even more tightly coiled to form chromosomes

Question 3

DNA

Answer 3

deoxyribonucleic acid found in nucleus of the cell

contain genetic information that determines the structure of a cell and how it functions

Question 4

steps of DNA replication

Answer 4

1. double stranded DNA molecule unwinds and units by helicase (enzyme), and weak hydrogen bonds are broken
2. primase is required to initiate/start replication. The primer helps DNA polymerase to know where to start copying
3. DNA polymerase: binds to a single strand and helps create/build a complementary strand (using free nucleotides in nucleus) to know where to start copying
4. ligase is needed to glue/seal DNA fragments together
5. the DNA molecule is formed has one strand of the original parent DNA and 1 newly made strand

Question 5

transcription

Answer 5

1. takes place in the nucleus
2. triggered by hormone that enters nucleus and binds to specific gene on DNA
3. RNA polymerase then attaches to begin the process
4. helicase makes the double stranded DNA molecule unzip to allow one of the DNA strands to be decoded (template strand)
   RNA polymerase transcribes the bases on the template strand to make a complementary molecule of mRNA (uracil)
5. mRNA nucleotides floating around in the nucleus find their complement on the DNA strand and bond to gather due to base pair rule
   sequence of bases tell RNaA polymerase to stop copying this release mRNA molecule
6. once the DNA segment has been copied by the mRNA bases, the mRNA strand separates from the DNA. mRNA contains complementary base sequence to original DNA
7. introns are removed (Junk DNA)
8. the mRNA leaves the nucleus via pore and enters the cytoplasm. it attaches to a ribosome for protein synthesis
9. DNA zips up again to create the original double helix

Question 6

translation

Answer 6

1. takes place at a ribosome
2. mRNA is read 3 codons at a time.
   AUG is the start codon, ribosome start making protein, methionine can be removed later
3. tRNA delivers AA to the ribosomes, each tRNA carries a specific AA. the tRNA anticodon, will match with its complementary mRNA codon
4. ribosome works its way down the strand of mRNA reading off the code. (tRNA is recycled, bringing in more AA) rRNA join AA together by forming a peptide bond
5. as process continues, polypeptide chain is formed until a stop codon
6. multiple copies of proteins are made as other ribosomes copy the first ribosome
7. mRNA is recycles, broken up and nucleotides reused
8. after translation, proteins are modified by folding and shortening them in a certain way (enzymes) transported to where the body needs

Question 7

chromatin

Answer 7

in a cell that isn’t dividing, coiled DNA form an untangled network called chromatin

Question 8

dna structure

Answer 8

building blocks are called nucleotides
each DNA consists of two strands of alternating sugars and phosphates with pairs of nitrogenous bases forming cross links between sugar molecules in the two strands
twisted into spiral shape (double helix)
base contains nitrogen atoms, bond between bases are weak hydrogen bonds

Question 9

replication of DNA in interphase

Answer 9

two linked chains in DNA separate because bond between bases is weak
each separated sections half of the original and acts as a template for for nucleotides that form the other half using complementary bases

Question 10

protein synthesis

Answer 10

amino acids joined to form chemical bonds that hold, AA together
joined in ribosome in cytosol of cell. DNA is too big to leave the nucleus so mRNA is used as it is small enough to go through nuclear pores
conversion of genetic code carried by DNA to an end product (protein)

Question 11

genetic code

Answer 11

types of protein a cell makes is determined by it gens.
different genes are activated in different cells (insulin)
triplet codes for amino acids that are joined together at ribosomes

Question 12

nucleosome

Answer 12

8 part histone structure

Question 13

karyotype

Answer 13

photograph of chromosome organised by size shape and banding

Question 14

lipid and carbohydrate synthesis

Answer 14

no genes to carry out instructions

made by enzymes (proteins) indirectly controlled by genes

Question 15

mitochondrial DNA

Answer 15

in mitochondria
small circular molecules
has 37 genes
24 genes code for making tRNA molecules, 13 genes are instructions for making enzymes needed to make ATP
provides information which is needed for mitochondria to function

Question 16

mitochondria

Answer 16

cells and mitochondria are codependent
inherited from mother as mDNA in sperm are destroyed in fertilisation
used for ancestry, evolution and forensics
disease: inability to produce sufficient energy to carry out simple tasks

Question 17

epigenetic

Answer 17

study of changes in gene activity that don’t involve changes in gene code
epigenome: second set of instructions that interact with DNA that activate/suppress expression of certain genes
exposure to certain stimuli can change epigenome

Question 18

acetylation

Answer 18

add acetyl group

cause DNA to unwind enhancing gene expression

Question 19

methylation

Answer 19

adding a methyl group

cause DNA to coil more tightly silences or switches of gene

Question 20

cell cycle

Answer 20

G1 phase: first growth, cells produce new proteins, grows and carries out its normal tasks
S phase: synthesis, DNA duplicates itself
G2 phase: second growth, short phase that involves preparation for cell division
M phase: mitotic, cell divides into two daughter cells

some cells leave cell cycle and stop dividing for years or rest of life. G0

Question 21

interphase

Answer 21

period between nuclear divisions
G1,S,G2
DNA replicates

Question 22

prophase

Answer 22

centrioles become visible early on, move to opposite ends of cell (poles) and microtubules radiate from them form framework of fibres called spindle
nucleolus disappears and nuclear membrane breakdown
chromatin threads of DNA coil to be seines chromosomes (2 chromatid joined at centre with centromere)
chromatids are identical to each other and tightly coiled
coiling makes it easier to distribute DNA to daughter cell
migrate to equator of cell

Question 23

metaphase

Answer 23

chromatid line up at equator

centromere of each pair is attached to a spindle fibre

Question 24

anaphase

Answer 24

each pair of chromatids separate at centromere

new chromosomes are pulled apart towards opposite poles of cell

Question 25

telophase

Answer 25

two sets of chromosomes form tight groups at each pole nuclear membrane forms around each group and nucleolus appears spindle fibres disappear chromosomes gradually uncoil to become chromatin

Question 26

cytokinesis

Answer 26

while telophase occurs, cytoplasm begins to divide | furrow develops between two nuclei and deepens til it is cut in two

Question 27

joined at centromere =

Answer 27

chromatid | not chromosomes

Question 28

cancer

Answer 28

all cancers have common characteristics when a tumour results form uncontrolled division of cells, don't differentiate so the cancer cells can be identified malignant: cells spread throughout the body benign: don't spread to other parts of body but can press on surrounding tissues carcinogen: factors that can trigger cancer (UV, Xray, HPV, ionising radiation, chemicals)

Question 29

cervical cancer

Answer 29

caused by HPV, transmitted through genital skin contact during sex Pap test: cells from cervix detect changes in cells that may develop into cancer

Question 30

breast cancer

Answer 30

mammogram: Xray picture that detects tumours, even really small ones

Question 31

bowel cancer

Answer 31

in large intestine FOBT faecal occult blood test: detects traces of blood caused by polyps/ cancer. polyps can lead to cancer Colonoscopy

Question 32

prostate cancer

Answer 32

no screening DRE, digital rectal examination: feeling prostate for irregularities PSA, prostate specific antigen:checks blood for a specific protein produced by prostate gland rising levels can indicate tumour biopsy: small sample of tissue that can be checked for cancer cells