Biology S1 T3

DNA (2)

a molecule that determines the characteristics of living things

deoxyribonucleic acid

Watson-crick model

Created in 1953 by james watson and francis crick to describe its structure

nucleotides, and what they're made up of (2)

- Basic units of DNA molecule

- phosphate group, deoxyribose sugar and one of four nitrogen rich bases

nucleotide organisation

organisation of nucleotides creates a double helix

uprights of ladder are alternating sugar and phosphate groups

nitrogen rich bases form the rungs

nitrogen rich bases + how they pair (4)

adenine, thymine, guanine and cytosine

- different chemical structures and shapes that complement each other

- can only pair up in one way, a characteristic known as complementary base pairing

(A-T, C-G)

chromosomes (2)

long, thin, thread like structures found in the nuclei of all cells in the human body that contain a nucleus

(some chromosomes found in mitochondria)

- one very long DNA molecule wrapped around in proteins

chromosome number (4)

body cells -> 46 chromosomes, half from mother, half from father

gametes have only half as many chromosomes as body cells

out of the 46, two are sex chromosomes, x and y (XX is female, XY is male

other 44 are autosomes, grouped into 22 pairs, these pairs are made up of homologous chromosomes

homologous chromosomes (3)

same length

structure called the centromere in the same position (the point on a chromosomes that connects two chromatids)

genes for particular characteristics at the same location along their length

genes + difference between one gene and the next (3)

sections of DNA arranged along a chromosomes

difference determined by
- order of bases along the DNA strand
- number of bases in that section of DNA

genetic code (2)

order of the bases along the DNA strand

- each gene codes for a specific protein

proteins (1)

- create the structures and perform actions needed for cells to survive, grow and function


proteins may be
- structural (collagen and keratin)
- enzymes (lactase and amylase)
- regulatory (growth hormone and insulin)

replication

process of copying DNA

why is DNA replication needed? (2)

the two new daughter cells contains the same genetic information, or DNA, as the parent celll. if it does not coccur, the cell cycle will not move forward into the next stage and will die

replication step 1 ( 2)

- strands of double helix seperate from eachother,

- bases are then exposed.within the nuclei there are individual nucleotides that are not yet part of the DNA chain

replication step 2 (2)

1) nucleotides pair up with exposed bases using complementary base pairing

2) sugar and phosphate molecules bond with neighbouring nucleotides

3) and new strands of DNA are formed, identical to parent dna

chromosomes after replication

each replicated chromosomes has the two identical DNA molecules which are now chromatids

chromatids

two identical chromosomes that split and contain the same genetic material

centromere

Area where the chromatids of a chromosome are attached

in the period between divisions

DNA replicates.

asexual reproduction

- offspring are produced without any union of gametes

- produced through mitosis of particular cells

gametes (2)

sex cells
- ova

produced in the ovaries of the female reproductive system

- sperm produced in the testes of th male reproductive system

chromosomes number in gametes? why?

half the diploid chromosomes.

if each parent passed on a complete set of genetic info, offspring would have 4n chromosomes, next gen would have 8n etc.

by halving number of chromosomes in gametes, the number of chromosomes from generation to generation is kept constant at 2n

one chromosome from each homologous pair must en dup in each gamete that is produced, therefore, the gametes have 23 chromosomes in total

female sex chromosomes

XX, homologous pair

male sex chromosomes

XY, not homologous by behave as a pair in meiosis

sexual reproduction (4)

- creates variation in population, so they can adapt to changes in environment

role of male and female reproductive systems to ensure that

- male and female gametes meet

- fertilisation takes place

- the new individual has the best chances

where does meiosis occur in females

ovaries, producing haploid eggs

where does meiosis occur in males

testes, producing haploid sperm

ovaries

releases eggs (ova)

female sex hormones oestrogen and progesterone

cervix (3)

small opening to the uterus

stretches duriing childbirth

allows passageway fo

fallopian tube/oviduct(2)

tubes connecting ovaries to uterus

fertilisation occurs here

uterus/womb (2)

the fertilised egg implants itself in the lining of the uterus to continue growing

baby grows and develops for 9 months of preg

vagina (2)

penis enters here during sexual intercourse

sperm must swim from here to fallopian tubes if fertilisation is to occur

penis (2)

sponge like tissue that fills with blood when male is sexually aroused

tissue expands and is harder than before, causing an erection

urethra (2)

tube running from the length of the penis
empties bladder of urine

allows the passage of semen

testicles/testis (2)

made up of tightly coiled tubes called seminiferous tubules where sperm form and mature

produce male sex hormone testosterone

sperm duct (vas deferens)

connects testes to the penis

bladder

stores urine

epididymis

coiled tubes at the top of the testis in which sperm are stored

prostate gland, cowpers grand and seminal vesicle

add fluids to sperm to make semen (under bladder)

ureters

deliver urine from the kidneys to the bladder

(tube behind bladder

scrotum

sac holding the testes

fertilisation

when a single egg and a sperm fuse in an animal, fertilisation takes place and new offspring are created

fertilisation / chromosome number and division

each gamete carries a haploid number of chromosomes resulting in a diploid off spring. cells then divide by mitosis to develop into a new individual

internal fertilisation

male deposits sperm cells inside the female, usually on land

external fertilisation

the male deposits sperm cells onto the ovum, as the female lays them

usually in water

internal factors (4)

few offspring

sexual reproduction

good parental care and protection

offspring has high chance of survival to adults hood

external factors (4)

many offspring

broadcast spawning

poor parental care and protection

offspring have a low chance of survival into adulthood

advantages of sexual reproduction, what creates variation

creates variation among species, crossing over creates variation

thing to note about this

four gametes produced by gametes are all different

same number of chromosomes therefore same set of genes with information about the same characteristics. however specific information in many of the genes is slightly different

example of difference

in a homologous pair, one chromosome holds infor for blue eyes while the other specifies info for brown eyes. when 4 gametes are formed, half will have the information for blue eyes and half will have info for brown eyes

infertility

the inability to conceive a child after one year (or 6 months if older than 35)

risk factors in females

pcos, uterine fibroids or blocked fallopian tubes

risk factors in males

decreased sperm count and mobility, alcohol use, age, medicines

diagnosing infertility

hysterosalpingography and laproscopy

hysterosalpingography

use of x rays
checks for blcokages
use of special dye
non-surgical

laproscopy

checks for disease/physical problems

no dye used

surigical procedure

uses laproscope

endometriosis

endometrial tissue located outside the uterus

uterine fibroids

a non-cancerous tumour that grows in and around the womb.

polycystic ovarian syndrome

endocrine disorder associated with chronic anovulation

treatments of infertility

zift and ivf

zift

Zygote intra fallopian transfer
an embryo is implanted into fallopian tube

ivf

In vitro fertilisation
embryo is implanted into the uterus

medicines for infertility

human menopausal gonadotroping (hMg) and follicule stimulating hormone (FSH)

hMg

for women who dont ovulate. the hormone is injected and stimulates ovaries to begin ovulation

fsh

hormone which is injected as a treatment and causes ovaries to begin the process of producing ova. often used in conjuction with ivf

mitosis

produces two daughter cells that are identical to the parent cell.

involved in growth and repair of the body.

interphase

period between nuclear divisions. DNA replicates, thus the amount of dna doubles between divisions

Prophase

• centrioles become visible, moving to poles

• nuclear membrane breaks down

• chromosomes become visible

• spindle fibres form
  

metaphase (2)

• chromosomes line up on the spindle fibres at the equator of the cell

• centromere of the chromosomes attach to the spindle fibres

anaphase (2)

• chromatids seperate as spindle fibres contract, now considered as seperate chromosomes. pulled to poles of the cell

telophase (5)

• spindle disappears

• nuclear membrane forms

• chromosomes uncoil, lengthen and become thinner

• cytoplasm divides, as does the remainder of the cell

• cell membrane reforms to produce two daughter cells

cytokinesis (2)

division of nucleus is complete. cytoplasm then divides and the result is two identical daughter cells.

daughter cells grow in size in prep for next round, become specialised cells

meiosis

produces gametes with haploid number of chromosomes

prophase 1

• chromosomes appear and thicken

• centrioles begin to form and move to poles

• spindle fibres form

• crossing over occurs

• nuclear membrane disappears

metaphase 1

chromosomes line up on the spindle fibres at the equator in homologous pairs

anaphase 1

homologous chromosomes move apart to the poles of the cell as spindle fibres contract

centromeres do not divide, chromatids remain in tact

telophase 1

cytoplasm divides,

nuclear membrane reforms to produce two daughter cells.

each cells is now haploid (n)

prophase 2

new spindles form at each end of original spindle at right angles.

chromosomes gradually move towards the equator

metaphase2

chromosomes line up on the spindle fibres at the equator of the cell

the centromere divide so that each chromatid is now a separate chromosome.

anaphase 2

chromatids separate

move to opposite poles of the cell

telophase 2

spindle disappears,

nuclear membranes form,

cytoplasm divides, as does the remainder of the cell.

cell membranes reform to produce four daughter cells with haploid number of chromosomes

embryo vs zygote

An embryo is the early stage of human development in which organs are critical body structures are formed. zygote is a single cell organism formed as a result of fertilisation